[2001 V70 2.4T] Occasional coolant reservoir boilover

[prwood]

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.

Yeah, it definitely wasn't coming back down to 190 until I turned the heat on high...

[E Showell]

I'd replace the overflow tank cap with new Volvo. Odds are your cap is leaking and the closed system doesn't properly pressurize. If coolant is mysteriously disappearing and you have white residue around the reservoir cap, I'd argue that's your problem.

If you are contemplating a thermostat replacement, get some PB Blaster or equivalent (I like Kroil because it smells so much better than PB, but is more $) on those thermostat housing bolts. They are a known corrosion point and easy to strip.

[abscate]

...and add two new bolts to that FCP thermostat order.

986228 ? You have to watch out fir a chassis break on the 2001, so order by VIN

[prwood]

I'd replace the overflow tank cap with new Volvo. Odds are your cap is leaking and the closed system doesn't properly pressurize. If coolant is mysteriously disappearing and you have white residue around the reservoir cap, I'd argue that's your problem.

I'm assuming either the Rein or Gates would be ok as they're listed as OE? FCP doesn't seem to sell a Genuine Volvo cap. The Rein is the same color as my existing cap.

https://www.fcpeuro.com/Volvo-parts/V70 ... =6&d=59&v=

[E Showell]

Both probably ok.

[prwood]

Interesting - the Rein and the Gates seem to have very different designs on the underside of the cap, even though they have the same Volvo part number:

Rein (this is what my current cap looks like):



Gates (very different design):



The size and threading seems to be the same, just the design of that part in the middle appears different. Is that the pressure valve? Wondering if one is better than the other...

[E Showell]

No experience with Gates-style cap.

[ndphotonl]

No me neither, I also replaced the tank + cap on my 2001 S80 2.4T with the "old style" cap. More for the better looks under the bonnet and peace of mind.

Volvo S80 2.4T Old vs New Coolant Expansion Tank by Andy Ramdin, on Flickr

Volvo S80 2.4T DO88.se Upper Intercooler Pipe (OTE) by Andy Ramdin, on Flickr

[prwood]

So I got the new coolant reservoir cap, and today I installed it and took the car out for a drive. This doesn't seem to have solved the problem - I ended up having the coolant boil over again once on my drive.

The coolant tank was empty before I started, so I topped it off, then I started the engine from cold and hooked up my OBD scanner and started monitoring/recording the ECT reading. Also, during most of this time I had climate control turned off to ensure that the heater wasn't dumping heat from the engine coolant and affecting the diagnosis.

Graph 1 started from home, where I headed to the highway, and drove highway for a while until I stopped at a gas station. This represents ~15 minutes of run time.

Overall things were looking good at that point. The ECT was hovering right around the thermostat temp of 195.

Graph 2 started from the gas station and ended when I drove to a fast food pickup window. This represents ~8 minutes of run time.

Things were still looking good and hovering around the thermostat temp of 195.

Graph 3 starts just after the fast food pickup, when I was idling in the parking lot. About halfway through Graph 3 (about 15:19) was when I left the parking lot to drive home, and the graph ends when I pull into the driveway. Note that I did not shut the engine off between Graph 2 and 3, the recording program I was using quit when I opened another app at the drive thru.

That means that during that gap, which would be about when I was idling with the gear in Drive in the drive thru line, the ECT temperature went up from ~194 to ~207, which is where Graph 3 starts. So after that, while I was idling in Park in the parking lot, the temperature fluctuated between ~207 and ~221. At 15:19 was when I left the parking lot and started driving again. Very shortly after that, I got the coolant lo warning message, so I pulled over, shut off the engine, and refilled the coolant. You can see this on the graph right at 15:20. After this, I turned the heat on full blast to ensure that the coolant stayed cool til I got home, and the temps dropped down.

So basically, everything looked good while I was driving from local roads to the highway (Graph 1), and everything looked good while driving on local roads, but things got bad when I was idling and reached the boiling point as I started driving again.

Given that I replaced the expansion tank cap, and given the data above, would the symptoms point to a thermostat, ECT sensor, or head gasket leak? Any thoughts what I should try next?

[MoVolvos]

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Kind of read this thread quickly but did you check to see if the fan is operating?

(EDIT: I see you said you think the fan is working. Double check as it is winter and the radiator temp could go down as you drive then back up while stopped.)

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