Hey Volvo Forums, I've been on the forums for a while and could use some help. My coolant reservoir on the 92 940 has begun to overflow from the cap; this is the stock grey cap that I am replacing later today with an aftermarket green cap. I checked for bubbles in the reservoir/around the surrounding hoses while the car was running, didn't see bubbles or leaks. I checked the upper and lower radiator hoses which was replaced last year, and both were still good. I also don't see oil in the coolant/coolant in the oil, so I don't think I have a blown head gasket but I'm not ruling anything out. The car hasn't overheated, and I always look to the gauge when I drive.

The first time the reservoir overflowed was yesterday. The level was between the mid and max line. I drove the car for about twenty minutes, parked, and could smell coolant as I walked from my car. This is when I saw coolant seeping from the reservoir and by the time I got back to my car a few hours later, the tank was completely empty. I added whatever coolant I had left, which brought the tank up to the minimum line. I drove the car home, another twenty minutes, and the reservoir overflowed again when I parked. I've heard that the original caps can fail and cause overflow. I'm holding out hope that when I replace the cap my problem will be fixed, but does anyone have advice on other things I can check while I wait for the part?

 

The relief valve pressure in green and grey/black caps are different. Yes they do fail the relief valve falls apart or the cap cracks. Usually pretty obvious but I still own a cap tester - that"s the best way to know - maybe your local auto parts has a loaner cap tester tool or you can take it into the store.

If the cap is not holding pressure - it can overheat - and with the slow "let's not freak out the consumer" gauge - you might not get an indication until it's overheating badly. Also the reservoirs crack and leak - there again easily found with a radiator pressure tester - maybe a loaner tool for that.

I've seen a loaner chemical head gasket tester on my local auto parts website -

The grey/black caps 1357775 - release at 75 kpa

The green caps 9445462 - release at 150 kpa

Parts catalog specifies the green cap for your car.

 

Thank you-I'll head over to my parts store and see if they can lend me one of those testers. I have seen green and black caps, and both have the same rating of 150 kpa. My stock cap is rated at 100 kpa. Even the green and black caps on rockauto and ipd are the same. I have found a black cap at 75 kpa, but ipd says it only fits the 200 series cars. Besides the color, is there any difference between the caps? If I could get my hands on a lower rated cap I will, but I haven't seen one on the stores I usually buy parts from.

 

You need the higher rated cap - the green one. Higher pressure in the system raises the boiling point.

 

Had this on my 99 V70R, It turned out to be one speed of the fan not working so it didn't cool the engine when it had stopped,

 

Make sure the feed hose to the radiator is hot when the engine is warm. If not, your thermostat is stuck closed and the coolant is backing up.