[2001 V70 2.4T] Occasional coolant reservoir boilover

[prwood]

Hello friends, long time no post. Hope you are all safe and healthy. I've been working from home since March, and my family also acquired a minivan from a relative which we use for family drives, so the old TARDIS hasn't been driven as much as usual. Nonetheless, it seems to have developed a new problem.

Occasionally when I start up the car, I get the "coolant level low, stop engine" message. Each time when I check, the level of coolant in the reservoir is all the way down at the bottom, and I can see clear signs of coolant spray - white residue in the area of the coolant reservoir. I can also see that coolant has puddled and dripped down on the subframe next to the right front wheel. Initially I thought there might have been a coolant leak somewhere, so after topping off, I ran the engine until it was up to temperature and checked for leaks, but didn't see any issues in any of the hoses or connection points in the cooling system. I even took the timing belt cover off to check for any leaks in the water pump - everything is clean. I've monitored the ECT sensor while driving, and the temperatures seem to be in the normal range, oscillating between 195-220F. One thing I've noticed is that the coolant low alert never happens while I'm driving - it's only when I start the car. I've actually had it happen a couple of times where I start the car normally, drive to an errand, shut it off, and when I come back out to start it up, the coolant level is low. As best I can tell, it seems like at some point between me shutting off the engine and leaving the car, and me getting back to the car, the coolant is boiling over and draining the reservoir.

In the past I have had similar issues if the engine cooling fan has failed or the ECT sensor has failed; however I checked the fan and it is coming on properly (I think) when the engine temp is up to 215+, and driving the temperature back down. The ECT sensor is also giving what seem like sensible readings over the OBD diagnostic tools.

I also thought that perhaps some air had gotten into the cooling system, so I tried running the car for a while with the reservoir lid open and the heater on for a while, monitoring the coolant level, and topping it off so as to "burp" the system (even though I've read that this is unnecessary with these cars, I thought what the heck). Later on, however, the coolant boiled over again, so I don't think that was the issue.

Although I don't drive it nearly as much, I do try to drive it every few days for local errands and such, and sometimes it can go for a week or two before the coolant issue comes back. I have taken to just carrying a jug of premixed coolant in the car and refilling it when needed. However, I'd like to get back to a place where I don't need to do this. I'd be happy to hear any suggestions for further diagnostics or possible causes of this type of problem.

[93SCMax]

I believe you still have air in the system, and I don't believe opening the reservoir lid will purge it.

Just a suggestion, jack up the front of the car, remove the cap on the radiator and then start it. Let it idle and warm up, possibly forcing the air to the top (highest point would be radiator cap). Add coolant to the reservoir as needed. You can watch to see if the system burps.

If you can't jack it up, park on a steep hill, nose facing upward.

Good luck.

[prwood]

I believe you still have air in the system, and I don't believe opening the reservoir lid will purge it.

Just a suggestion, jack up the front of the car, remove the cap on the radiator and then start it. Let it idle and warm up, possibly forcing the air to the top (highest point would be radiator cap). Add coolant to the reservoir as needed. You can watch to see if the system burps.

If you can't jack it up, park on a steep hill, nose facing upward.

Good luck.

Just to clarify, this model doesn't have a cap on the radiator, just on the reservoir. I can jack it up or put it on ramps, but would this still work if I just took the reservoir cap off, with no cap to take off on the radiator?

[93SCMax]

I apologize...my mistake. I was thinking of how I've purged air from my other cars.

I suspect that if you leave the cap off you will just have a boil over once hot (as you've already experienced). I believe the 2001 V70 cooling system is a closed system and pressurized. Are you confident that the Coolant Reservoir Cap seals the system?

Since you only experience the boil over after the car has been shut down, it indicates to me that the coolant is too hot at shutdown. I thought most thermostats open at 90-92 degs C. If you are running 215 degs F plus, that may be an indicator. When was the last time the thermostat was replaced? When was the last time the Coolant Temperature Sensor was replaced? Were they Volvo components?

Is it possible you have a cylinder head leak and are getting exhaust gases into the cooling system? Once the engine is up to temp, have you checked the exhaust pipe for signs of burned coolant...a sweet smell out the exhaust?

Hope these suggestions help. Maybe someone who's actually experienced what you are going thru will chime in.

Good luck.

[prwood]

I suspect that if you leave the cap off you will just have a boil over once hot (as you've already experienced). I believe the 2001 V70 cooling system is a closed system and pressurized. Are you confident that the Coolant Reservoir Cap seals the system?

I guess I wouldn't say that I'm confident. It's obviously not 100% sealed, since coolant can boil out from under the cap as opposed to exploding the reservoir. I'm not sure how to tell if it's properly sealed.

Since you only experience the boil over after the car has been shut down, it indicates to me that the coolant is too hot at shutdown. I thought most thermostats open at 90-92 degs C. If you are running 215 degs F plus, that may be an indicator. When was the last time the thermostat was replaced? When was the last time the Coolant Temperature Sensor was replaced? Were they Volvo components?

I replaced the thermostat and ECT sensor in 2017. The thermostat model I used is designed to open at 195F. I've put about 50,000 miles on the car since then and I don't believe I've replaced either of them since that time. It seems like the ECT sensor is still giving good readings, at least based on what I'm reading from my OBD scanner. If the coolant is too hot, that seems like the thermostat might not be opening, which seems strange, since I thought thermostats were designed to fail in the open position? I might be mistaken. Maybe it's time to replace the thermostat?

Is it possible you have a cylinder head leak and are getting exhaust gases into the cooling system? Once the engine is up to temp, have you checked the exhaust pipe for signs of burned coolant...a sweet smell out the exhaust?

It's certainly possible... the car has 262k+ miles on it and the engine hasn't always been run under the best conditions. I'll check for the smell the next time I'm out there.

[jonesg]

Hi Peter,
try this, when the engine is cold, open the exp cap, if its under pressure its a sign the exh gas is pressurizing the system.

If so , then get some block tester fluid from autozone (they have a free loaner test kit) and follow the tests indicated, it will change color if there is exh gasses present.

[prwood]

I actually did the block test back in 2017 while diagnosing a similar coolant issue (turned out to be an improperly tightened radiator hose back then):

viewtopic.php?f=9&t=81752

It came back negative at that point, but it's possible things have gotten worse in the intervening 50k miles since then. I actually still have the fluid that I had to buy to go with the kit, does anyone know if that stuff expires or if it should still be usable 3 years later? I checked local AutoZones and none of them have the tester available, will have to check Advance or O'Reilly.

[jonesg]

If you have a spare pressure cap just drill a hole, insert a tube above the coolant and immerse the other end into a bottle with some test fluid,
the gas will bubble through the liquid and indicate.

[prwood]

So today I drove around a bit with my iPhone's OBD scanner running a graph of the ECT reading. The temperature trends pretty steadily upwards towards 200F, goes over 200F, up to 220F, then back down a bit, but always hovers in the 200-205F range. HOWEVER - if I switch climate control to max heat and max fan, the temperature IMMEDIATELY drops down to 195, 190, 187F and climate control blasts hot air. This makes me think that maybe the thermostat is the issue, if the heater core is able to cool the fluid to a reasonable temperature, maybe the fluid is never getting to the radiator. If I recall correctly from 3 years ago, the thermostat on this model is pretty easy to access:

Thermostat Location

Also, regarding thermostats, I notice that FCP has several models available with several different temperatures: 87C, 90C, and 92C. The Genuine Volvo one is 90C. The aftermarket one I installed in 2017 was 195F which is 90C. Not sure if there would be any value in using one with a higher or lower temperature.

As for diagnosing a possible head gasket leak: I don't have a spare reservoir cap to do a makeshift block test kit. It does look like my local O'Reilly has the test kit available for loan, so I may give that a try. I didn't notice a sweet smell from the exhaust when I was walking around the car today, but I also didn't go sticking my face in exhaust fumes... not sure how noticeable it would have been from standing a few feet away.

[abscate]

If you are in the mid 30F temp ambient your coolant temp should be sitting at the thermostat temp for your turbo, that’s about 190Fm in the summer at idle it will cycle up to about 205F before the fan comes in and brings it back to 190, but that cycling is normal.