Overheating troubleshooting

[Jpalatinus]

I drove 6808 to work yesterday and after about 10 miles driving with ac on i note the temperature was 240 and and steam was coming out of the back. I quickly shut her off and parked. She has never overheated before i drove to las vegas for d weekend in october without a problem. I had her towed home i added coolant and bleed the system in my garage. There were no visible leaks the cooling fans came on at about 180 and turned off at 160 and the temperature stayed nominal at idle with the front end facing my garage wall. I decided to take her for a drive and after driving .25 miles at slow speed the temp again began to climb over 220. Interestingly i noted the fans didnt come on so i suspected an otterstat issue, i did try to open the bleeder valve at this point and it pissed like an aircompressor it seemed that the coolant was boiled in the gas phase. So i shut her off let her cool down jumped the otterstat, confirmed that both fans were on continuously and i bled the air out of the radiator (there appeared to be none) and the thermostat a few small bubbles. The temperature stayed stable at idle, but i gave it 3 soft revs of the pedal and is began to climb higher than 220 again. I had a hose still on the bleeder valve and decided to open it just above 220 it started to piss like an air compressor, which i think was the collant in the gas phase and not as a product from being too hot. The water pump appears to be turning normally and the battery voltage stays above 13v. The belt is tight and new.

I am suspecting the thermostat is stuck or perhaps intermittently stuck. In the past i have found most overheating issues could be solved by confirming the fans were running and bleeding out air. Any suggestions for further troubleshooting?

Joe p
6808
17167
883

[Helirich]

Sounds like you got it figured. I would think it pretty much has to be the thermostat or the water pump with the stat being more likely.

[David T]

No harm in checking the thermostat but now it sounds like you have "popped" a head gasket if you keep getting air (gasses) in the cooling system. A combustion gas test is in order now. Make sure the fans are cycling on the "O" switch and NOT the circuit breaker.

[Ethan Rode]

Hi Joe,

I remember you from D Weekend.

There should be no air at all in the cooling system, aside from the coolant tank. Coolant should only enter gas phase in the coolant tank when the cap opens to relieve pressure, if there's a leak, or a blown head gasket.

Sounds like you may have two separate issues:
-Intermittent failure of the cooling fan to activate
-Cooling system has a leak somewhere

I'd recommend pressure testing the cooling system. If you don't have a cooling system pressure tester, you can borrow one from Auto Zone or O'Reilly's. The system should hold 15psi for at least 15min. You can even bleed the system with the tester. Even a slight drip can cause the issues you describe. A stuck thermostat is certainly a possibility, although I'd check for leaks first.

[Jpalatinus]

Thanks for the comments i grabbed a combustion gas analyzer and went to town sucking the coolant vapor through from the expansion bottle and saw no color change in the bottle i allowed it to get to 220 and then had to shut it off 2/2 to temperature. I then grabbed the pressure tester and pumped to 15, initially it dropped to about 14 after 10 minutes and i thought Ethan was right bit then i realized i hadnt tightened the bleeder screw all the way, now it held 15 psi on the money for 15 minutes.

So no leak and no head gasket pop at least i hope is the conclusion here.

I did make an an aditional observation. My other car 17167 has continuous brisk flow from the heater hose to the expansions tank as soon as you turn the car on.

When i start this car, The heater hose exhibits no flow., there is no coolant flow to the expansion tank from this hose at all does this suggest the culprit lesion?

I appreciate the input!
Joe p

[Jpalatinus]

Also i now think the otterstat switch itself is functional i noted this time as it came up to temperature the coolant pipe where the otterstat sits was actually cool to the touch despite the engine temperature being greater than 220.

I guess are any other tests merrited, or given this is it reasonable to just replace the water pump? To me now it seems to be a coolant flow issue I replaced it about 10 years ago and 2k miles ago for a small coolant leak in valley at the time just figured if i was going in might as well do it all. Could a stuck thermostat alone explain my predicament?

[Ethan Rode]

If the otterstat pipe was cool to the touch, it would seem logical that the thermostat is stuck closed. Maybe replace the thermostat before going after the water pump. The pump usually only fails at the mechanical seal, not at the impeller.

[Bitsyncmaster]

If the otterstat pipe was cool to the touch, it would seem logical that the thermostat is stuck closed. Maybe replace the thermostat before going after the water pump. The pump usually only fails at the mechanical seal, not at the impeller.

+1
95% chance it's just the thermostat.

[82DMC12]

You can also be doubly-sure you didn't blow a head gasket if you let the car sit all night and then when cold, pull out the oil drain plug for a couple seconds and see if any water/coolant comes out. It will sink to the bottom and be the first thing to come out if you have a blown head gasket. If you're quick you can put the drain plug back in without draining the whole crankcase.

I bought a cooling system pressure tester at NAPA because I couldn't find one that actually works reliably for rental near my house. It's a good tool to have in the garage especially when you are doing cooling system work since you'll probably open the system up a few times while working on it.

[Jpalatinus]

Thanks
im due to change the oil as well so i will check that, though the car runs great and no white smoke in exhaust etc. And no detectable exhaust gas in coolant i am always scared when i overheat that i blew a hg but fortunately i think thats ok.

I got a thermostat from delorean go today and replaced it. Put it back together and pressure tested and bled the system so far no more overheating i drove about 3 miles and let it idle in my garage.

Im kinda surprised that worked. There was not gunk or anything on the old one. I was expecting to find something obviously clogged or visibly stuck. The spring seemed a little stiffer in the old thermostat then the new one, but both easy to compresss with fingers in one hand. Anyway thanks for the input!
Joe p.