Weird cooling issue: Puking cold coolant

[MTBSully]

I recently picked up an 03 cobra that has a weird cooling issue. It will puke coolant out the radiator overflow reservoir (aftermarket canton or similar). However, the coolant it pukes is cold, almost like the thermostat is not opening. I removed the thermostat, it is an aftermarket "Motorad" one. Put it in a pot of boiling water and it seemed to open ok, reinstalled it, filled and burped according to the Reisch page, and it still puked cold coolant after 20 or so minutes of idling.

I rented a cooling system pressure tester and pressurized from the reservoir cap 15PSI. 20 minutes later pressure had not dropped at all so I assume tank and radiator are good. Fearing a head gasket issue I also bought one of those "block tester" kits that tests for exhaust gases in the coolant. I checked at both the coolant crossover and the expansion tank, no change in fluid color, so there does not appear to be any exhaust in the coolant.

I also did a compression test and all readings were healthy ~160PSI all within 10PSI of each other.

Kind of stumped at this point. Im going to try a stock reservoir and probably throw in a new OEM thermostat and try burping again. Should I possibly try running with no thermostat to see if that helps? Just seems to me that if it is puking cold coolant, I dont have any flow through the radiator. Anything else anyone can think of? Maybe a stubborn air pocket somewhere?

 

[1wild-horse]

Air pocket would be first guess. Did you happen to check the rad cap to see if it holds? Cooling systems do some weird shit sometimes when they can't make pressure .

 

[01yellercobra]

I second checking the cap. You might luck out on it being that simple.

 

[MTBSully]

Air pocket would be first guess. Did you happen to check the rad cap to see if it holds? Cooling systems do some weird shit sometimes when they can't make pressure .

I pulled the vent line off of the reservoir (small one that goes to the radiator) and applied compressed air at about 10-15PSI and did not hear any leaking.

Im going to try a stock reservoir, cap and a new thermostat today. Hopefully make some progress

 

[P49Y-CY]

Does the coolant appear after you drive and the car is hot?

 

[MTBSully]

Does the coolant appear after you drive and the car is hot?

Yes, does not puke coolant until the car is warm (temp gauge about the middle). Still, the coolant it pukes is ambient temp, or cold.

 

[VA-Mach1]

Air.

 

[Boss75]

I had this exact issue on my Cobra recently. I filled and burped from the coolant crossover tube and solved all my coolant issues. I'd give that a shot first. It's cheap and just takes a little time.

 

[97snakebite]

expanding coolant has to go some where

 

[hotcobra03]

I had this issue..for me after all of those test you did,and confirm fan was right..

radiator..

installed new and no issues..

my last test..was run garden hose into front of radiator..doing this I didn't puk

 

[MTBSully]

Last night I installed a new thermostat from advance auto (Carquest 180 degree). It was a different design than the one that was in there, and in hot water on the stove top it appeared to open much sooner than the "motorad" one that came out. I also for shits and giggles installed a stock expansion tank. I then went through the bleeding procedure and eventually felt warm water coming through the bottom hose of the radiator. Once the car reached 86C ( ~185F, i used the instrument cluster readout), the fans came on and it never got any hotter. Shut the car down, and the coolant level in the funnel at the crossver started to drop which has never worked for me before, but is normal.

An hour later I took the car for a short drive and again the car never got over 86C. I'm hoping the incorrect or faulty thermostat was all it was. After work today I will double check the coolant levels and take it for a longer drive and report back.

 

[MTBSully]

Took for a 20 minute drive yesterday. got into boost a few times. Highest I saw the temp get was 195F according to the factory sending unit. Car definitely has aftermarket fan settings. Idling in the driveway after the drive the temp got down to 172-174 and stayed. Not a single drip of puking from the overflow tank. I think we are good to go now!

 

[01yellercobra]

Glad to hear you figured it out.