Hi, I have an engine overheating issue. Not quite sure how to troubleshoot.

Here are my observations:

1. While driving, noticed engine temperate needle climbing above 3'oclock.
2. Pulled over straight away. Cut the engine.
3. Popped the bonnet to notice water spillage around the lid of an empty radiator expansion tank
4. I waited 3 hours, refilled the radiator expansion tank with water, noticing no leaks on the road below and no milky liquid from the oil dipstick
5. Drove roughly 10 minutes before the needle began to climb again.
6. Pulled over straight away. Cut the engine.
7. Popped the bonnet to notice water spillage around the lid of an empty radiator expansion tank (again)
8. Purchased another radiator expansion cap and replaced the old (possible failed gasket or over pressurized due to heat?)
9. Refilled the radiator expansion tank with water and took the car for another test drive
10. Car began to overheat after 10 minutes of driving
11. Pulled over, cut the engine, popped the bonnet noticing expansion tank at the appropriate water level with no water leakage around cap this time

Any ideas what may be causing this?

 

Yes, an over pressurized cooling system from a damaged head gasket that is allowing combustion gasses into the cooling system. It is true some cars get milky oil with a blown head gasket but in a volvo the oil return galleys are too far from the coolant galleys for the two to mix.

Use a chemical head gasket detector - the tool takes a sample of the air in the coolant bottle, and tests for unburnt gas. Or if bad enough you can use a radiator pressure tester and note how unusually fast and high the pressure becomes.

I trust your cooling fan is working and hot air is being expelled from the radiator (meaning the thermostat is opening and allowing coolant to flow).

 

Or the simplest way to confirm is to just run the motor at idle and see how fast pressure builds up in the coolant hoses.They will get rock hard fast, a few minutes. By what you are describing pretty sure it's a blown HG.

 

Yes. The engine fan has switched on after about 25 minutes with engine idling in driveway (no engine revs). The needle began to climb slowly from the 3'oclock position at about 28 minutes. This would suggest the thermostat is also functional (whether at 93C I cannot confirm without knowing what the water temperature is).

When I'm driving the vehicle I have no loss of power or misfiring which I've also read is common with a failed heard gasket.

In addition to this, I can hear the water gushing around from behind the dashboard when accelerating (parked) which could be air inside the cooling system. I'll try bleeding the air out and see if this does anything.

Thanks for your help.