Correct engine coolant temperature
 

Hi,

I know this subject has been visited before, but I'll ask it again anyway. What is the correct engine temperature for the Z? Mine seems too hot for my comfort.

If the car is not moving very fast (i.e. bumper to bumper traffic) the guage starts to climb all the way to top, but then just as it touches the cross hatches a fan kicks in and the needle drops pretty quickly to the 3/4 (still too hot for my comfort). I think the radiator is ok because when the fan kicks in (not sure which one) it does start cooling down. Also, when I'm moving at a good clip on the freeway, the needle will go back to the halfway mark or lower.

I would also like to mention I tried looking at the "digital temperature" via the A/C control and it shows 113 when the guage goes all the way to the top (235) - I guess it's in celsius. After it hits that exact temperature the fan kicks in and it drops as stated above.

Any idea whats happening here?

Thanks
Sal

Re: Correct engine coolant temperature
 

Sounds about right.

That is how the stockers are.

Call Marc H. www.ZR1specialist.com for a new chip.

Pete

Re: Correct engine coolant temperature
 

Couple observations..
-The gauges on ZR-1/C4 are notoriously inaccurate
-Coolant temps should be in 190-205 F range
-LT-5 cooling has always been an issue... partly due to the radiator design & placement. Being a bottom feeder (for air flow over the radiator) all sorts of debris (big like leaves) and small (like dirt/grit/sand etc) which can (1) block air flow over the radiator and (2) actually clog the radiator itself (grit build up in the cooling veins of the radiator). Big stuff you can see collected on the front of the radiator, but the small stuff is not readily seen until the radiator shroud is removed.
-OEM program has fans coming on in a progressive fashion and there are aftermarket chips (Haibeck comes to mind :wink:) that reprograms the fans to have both come on and come on at a lower temp than the factory setup.

How many miles on your ZR? Has the radiator core ever been inspected?

Re: Correct engine coolant temperature
 

I have a 94 which means I have a luxury of digital temp readings which 91 does not.

Mine use to run at 198 F at highway speed in cool day and around 202 F on hot weather. What this corresponds to on analog is tough.

As for bumper to bumper, with out AC on, she would reach 223 F at which point fan would kick on and bring down to 218 F or so and turn off until temp would reach 223 or so.

On hot day with AC on, one fan would be running constantly keeping the temp somewhat lower, say about 3-5 degrees.

I wouldn't try to estimate engine temp on analog gage. They are just not that accurate. I see you are in California. How hot a day are we talking about?

Recently I switched to Marc Haibeck chip and and one feature I really appreciate is his cooling fan strategy. Since the switch my Z has been running about 8 to 10 degrees cooler in stop and go traffic.

Re: Correct engine coolant temperature
 

Car has about 32K miles. I had partially pulled off the shroud to look at the radiator. but did not get it all the way out. I did not see any bird nests in there, but obviously I wouldn't be able to see sand in the mesh unless I yanked it completely - I really wanted to avoid that if at all humanly possible.

Re: Correct engine coolant temperature
 

One thing you can try is find a high pressure washer car wash. Then secure the fan so that washer wouldn't run the fan blade and pressure wash between the fan blade blowing out. You can only hit limited area but typically it's the same area where build up was when I pulled the radiator.

http://www.zr1specialist.com/HAT%20W...librations.pdf

Page 12 of this presentation talks about factory fan strategy verses his chip.

Re: Correct engine coolant temperature
 

Hey thanks for your idea - I think I'll give it a try.

Re: Correct engine coolant temperature
 

For reference, today it was 80 degrees here in Northern Virginia. On the highway my Z was running at 201 degrees and it represented 1/6 below half point on analog gauge.
For stop and go traffic, between 203 and 207 (1/8th below half way point on analog). Never saw 210. This is w/ Marc's chip.

Re: Correct engine coolant temperature
 

I am convinced that the cooling problem with the ZR-1 is related to the bypass flow around the radiator. In both my 1990 ZR-1 and my 1993 ZR-1, I have brand new high capacity radiators (a DeWitt and a Ron Davis) and Haibeck chips.

In both cars when cruising at about 55 mph in sixth gear (about 1600 to 1800 rpm, the coolant temperature will rise to around 225. If I shift to fifth gear, (>2000 rpm) the temperature immediately drops to around 203-205. The drop is rapid (you can see the needle move). This indicates to me that there is plenty of cooling capicity available (ie air flow and heat transfer from the radiator) but that at low rpm most of the water pump output flow is bypassing the radiator through the radiator bypass line.

Under higher engine load, such as running at 80-85 mph the coolant temperature is stable at around 195.

My next research attempt is going to be replacing the thermostat (which also has the bypass flow valve built into it. I may even try to block off all the low rpm bypass flow just to see what happens.

Jim

Re: Correct engine coolant temperature
 

Change to 4.10 gear

Re: Correct engine coolant temperature
 

I know what your saying because I do notice a change in engine speed does affect the temperature almost immediately. But with that said, I'd be very careful about defeating the bypass feature as this may send too much water presure through the radiator and possibly blow it out.

Re: Correct engine coolant temperature
 

You can use a long bent piece of wire from a cloths hanger to get stuff out.
To avoid getting stuff in there see:
http://www.zr1netregistry.com/ZR1_radiatorscreen.htm
Mine is a stock LT5 in a 90. I run 220 in traffic.
As mentioned by others, keeping the AC on and using 5th gear keeps temp
lower.

Re: Correct engine coolant temperature
 

Guys - I think I found the reason but I'm not sure.

Do any of you know the the sequence of the two fans? When the temperature gets up to about 235 I notice the PASENGER side fan comes on religiously. But I also noticed that the DRIVER side doesn't seem to be spinning at all - does it come on at an even higher temperature or should it have been running BEFORE the passenger side fan?

Thanks,
Sal

Re: Correct engine coolant temperature
 

Comes on when AC is turned on.
You can use this to keep it on and lower the coolant temp.

Re: Correct engine coolant temperature
 

it will ONLY come on whith the A/C?

Re: Correct engine coolant temperature
 

My driver side does not come on with or without A/C turned on.

Re: Correct engine coolant temperature
 

It should come on with a/c, maybe a bad relay? connection?

Re: Correct engine coolant temperature
 

If the High presure side of the AC line never reaches 240psi then the
fan does not get told to turn on. Check to see if the AC is working.
Does it get cold? If so maybe the fan or (of fan relay) is bad?
Check connection at the fan.

Re: Correct engine coolant temperature
 

That is unusual! I never noticed anything similar on 91 nor 94.
Maybe, I just didn't notice? I will duplicate your description later today.

Re: Correct engine coolant temperature
 

I agree, I think. It appears to me that my 90 will become more heated if I spend much time in the lower gears, like doing road work where 3rd & 2nd & 4th are used alot....specially if I slow down and cease playing and drive normally. At that point it appears that I heat soak for a good while till the cooling system calms down or catches up to the heat load that I just generated by my sophomoric behavior...:redface:...it appears that the higher I go in the rev band, and the longer I stay higher in the revs, the more by-passing takes place in my 90's cooling system? It appears if I insist in living up past the 4k mark that after a good while the oil & coolant temps start to spike even if my velocity is at a good clip. I seem to get my best cooling performance when I can keep to about 2k or below in 5th or 6th with a constant speed. Maybe I have something malfunctioning?:confused:

Re: Correct engine coolant temperature
 

my A/C definitely comes on cold. I did notice the drivers side fan was hard to turn with my hand, then it felt like it broke loose and I could turn it again. I see two relay looking things together on the left side of the fan shroud - are these the two relays?

Re: Correct engine coolant temperature
 

You are correct about 4.10 rear end. The '93 has a 4.10. Same effects that I noted. It just happens at different speed/gear combination.

As far as using a pressure cleaner hose to blow crap out of the radiator, be very careful. The fins in these radiators are very thin aluminum and it would be easy to bend them over with a pressure washer.

Thanks for the warning about reducing the bypass flow and causing over pressure in the radiator. I plan to proceed carefully. The over pressure problem will only occur at high water pump flow (engine rpm at 7000). At that water pump pressure, the coolant bypass will be opened against its spring pressure.

http://i407.photobucket.com/albums/p...twithwords.jpg


What I am trying to reduce is the bypass flow that occurs all the time (even at low pump pressure) because of the notches in the bypass valve disc.

I would like to find a ZR-1 that doesn't do what I described and find out what brand thermostat it has.

Jim

Re: Correct engine coolant temperature
 

Tom,

I think you are seeing two effects.

1. If after a period of spirited driving (increased engine heat load), the temperature is high, you may have a radiator fouling problem. But if the temps are not way high, then the fouling problem is not too severe.

2. The worst cooling capability for my LT5 occurs at light load (5-10% throttle) and low rpm (< 2000 rpm). Because of the notches in the bypass flow valve there is barely sufficient water flowing through the radiator to remove the heat load. At these conditions, even with a perfectly clean radiator and perfect air flow (both fans running) the temperature of the coolant will rise way above the desired temperature.

Jim

Re: Correct engine coolant temperature
 

Sal, yes the two relays that you find on the left side of the radiator shroud are the fan relays. It sounds like one of the motors has a bearing issue if it wouldn't turn freely. I'd keep an eye on that one.:thumbsup:


Jim, thanks for your advice. I will have to admit that when I was trying to clean my OE radiator that after a while I gave up on the sand particles....I didn't get them all for sure!:o

Oh well, I guess it's time to start shopping for a new radiator as I'm very OCD about the coolant dump & flush & t-stat R&R every two yrs. Perhaps a Marc Haibeck EPROM is in order also.

Re: Correct engine coolant temperature
 

Tom,

I definitely recommend the Haibeck chip for the fan control feature as well as all the other improvements it offers.

I wonder if there is a way to use a local radiator shop to dip clean the stock Corvette radiator. I don't know if that can be done to the plastic tank radiators though.

Jim

Re: Correct engine coolant temperature
 

Jim,

I replicated and confirmed that my Z with OEM thermostat does the same thing.
Sustained 55-60 mph in 6th - 213
Down shift to 5th, temp drops to 202
Sustained 65 in 6th - 208

Ambient temp was around 84.

Generally I prefer not lug the motor so I don't get into 6th unless I am running sustained 70 plus. That's probably I was never aware of this.

Re: Correct engine coolant temperature
 

SC

Thanks for taking the time to check this out.

I am trying to figure out if the notches in the bypass valve have some other purpose in the overall cooling system operation.

Possible reasons for the notches might be: faster engine warm up when starting in cold weather; better responsiveness by the thermostat; improved heater operation with cold engine; temperature stabilization of the entire cooling system; or I don't know what else.

Ideas anyone?

Jim

Re: Correct engine coolant temperature
 

Jim, I don't believe this is coolant bypassing the radiator. That should only happen when the pressure gets high.

I posted about this on the listserv a while back. I believe it is related to the flow capacity of the pump at low rpms. Graham Behan sent me a chart of the flow rating at various rpms, and mentioned it was likely that at those lower rpms, the pump does not flow enough. This is why downshifting helps.

Re: Correct engine coolant temperature
 

Bob, Looking at the picture I posted, the bypass valve has two openings (notches) that allow flow to bypass the radiator even when the bypass valve is closed (low pump pressure). In the picture only one notch is shown. The other is just as large and together I think that they cause a relatively large amount of water to bypass the radiator even at low water pump pressure/flow.

Jim

Re: Correct engine coolant temperature
 

I hear what you are saying Jim. I was thinking further about this. I suspect if the pump pumped so little that it all bypassed the radiator, then the car would not cool down when idling. Yet that's not true, at the lowest flow point, the car can still shed heat when the fans turn on at idle.

FYI, while hardly definitive, I had a quick write-up in HotB issue 15 if you want to give it a quick read. :)

Re: Correct engine coolant temperature
 

You will blow your head gaskets! The thermo temp spring opening depends on the hot water coming down the bypass to see opening temerature. No hot water, no open, blow head gasket.

You can cut the thermo pill spring and block the bypass, this will result in the coolest operating temps.

http://www.deliquescence.net/~tyler/misc1/Thermo.jpg

Tyler

Re: Correct engine coolant temperature
 

At what temp would damage to the engine occur? That seems to be more important than who's car runs the coolest and why?

Re: Correct engine coolant temperature
 

You get over 260 for any length of time and depending on the age/miles of the engine bad things begin to happen. The location of the water temp pickup can result in a misleading temp on the guage if there is low water in the motor. It is one of the first locations to see steam vic water which results lower temp reading. You need to watch oil temperature reading too.

Tyler

Re: Correct engine coolant temperature
 

Jim thanks for the recco on Mr Haibeck's chip....I've been willing to live with it till now. It's just no fun any longer having to stop playing when the temps start to rise and wait for the stock programming on the fans to do it's cooling job. I get really paranoid when the oil temp gauge gets to 1/2 way and the water temp gauge stays at 3/4 or more! It just scares the chit outta me. I swear I can't get my head around when my C5 & C6 buddies push it till the DIC tells them "reduced power mode/ temp warning"....I'd have had two heart attacks by that time!:redface:

I guess I'll ask Mr. Haibeck if I could buy a prom with the fan programming changed to what he says it should be.

Re: Correct engine coolant temperature
 

QB,
96-2000 Ford Mustang 4.6L uses the same style t-stat with bypass valve but it doesnt have the cutouts. I used one for a while and didnt notice any difference. If you get rid of the bypass you wont have coolant flowing through the block when the t-stat is closed.

Re: Correct engine coolant temperature
 

Thanks 8upZR1. I will get one of those without the notches and drill a hole to keep the temperatures equalized. Then I should be able to reduce the bypass flow at low enginr rpm.

Bob, Regarding the question of maintaining low engine temperature at idle, my 1993 will do that. I never could leave the car idling before I replaced the radiator. Now I can. Coolant temp stays at 198. I guess the engine heat load at idle is enough lower than the engine heat load at 1600 rpm and 50 mph that the limited radiator flow can keep the coolant temp down at idle.

Tyler, Thanks for the input. Do you think that a small hole drilled in the body of the thermostat would allow enough flow to ensure that the thermostat does respond to coolant temp?

Jim

Re: Correct engine coolant temperature
 

you might try drilling 2 1/16 in holes along the edge of the thermastat just inside the rubber seal. it takes the car longer to heat up. i did this with the 92 and the car with a 180 stat runs 182-184. i tried 3 holes but the car wanted to run below 180 which i didnt want on an alluminum engine

Re: Correct engine coolant temperature
 

I have a 165 thermostate (zr-1 speciality products) if anyone needs it $100

reprogram the fans, or you can install a switch to control it manually.

I have the big ron davis rad, and the only time I run hot is with the ac on creeping along for 30 min in traffic in 90 deg weather

revving the car up helps, or turning off the ac

pete did an interesting thing and went to an electric pump

not as much flow and not a mod for racing but it increases flow at idle and seems to keep the car cool under normal driving

with the big radiators they "recover" much quicker once you get moving, but they don't work well at low speeds because the fans have a hard time pulling the air throught the much thicker cooling stack

anyone know of bigger better fan setup??

Re: Correct engine coolant temperature
 

Interesting. Thanks

Re: Correct engine coolant temperature
 

There was probably a rock between the fan and the housing which will stall the fan motor and blow the fusible link at the connector at the rear of the battery.
Replace the link with the correct gauge wire or an in-line fuse - a 30 amp fuse will do the job. And yes, those are the two fan relays.