Leaky Radiator

[Gary Yarbrough]

On Friday, I spent some time trying (yet again) to troubleshoot my rough idle. I should have known better, given that it was the 13th! No luck... I was shut down early because of another issue.

I found that I have a leak in my radiator. This is the 2nd radiator to go bad in the last six months. I remember reading once that the cooling system has a pressure relief function. Can someone enlighten me on how that works and if some flaw in that system is causing my radiators to go bad? Is there something else that is likely to be causing my problems?

[secondchance]

On Friday, I spent some time trying (yet again) to troubleshoot my rough idle. I should have known better, given that it was the 13th! No luck... I was shut down early because of another issue.

I found that I have a leak in my radiator. This is the 2nd radiator to go bad in the last six months. I remember reading once that the cooling system has a pressure relief function. Can someone enlighten me on how that works and if some flaw in that system is causing my radiators to go bad? Is there something else that is likely to be causing my problems?

Are you running low temp thermostat?
Before I found out our thermostat needs bypass holes I had a 160 degree thermostat installed without any bypass. I strongly suspect this led to my radiator failure.

[Gary Yarbrough]

I believe I'm running a stock thermostat. But, it could have been changed before I bought the car and not recorded...

[secondchance]

Also check and, if necessary, replace coolant reservoir cap. This is another point of pressure relief.
As far as I know, these two, improper thermostat and/or reservoir cap, are only things that could hold pressure to a point of rad failure.
Pressure relief function you are thinking about may be the bypass feature of the thermostat to relieve coolant pressure at high rev.

[Gary Yarbrough]

Thanks! I'll check both out.

I'm leaning toward the bypass feature of the thermostat b/c my leak is happening at high rev. I'd say 5500 to 6500 RPM.

[jonszr1]

there a re some therms that are for sale out there that have the wrong type of bypass feature that can cause what is happening to you , napa sells a known good type .or you can get one from randy woods at srp products. his arent cheap but they are of great quality and you can get them in 160-165-170 degrees . i use his thems in all my cars

[QB93Z]

Here is a picture of the thermostat from my 1993 ZR-1 for comparison:

http://i407.photobucket.com/albums/pp152/QB93Z/Radiator/thermostatwithwords.jpg

Jim

[secondchance]

Thanks! I'll check both out.

I'm leaning toward the bypass feature of the thermostat b/c my leak is happening at high rev. I'd say 5500 to 6500 RPM.

Keep us posted as to what you find. I am curious.

[2ZR1S]

On Friday, I spent some time trying (yet again) to troubleshoot my rough idle. I should have known better, given that it was the 13th! No luck... I was shut down early because of another issue.

I found that I have a leak in my radiator. This is the 2nd radiator to go bad in the last six months. I remember reading once that the cooling system has a pressure relief function. Can someone enlighten me on how that works and if some flaw in that system is causing my radiators to go bad? Is there something else that is likely to be causing my problems?

I destroyed a brand new Fluidyne aluminum radiator by installing an after market thermostat. $500 dollar lesson learned.....:blahblah:

[secondchance]

I destroyed a brand new Fluidyne aluminum radiator by installing an after market thermostat. $500 dollar lesson learned.....:blahblah:

Ouch! Sorry to hear that. I cracked my radiator, I suspect, for the same reason but the car had about 50,000. I got a used replacement that was pulled out of a 94 ZR-1 w/ 5,000 miles belonging to another forum member for $50!
Come to think of it, I just replaced all my rotors out of another 94 ZR-1 given to me by another forum member free!
NCRS folks, please note they are both 94 ZR-1 factory originals!!!:mrgreen:

[Hammer]

NAPA THM124 works fine. Used them in two cars now with no problem.
NAPA also has the green antifreeze required...meets 1825M spec.

[Hammer]

Another item that can blow radiators is if the thermostat wasn't installed correctly in the housing. Easy to check, but have the catch pan ready if you pull the thermostat (don't ask me how I know that). Make sure it's seated correctly. Hold it in flush with the housing, use the bracket (Marc's trick) or a putty knife while you tighten the lower housing bolt.

[Gary Yarbrough]

I finally got time to work on my leaky radiator a couple of Saturdays ago.. I replaced my thermostat with a NAPA THM124. I put on about 250 miles without really pushing the car and found that the radiator wasn't leaking. Yesterday and today, I took the car out and did about 8 7K run-ups between the two days. No leak as before. So, for now it appears that all is well.

Now, if I can just fix my dang hesitation...

[Dynomite]

I did not know you could overpressure a radiator with a wrong thermostat and centrifugal water pump.

The notch in the thermostat could not pass all the water the pump can put out at higher RPMs and I guess the centrifugal pump at high rpms would over pressure the coolant system without the bypass open. I think the notch is there in the thermostat to get hot water passing through the thermostat to cause it to initially open and then continue to open at the proper temperature.

A centrifugal water pump is not a positive displacement pump and will only put out so much pressure (depending on rpm) untill the water essentially stalls in the pump unless you have very high rpms as in the LT5. I am not sure how the overflow through the radiator cap relief if the pressure in the radiator is greater than say 15 psi (closed system) functions in this case.

The radiator cap relief opens at 15 psi and lets water pass to overflow tank and when the engine cools down the volume of water/air contracts and sucks water back into the radiator through the radiator cap (zero pressure will open the cap in reverse direction) which actually will replenish water lost by leaking.

The radiator cap for my 91' Z sits on top of the coolant black plastic container under the hood on passenger side which is pressurized and can be considered part of the radiator (not to be confused with the white plastic overflow container under the passenger side headlight).

Correct me if I am wrong :sign10:

[tomtom72]

Lotus did our cooling system specs sized to power out put paying attention to design & flow rate of the water pump. In our LT5's I think it was gallons per minute per 1000 rpms per 100 hp......or something like that. In the end the max flow from the pump ( past 5,400 rpms up to the limiter ) was way more than the stock C4 radiator could tolerate. GM was to have had another type of radiator designed & built. That never happened, instead they designed our thermostat housing & thermostat to serve a by-pass function when the flow from Lotus' water pump exceeded the radiator flow/pressure limits. Past a certain flow rate our coolant just makes a circle in & out of the block with out going thru the radiator. If it did we would blow up our OEM radiators, I guess the plastic side tanks would have been the first weak point, and then maybe the core? I know with some after market C4 radiators w/ welded metal side tanks, our water pumps with an incorrectly boxed T-stat ( wrong stat in right p/n box ) will explode the core of some of those aftermarket rads.

:cheers:
Tom