760 Turbo, bubbles in expansion tank?

[AndyPants]

Hi guys,

Changed the oil in my 760 (155k miles) today as although it has only done 600 miles since its last change, that was 2 years ago according to the service records.

Anyway whilst running the engine after doing the oil change I thought I'd have a look around the engine and check a few things whilst it was running. I firstly checked the dip stick to see if it was 'puffing' which it didn't seem to be, therefore I assume the engine breathers are ok (if similar to the 850s...). However when I checked the expansion tank there was the odd bubble coming up, maybe 1 a second, is this anything to worry about and does it indicate any issues with the head gasket?

Engine was up to temp, or at least it was warm/hot as my temp gauge isn't working yet (plan to give the sensor a clean). Car is not using any oil or water and there is no mayo under the filler cap. However there does seem to be a bit of oil on some of the hoses/unions to the front/left side of the engine. Car runs and drives fine.

Also I fitted a new aftermarket expansion tank cap (grey) a few months ago, listed as for a C70, as I believed they were all the same/later ones were better? Old one was cracked. I also have a spare Volvo green exp. tank cap from a S70.

Thanks.

[monkeh]

Put the green cap on, Its the now standard cap for the redblocks.
And as for the bubbles? Get the local garage to do a sniffer test on the coolant, If theres hdrocarbons in there, then its exhaust vapours, Get ready to pull the head. Not a bad job to do. It would probably be head gasket. Just make sure to get the head skimmed.

[AndyPants]

Thanks although I hope its nothing serious as it doesn't seem to be much. Put the green cap on today. I should probably also specified that I only saw the bubbles (4-5mm wide) with the cap off, its not like the tank was boiling over or the like.

The cars booked in at the garage on friday to have a look at the exhaust which is leaking/badly fitted by a kwik fit fitter... Can't imagine exhaust gasses from the exhaust itself would be to blame (possible for engine to draw them back?), but from the engine itself?

I think I'll get the temp. sensor working and once exhaust is sorted I'll closely monitor it after a few runs just to see if it was a 'glitch'. I might also try squeezing a the coolant hoses in case theres a small air lock. As I say car otherwise runs spot on (no mayo under filler cap and no oil in coolant).

P.S. like the avatar and sig lol

[CTCNetwork]

Hi,

A small stream of bubbles in the expansion tank indicate that either there may still be air in the system (Has the coolant been drain or replaced recently?) or gas escape from the engine.
Hence the suggestion for the gas test. If there are hydrocarbons present the gas test will show this and you WILL know you have a gone HG..

Des. . .

[AndyPants]

Looking at the history the water pump was removed and its gaskets/seals were replaced not that long ago, again about 600 miles ago.

I'll ask the garage to do the test when I take the car in on friday, I assume its a fairly simple test of them bunging a device into the expansion tank?

Not sure I want to know the result... lol

[CTCNetwork]

Hi,

Yes, pretty easy 5 min test. Fingers crossed.
But it is not the end of the world as doing a HG change on the red block is not too difficult to accomplish..

Des. . .

[AndyPants]

Yes fingers crossed indeed! Haven't had the car long and never had any issues with head gaskets before, however this car is old(er) and has done rather more miles! I'd be bit dissapointed though as I don't think our old 740 blew its HG and that had done well over 200k.

I imagine doing a headgasket is probably beyond my level of ability as I only do basic servicing stuff, so if it did need doing it would probably be a garage job.

I'll update this thread with the result when I know it

[CTCNetwork]

Hi,

Originally Posted by AndyPants

I imagine doing a headgasket is probably beyond my level of ability as I only do basic servicing stuff, so if it did need doing it would probably be a garage job.

Actually, not at all. Give yourself a weekend and it is surprisingly easy. Call in some help if need be.
The only thing you'd need an engineering firm for would be to check the head and do a skim if required.
Honest!

Des. . .

[AndyPants]

Well cars been to the garage, Volvo no less, and they also suspect the head gasket is going (they say the engine is over heating - car hasn't been using an coolant though or oil?) although I'm not utterly convinced they did the exhaust gas check with the exp. tank. They also pointed out that the exhaust manifold is blowing (think the chap mentioned the gaskets, which seems to match Mr. Paynes, could this or the head gasket be the source of my small oil leaks?) and they reminded me that the temp gauge doesn't work.

Looks like if I want the exhaust to fit properly I'll also probably need a new one... even more expense yay!

Up until now the cars been running spot on (as far as I could tell at least) and infact after driving from the garage, doing some shopping and coming back home there were no bubbles in the exp. tank. However after popping around to a mates and returned I opened the exp. tank and some coolant gushed out and the bubbles were coming up again, not sure whether this was because it was far too hot or just because I opened the coolant cap too quickly (its now using a 150KPA(?) S70 green cap).

Going to try and relax the rest of the weekend and avoid worrying about it too much! I tend to struggle with mechanics but the idea of making a project thread is strangely appealing but it would be a massive undertaking for me, I could however get most of if not all engine related jobs out the way though in one big go! And perhaps even change the front bumper at the same time as it could aid access.

I think my first port of call is to get that temp guage working so I can see if the engine really is overheating and if whether its the exception rather than the norm.

P.S. I looked at your Volvo 240 GLT project thread CTCNetwork and your pics are very useful in seeing how to get better access such as removing the engine fan shroud etc...

[CTCNetwork]

Hi,

Worn exhaust manifold gaskets id a fairly regular occurrence. I doubt it would cause oil leaks though.
The problem with fitting new gaskets is the fact that the bolts are likely to be well corroded onto the studs. They need to be well soaked in WD or similar.
Have a look at the FAQ:
FAQ: Exhaust Manifold Leaks...

Oil leaks are more likely to be either the cam seals or crank seals. Obviously those at the back of the engine, at the gearbox are difficult to see.

Des. . .