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Diagnostic coolant overflow

Old 07-05-2019, 02:31 AM
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Question Diagnostic coolant overflow


The car is a Volvo S80 2.4T Petrol, 2002. With the B5244 T3 engine.

I want to ask for clever ways to determent for reasons of coolant overflow from the coolant reservoir. I want to find out if the head gasket or any other gasket is for repair without open the block unnecessary.
To coolant is most of the time ok, when the car is running, the average temperature is around 90 degrees (Celsius), the thermostat is set to open around 87, so under normal load, the car is keeping 87/90 running temperature. Even in hot days - it manages to keep it up. But sometimes in traffic or high load for example highways and more than 140km/h, the temperature could reach 100+. In that case, the fans are starting to work, but the coolant is thrown from the coolant reservoir when the car is running so no longer ofter that the check coolant level error is triggered.

I made the following experiments to try to figure out what could be wrong:

- There is no visible leak of the coolant system.
- The coolant cap is working as expected it's open and close if pressure is too high.
- There is no visible oil in the coolant - currently, the car is working with 100% water - the reason is that I lose too much coolant all the time also drain the system few times - and for the test right now I keep it water only. This will be replaced with proper 50:50 antifreeze and water when I find the problem or "Winter is coming" time
- I'm not seeing bubbles in the coolant reservoir when the car is running.
- The thermostat I think is working - the temperature gauge is always in the middle. Also, I'm tracking the temperature over the OBD and it never exceeded 105.
- All my test are made with an outside temperature between 25/35 and the AIR TEMPERATURE from the OBD is around 35/45 - so it's hot outside but not that much.
- The fan starts to work when the car reaches 100. Not sure how many fan speed levels are they some say there 7 other 12. But the fan is working.
- The water pump is working fine I think - It's no more than 30 000km water pump
- The Breather Box was change
- The Crankcase Top Breather Hose and Crankcase Breather Hose Assembly line changed as well - Brand new bolts and hose clamps
- The spark plugs look clean for the time they are working.
- Had leaking coolant radiator on the top side where is connected to the hose for the thermostat. I repaired it but still running tests with that repair. Found a second hand from Volvo S60 2.0 but it was too small and could not manage to cool the temperature as fast as the big one. So for the moment, this is the reason to keep the one with the repair - Plan to replace it with brand new. Right now there is no visible leak on it. It's clean and there are no clogged paths inside.
- All hoses from the reservoir to the radiator are checked and they are in good condition. Most of the clamps are replaced with brand new.
- The coolant reservoir has no visible cracks and the plastic is in good condition. (it's old but...)

When the car throws away the coolant and the reservoir is looking empty, by opening the cap the water is pushed back to the reservoir and in that point, the car is trying to throw almost all of it before all the pressure is vented. Just then I could try to add new water. I had this few times on the road so it's something that is tricky to manage also I need to have a lot of water with me, at least 3-4liters. I know that is normal to have a lot of pressure in the system between 1 and 1.5/2 bars but still is it normal to be that high.

When the hose from the radiator to the thermostat is removed there is a lot of smoke coming from there. Not sure is it exhaust gases or water vapor. Not sure that this is normal ?! (At that point the water temperature was 87 degrees)

When the car is working there are no bubbles anywhere.

When the car is kept around 90 degrees there are no issues and no loss of coolant.

I know that the next thing to change could be the head gasket. But I want to be sure before I open it up - and this won't be unneeded repair. Also, this may not be the problem right now. Also on some forums - people are saying that the thermostat could be stuck in one of the two positions (open/close) and the needle of the gauge won't show it to mee. But also the car never exceeded 105 degrees. The sensor on top of the thermostat was cleaned and I think is working fine (not sure what exactly is doing ... presume is for the temperature at that point)

Another test that I found was to remove the spark plugs, disable the ignition and fuel pump. And try to crank it up, so could watch for bubbles at the coolant reservoir. But first of all I'm not sure that will see them because the reservoir is too far from the engine, also I could have small gasket leak so this may not be visible for a few minutes.

Old 07-05-2019, 09:15 AM
Join Date: Mar 2012
Location: Ridgefield, CT
Posts: 4,788

the coolant overflow design of these cars is not overly complex. You have a sealed system which has the coolant overflow take in parallel to the coolant line going back to the top of the radiator. Its main job is to allow the coolant to expand into the tank as it heats up. Since its a sealed system your overflow cap needs to be able to maintain a maximum system pressure but they can release pressure or coolant when the system is overfilled or the coolant overheats. So if you have scenarios where you are leaking coolant via the overflow cap, there's a few possible causes I can think of. 1) cap is old and weak and can't hold the normal pressure of a hot engine. 2) coolant system is overly full 3) radiator is clogged and not capable of providing adequate cooling capacity 4) there is a head gasket leak allowing exhaust gasses which is raising the pressure of the cooling system beyond normal. So first test would be to check if the cooling system is operating within the normal pressure range when hot enough for the fan to come on. You can also try squeezing the upper radiator hose to see if gets rock hard. If pressure is too high, next step would be to test for HCs in the coolant to see if there's a head gasket issue. If the pressure is normal, time to replace the overflow cap. Note they are color coded by pressure rating to choose what's appropriate to your model. Then I'd do a full coolant drain, distilled water flush, fill with fresh 50//50 coolant. You may still have a radiator problem but its worth investing the $50 in the cap and drain/fill to see if that helps. If you do a drain fill, that's a good time to also through in a new OEM thermostat if you are unsure of its age.
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