Yeah, I know it's not really an overflow.

Today, while resetting the knock sensor code 1-4-3 on my hot engine one more time, I noticed that my coolant bottle was empty. Strange, it was half full on Sunday when I was puttering with the car. No coolant smells anywhere.

So when I got home I let the engine cool for an hour, and gingerly released the cap JUST A LITTLE and low and behold, the coolant bubbled up and filled the bottle up halfway. WaaH???

How does the Volvo pressure system work? There is no two-stage pressure cap on the rad itself, just the one on the bottle (mine is gray, "150 KPA"). I think the lower hose is the "feed" and the upper hose is an air vent. Is there any means for pressurized coolant to vent out of the system? All I see is the cutouts in the bottle cap. But I have NEVER seen a trace of coolant escaping there.


I'm just puzzled.

 

Dear Carbuff

I had the same problem four months back. My observation was that i had to top up the coolant bottle almost on a weekly basis. So one day while i was giving coolant to its bottle (with the cold engine) i noticed small amount of coolant escaping from the O ring which is on the top of the water pump. What actually was happening, once the engine use to get hot, with the high temprature that O ring use to lock the coolant and there was no loose of coolant. may be you are also facing the same proble. So now once you are adding coolant in the bottle have a look at that O ring. It might help you out in getting to the problem.

I have 940 Turbo, automatic, model 1998

Regards

 

Thanks Qamar,

Yes I have looked all around for signs of coolant loss...as I said, no visible loss or coolant smell. The water pump o-ring is new, replaced when I did the headgasket. I was looking hard under the manifold, a hose to the heater is under there. Couldn't tell, it was getting dark.


The behavior of the coolant when I released the pressure was puzzling... on the cars I've owned the coolant level varies between MIN (cold) and MAX (hot) depending on the engine temperature. But this time the level DROPPED when hot and that's what I don't understand.

Anybody else?

 

I suppose it could be the thermostat malfunctioning, staying wide open all the time keeping more coolant inside the engine while running. Just for grins, I think I would flush out the cooling system. One of the Prestone Flush kits should be sufficient for that. See what the AF looks like when it flushes out. I know that's not a definite for your situation, but I think it is a good place to start. I'll post back in a few, hopefully with some more useful info.

 

Make sure the bottom of the coolant bottle isn't cracked and seeping from the bottom of the bottle.
It will leak down and go into the frame rail and then drip out the bottom.It will look like you spilled some.

 

Great ideas for future reference.

 

Hi Guys, Thanks.

I flushed the coolant when I had the head off in August. I had the coolant bottle off too...I like to clean them up when I change the coolant. (Difficult on the Volvo's with all those baffles in there!)

Thermostat was replaced with a Volvo one in May.

No coolant traces under the bottle but I will double check that during my travels today. Definitely no puddles under the car. I'm looking.



I'm still waiting for the answer to this question:

Where does the cooling system vent excess fluid? If it's from the cap, there was no trace at all there. Anyone ever seen those caps fail by failing to release excess pressure?

 

The only time it will come out of the cap is under very high pressure or overheating.

If you add to much yes it will come out the cap.