Thermostats and Thermostat Housings

[Dynomite]

Here is How My Day Went

After a New Fluidyne Radiator Install I thought I should go all the way and put in a New 180 deg Thermostat. Marc answered a question I had in that regard. The thermostat for all LT5's is the same. The temperature rating is 180 degs F. In detail, the thermostat begins to open at 175 and is fully open at 185 degrees. A thermostat with over 50k miles generally opens 5 degrees later and opens about 80%.

So.....why not. I checked my New 180 deg Thermostat in Hot Water and it started to open at approximately 175 deg. Ready to go...and I had my Post on LT5 Thermostats on hand :p

Post 7 - LT5 Thermostats (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp.html#post1580070558)
Post 237 - Blocking TB Coolant, Fluidyne Radiator and Thermostats (http://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759179)

Well......the New Fluidyne Radiator Drain Port worked perfectly. Now to separate the Thermostat Housing Halves. OOPS!!!!!

It all went down hill from there on.....:D

1. Bottom Bolt on Thermostat Housing was frozen Solid. Broke it off.
2. Had to remove Belt Tensioner, to get my hands in to move AC Dryer and to get to Lift Thermostat Housing.
3. Also removing Belt Tensioner gives access to the Spring Clamps on both ends of the Radiator Hose connected to Water Pump.
4. The Hose from Water Pump to Thermostat Housing is the only Coolant Hose I have yet to replace.
5. Disconnected Passenger Side hose to Heater Nipples on Thermostat and got it free (what a corroded mess).
6. Cut the Coolant Hose going over rail to Thermostat Housing.
7. Finally got Thermostat Housing up and out after moving the Top Coolant Hoses connecting Each Injector Housing.
8. Once the Thermostat was lifted up so I could get to the Drivers Side Heater Nipple....Disconnected that Heater Hose.
9. The Water Pump Spring Clamp was completely turned impossible to get a pliers on it so I used an Air Grinder.
10. Oh...ya.....Got the Hose Clamp cut but all I did was cut a piece out that allows you to compress the ends together. Now what a mess :o
11. After a couple hours with a razer blade and screw drivers finally got that hose off the water pump.
12. OOPS.....forgot about the frozen Bolt in Thermostat Housing which I had to use Acetylene Heat.
13. After heating finally got the stud showing to move back and forth and 30 minutes later got the stud out of the Thermostat Housing.
14. Chased the Threads in the Thermostat Housing.
15. The Drivers Side Heater Nipple on the Thermostat Housing has an "O" ring and the inside where the "O" ring resides was corroded.
16. Thanks to Jerry having much more foresight than myself I ordered a New and Improved Thermostat Housing Heater Nipple.

THIS ALL STARTED THIS MORNING AT 9:00AM AND ENDED AT 5:00PM THIS AFTERNOON !!!!!!!!!

This should be titled "You think you got Problems" :sign10:

Oh......Checked that Stock Thermostat (must have been stock since the bolts in the Thermostat Housing were frozen solid) for Function.

I suspect it be a 180 deg Thermostat. It started to open at 195 deg and never opened all the way as far as I could tell.

So....what started off a great day with great idea had some tuff spots but ended up solving several issues including Corroded Thermostat Housing, Old Water Pump Hose that needed replacement, Corroded Heater Nipple on Thermostat Housng, and finally found out that what Marc had suggested about Thermostats was exactly what I found with the poor condition of my Stock 180 deg thermostat.

Installed the NEW Jerry's Thermostat Heater Nipple on the Thermostat Housing. After Cleaning up both Heater Nipples and with the New Heater Nipple installed I popped on the Heater Hoses. I acutally used just a tad of Permatex on the nipples for ease of insertion and a bit of additional leak protection. I also installed one new Water Pump to Thermostat Housing Coolant Hose. Fired up the LT5 after filling with Coolant and took it for a spin. No Leaks and Coolant Temperature stayed about 15 deg cooler than with the worn out Thermostat that actually opened at 195 deg (the New 180 deg Thermostat opened at 175 deg).

Just a Heads Up......if you ever have to remove the Thermostat Housing for any reason, have on hand one of Jerry's New Heater Nipples to replaced the old Heater Nipple on the Thermostat Housing. Jerry's New Heater Nipple (http://www.jerrysgaskets.com/nipple-heater-coolant-return-90-95-7c4/)

As an aside See Item #9 Post 237 - Blocking TB Coolant, Fluidyne Radiator and Thermostats (http://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759179)..........My thinking is that the whole purpose of the Dual Opening Thermostat Housing (Thermostat can open at the Temperature side or on the other end at the Pressure side) is to keep Radiator Pressure to acceptable limits. In other words the Thermostat functions when the engine is cool and when the engine is at high rpm.

When the engine is at high RPM, the Bypass on the thermostat will be open completely do to the water pump developed coolant pressure on the bottom of the Thermostat. This Higher pressure being developed at the bypass end of the thermostat because the Thermostat is closed on the Temperature end or because the high water pump RPM is developing too much pressure on the radiator on the Bypass end of the thermostat.

In other words the Thermostat can open on either end (one end temperature controlled and the other end differential pressure controlled). And even if the Temperature End of the Thermostat is fully open, HIGH water pump RPMs may develop greater pressure than the radiator can stand on the Bypass End and the Thermostat would then open on both ends to allow more coolant to recirculate rather than ALL of the coolant flow being forced through the Radiator . 7,000 Engine RPM does that to you :p

[efnfast]

Lernt me some stuff about thermostats. Thanks Dynomite.

[XfireZ51]

Thermo housing is definitely a candidate for 3D printing.

[Tripler]

Awesome update and tips Dynomite . Sounded like a hell of a job .

;)

[5ABI VT]

Looks like ill be getting that nipple ! Planned to pull apart the shroud and rad for cleaning and tinkering with the thermostat soon. Btw does anyone make a 170 or something slightly cooler than the 180 factory thermostat?

[Dynomite]

Looks like ill be getting that nipple ! Planned to pull apart the shroud and rad for cleaning and tinkering with the thermostat soon. Btw does anyone make a 170 or something slightly cooler than the 180 factory thermostat?

I think you can find cooler Thermostats down to 160 deg but my theory is the LT5 engine operates best with 180 deg Thermostat and both a 160 deg and 180 deg thermostat will be fully open at say 185 deg F.

The 160 deg just opens sooner but does not keep the engine cooler than a 180 deg thermostat once the 180 deg Thermostat is fully open. The 160 deg thermostat will keep the engine down to say 165 deg on cool days which is too cold I think. The cooler Thermostat will set the bottom temperature but does nothing to set the top temperature once both thermostats are fully open.

[Paul Workman]

I think you can find cooler Thermostats down to 160 deg but my theory is the LT5 engine operates best with 180 deg Thermostat and both a 160 deg and 180 deg thermostat will be fully open at say 185 deg F.

The 160 deg just opens sooner but does not keep the engine cooler than a 180 deg thermostat once the 180 deg Thermostat is fully open. The 160 deg thermostat will keep the engine down to say 165 deg on cool days which is too cold I think. The cooler Thermostat will set the bottom temperature but does nothing to set the top temperature once both thermostats are fully open.

I never took 'thermal dynamics', so I don't know the proper physics terms for it. But, you're right: The greater the heat differential between the radiator (coolant) and the ambient air, the greater the rate at which (therms or calories or whatever) will transfer (to the air, in this case)*.

*Plotting the temp over time, the graph would describe the change over time according to the natural log of decay (http://www.mathsisfun.com/algebra/exponential-growth.html). This would explain why it usually requires a lager capacity radiator and sometimes increased (fan) air volume coupled with a lower temp thermostat to bring the coolant temperature down to the lower 'stat opening point. IOW, the closer the coolant is to the ambient air temperature, the slower the coolant temperature falls (unless and until the motor adds more heated coolant to the radiator), all else being equal.:)

[Dynomite]

I never took 'thermal dynamics', so I don't know the proper physics terms for it. But, you're right: The greater the heat differential between the radiator (coolant) and the ambient air, the greater the rate at which (therms or calories or whatever) will transfer (to the air, in this case)*.
*Plotting the temp over time, the graph would describe the change over time according to the natural log (http://www.mathsisfun.com/algebra/exponential-growth.html) of decay (http://www.mathsisfun.com/algebra/exponential-growth.html). This would explain why it usually requires a lager capacity radiator and sometimes increased (fan) air volume coupled with a lower temp thermostat to bring the coolant temperature down to the lower 'stat opening point. IOW, the closer the coolant is to the ambient air temperature, the slower the coolant temperature falls (unless and until the motor adds more heated coolant to the radiator), all else being equal.:)

I took Thermal and other stuff but much easier to explain with just plain logic. When both the cooler and hotter Thermostats are fully open (assuming both allow the same flow) there is NO advantage using the cooler Thermostat. When it is HOT outside and you are operating above the full open Coolant Temperature of the Hotter Thermostat.

There is a DIFFERENCE however when operating on COOLER Days when the Coolant Temperature does NOT rise to the FUll OPEN Conditiaon of the Hotter Thermostat. Then you are operating with a PART OPEN 180 deg Thermostat and maybe a FULL OPEN 160 deg Thermostat. Or when really cool outside. A PARTLY Open 160 deg Thermostat and a CLOSED 180 deg Thermostat. In OTHER WORDS your Coolant Temperature is Held Below 180 Deg which is NOT GOOD for the LT5.

The LT5 is designed for 180 deg I think as that is the Thermostat it comes with albeit my 95 had a 190 deg Thermostat which I changed out for a 180 deg (I think the 180 deg original Thermostat just drifted to a higher opening temperature with age as Marc suggested).

[Hog]

I never took 'thermal dynamics', so I don't know the proper physics terms for it. But, you're right: The greater the heat differential between the radiator (coolant) and the ambient air, the greater the rate at which (therms or calories or whatever) will transfer (to the air, in this case)*.
*Plotting the temp over time, the graph would describe the change over time according to the natural log (http://www.mathsisfun.com/algebra/exponential-growth.html) of decay (http://www.mathsisfun.com/algebra/exponential-growth.html). This would explain why it usually requires a lager capacity radiator and sometimes increased (fan) air volume coupled with a lower temp thermostat to bring the coolant temperature down to the lower 'stat opening point. IOW, the closer the coolant is to the ambient air temperature, the slower the coolant temperature falls (unless and until the motor adds more heated coolant to the radiator), all else being equal.:)
Yes Paul, your explanation is correct. IOW The rate of heat transfer is directly proportional to the heat differential

A house with an internal temperature of 80ºF and outside temp of 40ºF will lose heat at a faster rate than a house with an inside temp of 70º and outside temp. of 40º.(of course when all else is equal)

[Hog]

I think you can find cooler Thermostats down to 160 deg but my theory is the LT5 engine operates best with 180 deg Thermostat and both a 160 deg and 180 deg thermostat will be fully open at say 185 deg F.

The 160 deg just opens sooner but does not keep the engine cooler than a 180 deg thermostat once the 180 deg Thermostat is fully open. The 160 deg thermostat will keep the engine down to say 165 deg on cool days which is too cold I think. The cooler Thermostat will set the bottom temperature but does nothing to set the top temperature once both thermostats are fully open.
Emphasis mine.

I think the bolded statement pretty much sums up thermostats with various opening points.
The purpose of a thermostat is to allow the engine coolant to circulate through the engine without it being cooled, this allows the engine coolant temperature to rise. Without that thermostat, the cold engine coolant while being heated by the warming engine block, will be simultaneously cooled by the radiator. We want the engines heat to warm its engine coolant as quickly as possible to be able to warm the cabin as quickly as possible and also to get the engine up to operating temperature for both decreased wear and fueling concerns.
Once the engine coolant has been heated enough, the thermostat opens allowing engine coolant to flow through the radiator circuit for cooling. Once that rad circuit is opened the only way control the engine coolant temperature is to either:
1) Change the amount of heat being introduced into the engine coolant (turn off engine, slow engine revs)
or conversely
(increase engine revs, increase engine power output etc)

2) Change the amount of heat being taken from the engine coolant: increase airflow across the rad via fans/roadspeed, engage the cabin heater/fan
or conversely
disengage the rad fans, physically block airflow across the radiator etc.

Of course this is over simplified, there are other things at play such as bypasses, thermal shock and many other things at play, but the basic purpose of the thermostat is simple. Delay the cooling function of the radiator until enough heat has been produced by the engine.

[Dynomite]

Delay the cooling function of the radiator until enough heat has been produced by the engine.

As you suggest the purpose of the Thermostat is to stabilize the engine heat at a target of 180 F deg in all environments. But as experienced when temperatures ambient exceed 90 deg F there are Engine Cooling issues associated with the LT5 especially in Stop and Go Traffic using the Stock (but clean) Radiator.

The cooler Thermostat will set the bottom temperature but does nothing to set the top temperature once both thermostats are fully open.

This is assuming both a 160 deg F Thermostat and 180 deg F Thermostat both allow the same maximum coolant flow which seems to be the case as I observed maximum opening area on both.

A cooler 160 deg F Thermostat does nothing to cool the engine better in the situation described above on a HOT day when both 160 deg F and 180 deg F Thermostats are FULLY OPEN. But.........if one wants to experiment.

If you drill additional holes in the 180 deg F Thermostat around the periphery as Jerry suggested at one time.....you might be able to actually drop the max coolant temperatures in the HOT situation described above while not dropping to the cooling effects associated with a 160 deg F Thermostat on cool days. In other words reach a happy medium. But realize that those additional Thermostat Holes are open from the start so the engine temperature rise will be slower getting to operating temperatures of 180 deg F.

[Hog]

Since a thermostat can either be, closed, open or somewhere in between, once the thermostat is fully open, at that point, it is ordering for as much coolant flow through the rad as possible. It is now up to the rad to do its job. If engine coolant temps continue to rise to the point of overheating, not enough heat is being removed from the system compared to the amount of heat being added.

It would be very interesting to see the GM data from the LT5 car desert testing. Heck if Chev is dishing out info, I'd take a copy of all the Stillwater dyno printouts as well.

[efnfast]

I would think that the thermostat being fully open is rare. If it were common, the temp would exceed 180 frequently. I don't think that is the case. We also need to take into account water flow via pump speed, which is governed by engine speed.

[Dynomite]

I would think that the thermostat being fully open is rare. If it were common, the temp would exceed 180 frequently. I don't think that is the case. We also need to take into account water flow via pump speed, which is governed by engine speed.

I would say not rare at all but actually almost always fully open at temperatures above ambient 90 deg F

[efnfast]

I would say not rare at all but actually almost always fully open at temperatures above ambient 90 deg F
I repectfully disagree. A fully open thermostat represents the max cooling the system can handle. Disregarding air flow and water flow which are kinda' manually controlled.

[Dynomite]

I repectfully disagree. A fully open thermostat represents the max cooling the system can handle. Disregarding air flow and water flow which are kinda' manually controlled.

I have tested many Thermostats and all the 180 deg F Thermostats start to open around 175 - 180 deg F and are fully open around 190 deg F.

On my digital readout on a 90 deg F day my coolant temperature is running 190 - - 200 deg F. On hotter days my Coolant Temperature is running over 200 deg F and up to 210 deg and a bit higher.

Which of my observations are you disagreeing with :p

Actually if you disagree with my observations.....End of Discussion ;)

Oh.....Five ZR-1s all running Aluminum After Market Radiators and ALL with 180 deg F New Thermostats installed.

[George Maz]

Oh.....Five ZR-1s all running Aluminum After Market Radiators and ALL with 180 deg F New Thermostats installed.
Can you list your favorite choices for Aftermarket Aluminum Radiators? ...obviously FLUIDYNE is at the top, but it's no longer made.
Criteria of fitment, cooling, cost, and particulars, etc.

The repair & modification guides you post on the forum are outstanding. Thank you for taking the time to do so.

[Dynomite]

Can you list your favorite choices for Aftermarket Aluminum Radiators? ...obviously FLUIDYNE is at the top, but it's no longer made.
Criteria of fitment, cooling, cost, and particulars, etc.

The repair & modification guides you post on the forum are outstanding. Thank you for taking the time to do so.

Interesting question....I just had to buy Hib's Fluidyne for my 95' couple weeks ago as it was stored in the original box for probably years....it was mint and is a great radiator. I cannot tell for sure how well the Fluidyne does in heat as I also replaced a Thermostat that was opening at 195 deg F rather than 180 deg F.

Marc suggests that old Thermostats creep up in opening Temperatures as well as creep down in Opening Area.

http://i287.photobucket.com/albums/ll142/dynomite007/Dynomite16/83470738-3787-470a-9bd6-988d258581e6.jpg

Blocking TB Coolant and Fluidyne Radiator (http://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759179)

The Fluidyne has a thicker core than stock and comes within 1/8 - 1/16 inch of the internal fan baffles but does not require any baffle trimming.

I use Ron Davis in two ZR-1s which has a thicker core and requires removing 3/8 inch of the internal fan baffles on the 90' and 91'.

One 90' ZR-1 came with a Dewitt and another 90' came with a nice aluminum of unknown brand. Both function super but am not sure in HOT climates as have not run those in ambient temperatures over 90 deg F. I actually switched those two Radiators between ZR-1s as I wanted the Dewitt in the 90' with Headers :D

Also.....having removed several stock radiators I have found the crimped plastic type end caps usually are found leaking or have leaked.

I always make sure the radiator is super clean and I install a Debree screen on all. I also clean the AC coils and the Oil Cooler coils. Lastly I always install a NEW 180 Deg Thermostat.

Costs for the Ron Davis, Fluidyne and other good quality aluminum radiators are in the neighborhood of $500-$600.
You want the Aluminum Radiator WITHOUT automatic transmission cooling and all of the Aluminum Radiators I have installed went in easily with the only issue being trimming of the internal fan baffles for the Ron Davis.

Oh....the trick on removing the Radiator Housing/Cover.

1. Remove all bolts holding the Radiator Housing.
2. Remove the Oil Cooler Flange Adapter (and two oil cooler hoses) from the Oil Cooler.
3. Remove the Air Cleaner housing and Corrugated Connector.
4. Disconnect ALL Fan Shroud screws top and bottom including the two screws holding the AC Dryer.

5. Now....the trick.....Lift up the Housing on the Drivers side clearing the hood hinge which will take some pressure but nothing will crack or break. Lift that Housing on the Drivers side as high as you can.
6. Now....the trickiest......Lift up the Housing on the Passenger side bending the Housing Tab inside the AC lines (you can bend them a lot with no damage).

7. The Housing will then be free.

Now the BIG TRICK....Disconnect the Thermostat Housing two bolts to the frame and the single bolt holding the Thermostat Housing pipe pointing to the Drivers side. The Thermostat Housing can then be moved so you can disconnect that lower radiator hose. You can then split the Thermostat housing (I had a frozen bolt on the last one which is another story).

Use a flat scraper blade to hold the New Thermostat in place tight (as it wants to spring outward as the main spring is compressed when installed) as you install the two Thermostat Housing halves (yes....I use a bit of Permatex on the faces of the Thermostat Housing and on the rubber seal of the Thermostat) :D

You do NOT want to pinch that Thermostat rubber seal on the flat surfaces of the two Thermostat Halves (the rubber seal resides in a groove of the Thermostat Housing Half containing the Thermostat).

See Item #6 Blocking TB Coolant, Fluidyne Radiator, and Thermostats (http://www.corvetteforum.com/forums/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-12.html#post1590759179)

[Hog]

Any closeup pics pf the fin design of some of these aftermarket radiators? Its amazing how the more modern OEM designs are able to have fewer cores/less thickness and are still able to cool better than older designs.
In an effort to reduce the amount of materials, therefore make a radiator that does the job for the least amount of money, there have been some impressive advances in radiator design.


I used to think that a radiator fin was a radiator fin, not so much anymore.
Here is one pic that shows some of the design going on.
http://www.oncyprus.com/media/ems/biz/sites/16928/files/Machinery/Airway-Fin-machine1.jpg
http://i01.i.aliimg.com/img/pb/816/182/701/701182816_397.jpg




I remember as a kid on road trips with my Dad, I would read the owners manuals of whatever vehicle we were driving and it was suggested that if in a situation of overheating, to shift into Park/Neutral and hold engine rpm at 1500-1800rpm until temperature came down. Of course this is relying on increased coolant and airflow circulation through the radiator to bring coolant temps down.

Obviously doing so with an LT5 would only increase coolant flow as the fans are already working at full duty cycle.

[George Maz]

....I just had to buy Hib's Fluidyne for my 95' couple weeks ago as it was stored in the original box for probably years....it was mint and is a great radiator. Costs for the Ron Davis, Fluidyne and other good quality aluminum radiators are in the neighborhood of $500-$600.
You want the Aluminum Radiator WITHOUT automatic transmission cooling and all of the Aluminum Radiators I have installed went in easily with the only issue being trimming of the internal fan baffles for the Ron Davis.
Last year I purchased a C4 FLUIDYNE new in the box, but it's the automatic transmission version. Are there any special considerations to installing it? Plug the unused ports and it's the same as the manual transmission version?...or I'd have a separate cooler/warmer section if needed for something else.

[efnfast]

I have tested many Thermostats and all the 180 deg F Thermostats start to open around 175 - 180 deg F and are fully open around 190 deg F.

On my digital readout on a 90 deg F day my coolant temperature is running 190 - - 200 deg F. On hotter days my Coolant Temperature is running over 200 deg F and up to 210 deg and a bit higher.

Which of my observations are you disagreeing with :p

Actually if you disagree with my observations.....End of Discussion ;)

Oh.....Five ZR-1s all running Aluminum After Market Radiators and ALL with 180 deg F New Thermostats installed.
Based on that info, I would agree. If the temp is above 180, I would expect the thermostat to be fully open. I don't think my temps ever exceed (under normal driving conditions) the expected temps. However, I've never watched with a digital.

[Chedberg]

Based on that info, I would agree. If the temp is above 180, I would expect the thermostat to be fully open. I don't think my temps ever exceed (under normal driving conditions) the expected temps. However, I've never watched with a digital.

On the AC/Heater head unit, hold the Up and Down Fan Buttons until a -00- appears. Then use the Up or Down button to change the number to -16. Hit the center Fan button. The AC/Heater display will now show the engine coolant temperature in Celsius. In my experience, with an aluminum radiator and 180 degree thermostat, it should stabilize somewhere around 90-95 degrees C.

[XfireZ51]

On the AC/Heater head unit, hold the Up and Down Fan Buttons until a -00- appears. Then use the Up or Down button to change the number to -16. Hit the center Fan button. The AC/Heater display will now show the engine coolant temperature in Celsius. In my experience, with an aluminum radiator and 180 degree thermostat, it should stabilize somewhere around 90-95 degrees C.

Or buy a 92ZR and check coolant temps as most other humans do. ;)

[Dynomite]

On the AC/Heater head unit, hold the Up and Down Fan Buttons until a -00- appears. Then use the Up or Down button to change the number to -16. Hit the center Fan button. The AC/Heater display will now show the engine coolant temperature in Celsius. In my experience, with an aluminum radiator and 180 degree thermostat, it should stabilize somewhere around 90-95 degrees C.

Yes....you describe perfectly how to get digital Readout of Coolant Temperature in deg C on the AC Head Unit on the 90'-91' and I assume 92'.

On the 95' you can press GAUGES on Dash and get Digital Readout of Oil Temperature and Coolant Temperature in deg F on the SPEEDO Cluster (I think where TRIP Information is shown as I recall). Pretty Cool I would say :p

And YES.....the Coolant Temperature on my 95' stabilizes right around 90-95 deg C on a 90+ deg day with a Fluidyne Radiator installed :thumbsup: