Random overheating, sound like an air bubble to you?

[1.8t]

Here is what is happening:

After the car has sat for a while and completely cooled off, you crank it up. Without driving it or turning the heat on you let it sit there and idle the entire time with no throttle input to let it come up to temp(takes forever in cold weather). The car comes up to temp normally and slowly continues to climb to the point of fan engagement(all normal to this point, no accelarated warm up, everything looks completely normal). The fans engage and the temp stalls for about 5~10 seconds. Then the temp slowllyy starts to climb. The fans hit their high speed engagement and the temp stalls a second time for about the same amount of time and then slowlllly continues to climb. Again, the heat is off and I have not touched the throttle at all since cranking the car. Now, obviously if I don't do something the car will eventually overheat. So, I put my foot on the throttle and bring the rpms up to 3k. After being at that rpm for maybe second or so, the coolant gauge sweeps down to operating temp in about half a second(very fast).

Once this has occurred, the car can idle all day long and it will never over heat. Turn the heat on, turn it off, give it throttle, let it idle...everytime the fans engage after I have done the above it will not even threaten to overheat. I can only assume that by giving it throttle, I am flowing a bubble from whatever location it is stuck in(possibly at the temp sensor location??), which then allows the car to function normally. This all started after I put my stock manifolds back on the car in preparation for my RSI TT kit. When I did the passenger side, I had the coolant overflow tank unbolted and contorted in all different kinds of directions to allow me to get at the manifold to head bolts. It is my assumption that this is how the air was introduced to the system as I had all lines disconnected except the overflow tank to waterpump line.

I have no over heating issues while driving under any circumstances and honestly, if I didn't let the car warm up in the fashion described above, I would never know that there was a problem. The car is a 99 GTS with the factory water pump and a 170 thermostat. To my knowledge, I have not had this problem until post manifold re-installation. Does this sound like a air bubble and subsequent bleed issue to you guys?

 

[Jack B]

air in the system or sticky thermostst

 

[denniskgb]

Sounds like a air bubble. Thermostat has a very unrestricted design.

 

[roller]

Open the bleeder plug under the thermostat housing, coolant should come out or be visible under the plug. Also check coolant level in the overflow tank that is in front of the right wheel well. Check radiator cap also if it is leaking it won't create enough vacuum to draw coolant back in from the overflow tank.

Frank

 

[Jack B]

Sounds like a air bubble. Thermostat has a very unrestricted design.

Not if it has an issue opening properly. If there is air in the coolant it is more than likely it will not be an intermittent problem/ Here is the diagnoxix:

1. Make sure the overflow bottle in the front fascia is approx half full.

2. If the bottle has adequate coolant, open the bottle on the passenger side near the headers and burp the system with the upper radiator hose. If there is air in the system it should come out this bottle. There is a full write up on the procedure on this site. It is always best to fill the system from the hose at the heater box.

3.If there is still an issue you will have to pull the thermostat to check it. There is also an outisde chance the water pump has a problem.

 

[Vital Velocity]

Make sure all the hoses going to and from the overflow and coolant bottles (passenger side bottle and front facia bottle) have clamps on them. They didn't come from the factory with them and overtime can dry up and not seal properly allowing air to be sucked into the system

 

[dave6666]

Moving that tank around could not have introduced air into the system. It could have redistributed air that was already in there, but unless you opened it up, nothing went in or out of the system that wasn't already there.

Most of this has been said so far, but as I have done lots of servicing and compete tear downs on the Gen 2 cooling system, here is my 0.02.

Make sure the line to the overflow bottle in the fascia is good, and with a clamp at the fender surge tank. The one you moved around.

Pic:

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Make sure there is coolant in the fascia overflow bottle.

Fill like this, and make note of the level:

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Remove the radiator cap on the surge tank. The tank you moved around. Make note of the level, like if it is down, but fill it to the brim regardless.

Drive the car until hot.

Then recheck the coolant level in the fascia overflow bottle. It should have gone up a bit.

If not... then you either had so much air in the system that no coolant got pushed out, or there is a leak in the hose to the fascia bottle, or the bottle itself.

When the car cools back down (at least 4 hours), assuming the above to have not been the case, then the level should return to normal. If it drops below your original starting point, that is a sign that you purged some air and the air was replaced with coolant. That is how the system is designed to work. The Gen 2 is within reason, self purging of air.

I've done many complete system drains on several cars and never once had to do any of these purge routines or fill from anywhere but the surge tank on the fender. Top off the fascia tank after a few drives and it is done.

If after all of that - you've confirmed the system is or is not operating correctly by the fascia overflow tank reactions - then proceed to looking elsewhere.

 

[alwayscode390]

Lots of great advice in this thread ---