Began sporadically overheating. Temperature would eventually go back down.
Checked coolant and it was mostly water - Drained the radiator and added coolant, took less than a gallon
Continued sporadic problems
Replaced thermostat, was able to drive 1,000 miles
Continued sporadic problems
Replaced water pump
Continued sporadic problems
Mechanic believes it could be a small head gasket leak and recommends Blue Devil
Follow instructions cleaning, draining and refilling entire system
75 miles and it starts overheating, but consistently and can’t even get 1/2 mile
Assuming blown head gasket
Tow to mechanic, they drive it for at least 100 miles on steep inclines and can’t get it to overheat
Perform compression test - it’s good
Perform leak down test - it’s good
Start to tear apart and identify what appears to be a leak in rear heater pipes that doesn’t show because it lands on the engine and evaporates, expects the steam generated right next to sensor could be throwing false positives on overheating.
Drive 50 miles on steep inclines no overheating
I pick it up from the mechanic and 20 miles in it starts overheating. It does stay cool enough to drive it 80 miles home.
Next morning I look at the reservoir and it’s empty, look in the radiator and I can see liquid about 1 - 2 inches down.
Mechanic asks me to fill it and then see if there is air in the lines.
I fill the reservoir half way and top off the radiator and start it up. I am seeing air bubbles so I keep compressing the top hose until it appears there are no more air bubbles.
Drive the car for 20 miles and no issues, park it in the driveway to start inspecting and it begins to overheat.
Significant bubbling is occuring, but don’t know if it is from air or potentially boiling. Violent enough that it is forcing coolant out of the reservoir overflow.
Stop the car and let it sit overnight, come back to find the reservoir empty although it appeared to be 3/4 full (above the fill line) the previous night.
Start the car and watch the reservoir. I can see bubbles making their way through the small amount of liquid left in the reservoir. I add some more coolant to be able to identify more clearly and I am seeing significant bubbles and it’s too quick for it to already be boiling.
At this point I assume it’s got to be the head gasket, but that’s strange since they performed a compression and leak down test and didn’t see any issues. Also, the intermittent nature has me confused.
It is possible for a head gasket to seal adequately at the pressure used for leak-down testing (about 100 PSI) and during a compression test (100-200 PSI depending on the engine) but not during operation, especially once warmed up.
Also, if there is a hairline crack in the cylinder head, it is likely to seal when cold, and open up when warmed up. Each cylinder firing event creates a sudden impulse of pressure exceeding 2,000 PSI, which is much more than the pressure used/generated during diagnostic testing.
This is actually a problem in other industries as well. I work in heating and air conditioning, and lately there has been a rash of A/C units with leaks due to hairline cracks in copper tubing which leak only while the compressor is running–very difficult to locate and correct. If I can’t put my finger on the leak, how am I to repair it?
My advice is to use a hydrocarbon test or carbon monoxide tester to see if the gases being released through the coolant overflow contain exhaust gases or not. If the problem is a head gasket leak, there will be hydrocarbons and CO in the gases. If not, then the gases are just air and steam, which means something is causing sudden localized overheating, which could only be a defective thermostat or water pump, and you say those have already been changed.
On a car with the pressure cap on the radiator, and a non-pressurized expansion tank, a defective radiator cap will result in coolant being ejected into the tank, and not returning to the radiator upon cool-down. It generally does not result in boiling while the engine is just idling. After all, it is possible to start the engine with the radiator cap removed, in order to add coolant and purge air from the system. Eventually, as the engine warms up, the expanding coolant will result in overflowing/leakage onto the ground–not boiling.
Yeah, I was told Blue Devil was the best sealant out there and it didn’t seem to resolve the issue. Looks like a quick combustion leak test and then finding someone to repair it. Thanks everyone!!
I made mention recently of rodent damage on the fuel injector wiring of my son’s Camaro. The car had not been driven in 6 months or so. Fixed the wiring, drove it a bit, and after about 50 miles it was overheating slightly. Slightly down on coolant so topped it off, burped the air out, and all was fine. Until the next drive.
After about 75 miles the temp gauge decided to start climbing toward the top of the scale. AutoZone was a 1/4 mile away so I shut it off and coasted in to the lot. Down on coolant a lot this time.
So while letting it cool a bit I went in and bought a new cap along with coolant. Topped off coolant, replaced the radiator cap, and all is well ever since.
So I have to respectfully disagree that a cap cannot cause this kind of intermittent problem and those caps can be tested.
If you suspect a head gasket fault then try this. After the engine has sat all night loosen the radiator cap. Now retighten it and start the engine. Allow it to idle for a minute or so then loosen the cap. If you hear a hiss then a head gasket fault is likely. No hiss; the head gasket is good.
Mechanics couldn’t get it to overheat. Were they driving open roads? If it overheats on you, does it do it in stop and go driving? If so check to be sure the fan(s) are turning on when they are supposed to.
My guess is there’s a small leak in the cooling system that hasn’t been fixed yet. Don’t presume the leak is into the engine. It’s probably leaking outside the engine, but not enough to easily see. If you can get a good view of the water pump weep hole on the underside of the water pump, that’s probably the most common leak spot. I know you’ve replaced the water pump, but still worthwhile to check for a visible leak there. There’s a possibility that a new water pump is faulty, or that it is ok when installed, but quickly damaged by crud in the cooling system. Good idea to thoroughly flush the cooling system before installing a new water pump. Note that a faulty water pump might not leak while the engine is running or even immediately after it has been running, but might start to leak 4 - 12 hours later. I had this exact problem on my Corolla recently.
Has your shop pressurized the cooling system to make sure it holds pressure, and that the pressure isn’t causing obvious visible leaks? If not, that’s the next step. If it passes that test, replace the radiator cap, you might get lucky.
Experiencing a similar issue. Noticed a rough idle in a drive thru and by the time I was out the car hit the red line. Found the coolant bubbling and got it towed home. So far I’ve swapped the fan relay, which I found to be a bit burnt, and changed the coolant/thermostat. For some reason the fan won’t cycle on and I’m not sure the coolant is circulating. Taking it into the shop tomorrow for an expert’s eye. As of now, it’s been handling consistent driving but overheats if it’s left to idle. Still drives the same and the fluids seem fine. My guess is a fan/circulation issue.
