Cooling system problems - 2003 V40 Topic is solved

[iamn8]

I keep having recurring cooling system problem with my 2003 V40. Although the temperature gauge never reads hot, it keeps puking out coolant from the top of the overflow tank on drives longer than ~15 minutes. There have been occasions where I park the car, then start to hear a bubbling from the glove box and, and when I pop the hood, the coolant starts to bubble out of the overflow cap with the engine off. Last time that happened, I started the car back up, let it idle for 2-3 minutes to circulate coolant and it stopped.

Underhood heat when I lift the hood is higher than I'd expect, particularly at the back of the engine. I'm wondering if it could be a failure in the turbo, maybe the bearing, that's causing IT to run hotter than it should. The way it's plumbed into the cooling system, there's a direct connection to the overflow, which might explain the phenomenon?

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Back story - the car's had summer cooling problems the past 3 years. It blew a head gasket in summer 2019 @ 182K miles. I replaced the gasket, decked the head, rebuilt and had no issues until summer 2020. Again, hot day in late August and the head gasket went on a highway drive. This time, I pulled the motor out and replaced it with a donor engine out of a 2004 with 113K miles on it. Back on the road last February and ran flawlessly until our first hot day in June when the overflow issue began.

At this point, every single part of the cooling system has been replaced except for the heater core. That's engine and turbo, water pump, multiple themostats, radiator and hoses. I had been blaming thermostats, and as soon as this crept up again, I completely removed this one. It's slower to heat up, but it has not resolved the problem. The top radiator hose is hotter than it had been with a thermostat in place, but again, the ECT sensor that is located in the thermostat housing is not reporting higher coolant temps than it should.

Anyway, I'm stumped. Anyone ever have an issue like this?

[RickHaleParker]

Check the pressure cap. If the coolant system is not pressurized the boiling point will be lower then the design specs.

[iamn8]

Check the pressure cap. If the coolant system is not pressurized the boiling point will be lower then the design specs.

Thank you Rick, I'm hoping this is it. I had a 0.75 bar cap on it, so I swapped to a 1.5 bar cap I had on hand this morning. I'll follow up to see if this solves it.

[iamn8]

89 degrees yesterday, got stuck in traffic for a while, no issues. 1.5 bar overflow cap was the solution. That you again Rick!!!!

Not sure why I have a 0.75 bar cap or why it was on there. Interesting that it was fine when ambient temps were low in the springtime.

[RickHaleParker]

Interesting that it was fine when ambient temps were low in the springtime.

ΔT ( the difference in temperature ) effects the rate of thermal conduction ... At higher ambient temperatures it cannot dump heat as fast because ΔT is smaller.