Expansion Tank Cap

[RM955I]

Bugger...it's been on and off so much recently due to flushing oil out of the cooling system (due to a failed oil cooler), that it seems to have expired.

It doesn't look as if anything has snapped but it obviously should be a single unit.

I guess I need to release any pressure and then get the old one out with pliers/mole grips or perhaps cutting a slot in it with a Dremel and drifting it out?

Any suggestions?

[cheshired5]

You can release pressure by removing the expansion tank return hose then as far as I can tell it's just a question of using whatever leverage method you can improvise to pop out the stuck cap insert.

[RM955I]

Thanks, ordered one online (they seems fairly common across many vehicles) as I couldn't get through to FRF Swansea or my local Volvo dealer.

Hopefully it will hold until the weekend (no reason for it not to if I leave the broken bit in place and screw the now detached cap back on)

[cheshired5]

Originally Posted by RM955I

Hopefully it will hold until the weekend (no reason for it not to if I leave the broken bit in place and screw the now detached cap back on)

Yes the threads of the main cap + pressure will keep it in place.
A weird failure though..... I wonder if the leaked oil weakened the bond between the cap and seal?

[RM955I]

You're probably right - that crossed my mind too.

There's still oil coming through and the cap has been on and off numerous times as I either syringe the top layer of floating oil out: or, I've had the cap off and the expansion tank out a few times and rinsed it with hot water and detergent.

I was due to give it a proper flush using dishwasher tabs (dissolve one, add it to the tank, let the car idle for 30 mins and then cool and drain...repeated 2 or 3 times; then a good rinse. I just didn't get to it as the weather was terrible at the weekend.

[Stu B]

How odd! Yes I’d go for mole grips on it once you have a nice new one ready to swap.

[cheshired5]

In my recent video here, you'll see how you can force out a decent amount of water/coolant out of the tank with a cheap tyre compressor. You then refill with water to re-establish hydraulic pressure and repeat as often as is necessary.

Much faster than syringing and I've used repeated flushes with this method to transform cooling systems contaminated with both oil and transmission fluid where the coolant radiator has split where it meets the transmission fluid chamber.

For what it's worth, I don't use any detergents for fear of fizzing up and increasing pressure in the system beyond what it's used to but that could just be me.

[RM955I]

Thanks…I’ll have a look.

I was thinking about dishwasher tabs as I saw it on another forum and it makes sense - detergent without the bubbles/lather. I’ve also seen bleach mentioned (don’t fancy that) or meths (don’t fancy that either)

As a biker I’m always conscious of anything that can attack seals (such as those in “O” ring or “X” ring chains.

[cheshired5]

Originally Posted by RM955I

As a biker I’m always conscious of anything that can attack seals (such as those in “O” ring or “X” ring chains.

Me too.
That's why I start with water only, drive around, flush out and refill with water and see how it goes.
I've never needed to use anything beyond that.

Because it's a circuit, the state of the cooling system can be found as a snapshot by looking in the expansion tank.
If that becomes oil free over time, the rest of the system will be equally clean.

[Tatsfield]

Originally Posted by RM955I

Thanks…I’ll have a look.

I was thinking about dishwasher tabs as I saw it on another forum and it makes sense - detergent without the bubbles/lather. I’ve also seen bleach mentioned (don’t fancy that) or meths (don’t fancy that either)

You're right not to want to deal with bleach. It isn't a degreaser it's a bleach. Methyl alcohol isn't a very good idea to put in the cooling system and then run it! There were cooling systems which were designed to use solvents such as ethylene glycol, the Merlin engine in WWII aircraft, but your system certainly wasn't designed for highly evaporative solvents such as meths. If you are not worried about long term damage to the hoses from using a caustic solution from a dishwasher detergent it may remove some oil but remember that the oil that these detergents were formulated to dissolve are vegetable or animal fats not high performance mineral oils. Perhaps if you were running the car on Castrol R, it might work!