Leaky Radiator

[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

[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.


Tom