Here's a quick check my local Volvo indie taught me to see if the head gasket is behind the coolant rise. It works well for our red block engines and he did it on my 940 to confirm our supicions it was a slow head gasket leak. Remove the expansion tank cap. Warm the engine fully. Within a few minutes, like right around the time the thermostat would normally open, maybe even a bit sooner, if the coolant suddenly rises looking like it's about to have a sudden boil over then you've likely got a leak. The hot exhaust gases hasten the sudden rise. A normal engine should be able to run much longer before reaching any kind of boil over and in fact many of our engines can idle almost indefinitely without a boil over. I was suprised how well that worked.

Note that increased pressure will help find the weak points in any coolant system. For me, it was the unsecured top rad plug followed by the failure of an old heater valve hose followed by the failure of a releatively new heater valve. This was all before the rad cap could open enough to release the sudden rise in pressure. In your case it may be that oil cooler hose. In the worst case it's the heater core. You absolutely don't want to risk a warped head by getting to the stage of a sudden escape of fluid and the engine running dry so do keep an eye on things and pack extra fluid until you're sure that cracked hose was the only problem. With luck that's all it is, just be warned to keep an extra close eye on the coolant system for the next while, like popping the hood at the end of every run.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Thanks for all the excellent advice.

Just did some crawling around under the volvo and have now replaced the oil cooler water hoses (i had spares) that fit onto the oil filter base (its a turbo). One of them was very crusty and let water out if you squeezed it. A truly horrible cramped little job on a cold day. Kerbside autos!

Noticed a trail of coolant on the ground where we’d pulled away earlier which was the first good clue we’d had on this one as this is the first day for ages that the road has been dry. And could see coolant dripping out at a fair rate with the engine running. Turned off and flow stopped. Interestingly couldn't replicate the problem though, perhaps it needed to build up enough pressure again before it got through pinholes in the hose.

Have refilled with fresh coolant and topped up just now so fingers crossed. Will continue monitoring levels as could still be more leaks. Running a 30% antifreeze/water mix. The old stuff i drained out was pretty clean. Had a good butchers at the heater vac switch, looked all ok, all dry on the joints - may replace anyway sooner rather than later.

I might fit fit a pressure indicator iin the pipework as a project. You can’t have too much telemetry.

Regards

"I checked the water and found none in the header" -- by 'header' do you mean the coolant reservoir? And when you say "none".....

"...the level rises as it warms up from the min to almost the max..." .....trying to reconcile "none" with "up from the min". So, when cold, is there no coolant at all in the reservoir or is it at the minimum level? Your comments seem to be in conflict on that point.

Every car I've ever had with a pressurized reservoir behaves exactly as you've described. When cold, the reservoir sits at the "min" level in the reservoir. When fully warmed up, it sits at or near the "max" level. If you fill it cold to the max level, it will spit out the added coolant - because there's no room for it. Coolant expands about 4-6% in volume when heated from ambient to something close to boiling point, depending on how much antifreeze, the type, etc. So, a 2 gallon system becomes closer to 2 gallons and 10-16 ozs. That's the rise you see in the reservoir.

So - if your concern is the movement between max and min when hot and cold -- completely normal. You should have a concern if the level drops below the min when cold. Then, you're loosing coolant.

Dear Pierso,

"Before going on a 50 mile drive the other day I checked the water and found none in the header. Cant see any drips, leaks or anything obvious so am now a little worried."
--> Do you use original coolant? Volvo OE coolant leaves white deposit at slow leak points. I'm not sure about aftermarket coolants.


"while it was warming up just now and notice that the level rises as it warms up from the min to almost the max"
--> This happens when radiator cap is loose or leaks. Check that the cap is tight. If you examine carefully you'll notice that Volvo cap was designed without any rubber sealing gasket (it uses plastic to plastic seal). If cap still leaks when tight then you might need a new cap or maybe put a DIY gasket in there.


How old is the radiator? The plastic housings (crimped to both ends of radiator fins) seals might leak after 10 years or more. Cracks might develop at the plastic ports of hose attachments - cracks could be beneath the hose too. These plastics do get brittle with age. Removing hoses to check for cracks is a risky move so proceed carefully. Suggest to replace any old radiator as cheap insurance against engine damage. Check also for any coolant puddle on front undercarriage pan beneath the waterpump's weep hole. Weep hole usually leaks when engine is off (cooling period).

Amarin.

Pressure tester.
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Post Back. That's whats makes this forum work.

Dear pierso,

Hope you're well. When were the heater and radiator hoses last changed? If it is more than 15 years, those hoses are "on borrowed time".

A "pin-hole" leak can spray coolant, which promptly evaporates, leaving no obvious signs.

Heater hoses are hard to inspect, being tucked-away at a rear corner of the engine. For other hoses, wrapping them in plain white paper towels will reveal a pin-hole leak: even if the coolant is gone, the paper will no longer be white.

Please post-back with your findings.

Hope this helps.

Yours faithfully,

Spook