Excessive Pressure on Heater Return Hose?

[Shadoobie]

Hello, I'm having some trouble with my cooling system that started with my temp gauge reading higher than usual. I wasn't too surprised since the thing has always read high, but I bought an IR temp gun just to be safe and all the temps looked normal. Yesterday I noticed that pressure was building in the cooling system and pushing coolant into the overflow, even though all the temps were still normal. I figured it was probably the radiator cap, so I bought a temporary replacement from Advance Auto while I wait for a new one from MB. Now, I don't have any pressure building up from the cap, and I can vent it from the vent lever after running and barely anything comes out. However, I have a flush tee installed on the heater return hose going into the head and that hose is venting off crazy amounts of pressure. I suspect a blown head gasket, but the car doesn't appear to be overheating anywhere (according to my temp gun), the oil and coolant both look normal with no change in level, and the exhaust isn't showing any signs of steam or coolant escaping. The only abnormality I'm noticing other than the pressure so far is that the thermostat seems to be opening slower than usual, or possibly not opening all the way. could a sticking thermostat be to blame for the issue here? Or is it a symptom of some larger problem. Let me know what you think.

[SteinOnkel]

I would go back to your friendly neighborhood Auto parts store and rent their radiator and cap test kit.

Test the cap (but if it's new it should be just fine...you never know). Then test your system. Pressurize it to whatever the cap is rated for. It should be able to hold that pressure indefinitely, if not, you've got a leak, blown head gasket etc.

Also this tool makes the refilling of the system very easy and you could remove the flushing T. It's just another point of failure.

Cheers
Steiny

[RRoller123]

Might be air caught in the system, up high where the flush fitting and head are? Might try burping it with the front end jacked up as high as you can get it. Prior to that, when the engine is cold and the car level, open that flush T and fill the remaining air space with coolant. If it takes a lot, trapped air may have been the problem. You can check it later after running to see if there has been any loss, if minor, top it of again, it may just be additional air, and repeat.

[18Fiatsandcounting]

Shadoobie, it doesn't sound to me like you have a blown head gasket; rather it sounds like you just have an overheating engine that could be the result of a stuck thermostat, fan not coming on, air pocket in the coolant passageways, etc. I'll have to play around with my IR thermometer, but my guess is that the outside of the engine might appear OK with an IR thermometer while the coolant inside was hotter than it should be. It only takes 10 or 20 degrees above normal to start getting into trouble, with resultant pressure increases.

Try the suggestions above from Steiny and RRoller and see what you learn. Good luck.

-Bryan

[Shadoobie]

Thanks for your suggestions everyone. I started with the radiator pressure test, and I found a very small coolant leak coming from my flush tee. I tightened the clamp and ran the test again, and I still seemed to be losing pressure at about half a psi over 5 minutes. To be fair, though, the closest adapter I got in the kit was too small to screw down onto the radiator neck, but the rubber stopper was the perfect size to seal the system off, so I'm not sure how to feel about that test. Next, I topped off the system from my flush tee and stuck a funnel in it, then I ran the engine with the system open and the funnel quite high so that I could make sure that I got every bit of air that I possibly could. I also have my heater core set to fully open.

From this point, some strange things started to happen. First off, the coolant level dropped pretty sharply when the engine came on. Then it slowly returned as a thick foam. After a few minutes, the foam turned into a stream of bubbles, and then it slowed down to an inconsistent but near constant bubbling. It eventually evened out pretty well with occasional bubbles and all of the temperatures seemed pretty normal. However, as soon as the thermostat reached 180 degrees, I noticed that it wouldn't open up, but all the other hoses jumped by 10-15 degrees and the coolant started to very quickly rise to the top of the funnel, so I cut the car off. As soon as I cut the car off, though, all of the coolant very quickly swelled up, then sucked back into the tee and well below it, so much so that I could no longer see any coolant in there, but it wasnt draining into the overflow tank. Thoughts?

[18Fiatsandcounting]

Well, you have me worried here with your observation of bubbles and foaming in the coolant, so maybe there is a leak somewhere in the head gasket? Perhaps not between the oil passageways and the coolant, but between a combustion cylinder and coolant?

However, let's not assume the worst for now. Try this test: With the engine totally cold and filled up with coolant as best you can from both the radiator fill cap and T-connection, put the radiator cap and T-connection cap back on and tighten. Start the engine. Within a minute or two, the short curved coolant hose that goes from the top front of the engine to the thermostat should start to warm. The radiator and the two hoses that connect to it at the top and bottom should still be cold. The short curved coolant hose should continue to get warmer as the engine runs.

When the thermostat opens after 5 or 10 minutes, and this should happen around 180 to 200 oF if your temp gauge is accurate, the radiator and its 2 hoses should start to warm in this order: First, the top radiator hose. Second, the top of the radiator, and then slowly (over a minute or so) warming also to the bottom of the radiator. Finally, the hose that goes from the bottom of the radiator to the thermostat bottom connection should warm up. At this point, the engine should be pretty much fully warmed up, and the whole process should have taken 5 to 15 minutes depending on how cold it is where you are.

Use caution when feeling hose temperatures when the engine is running, of course.

If the hoses don't heat up in the order described above, possibilities are a bad thermostat, a partially blocked radiator, or a big air pocket somewhere around the thermostat.

One other question: Does your radiator fan ever come on?

-Bryan