Practically Classics Forum

Here is something to think on!

There is no visable way of the car coping with the increase in pressure
when the coolant heats up and expands. It has a simple screw cap on
the expansion tank. This lack of being able to breath is one possible
reason that the seal on the water pump went previously and why there
is now a leak from the radiator.



On most modern cars the filler cap is spring loaded so when the water
pressure gets too high the pressure pushes the spring up and the excess
water goes to the expansion tank. This is because the coolant system
operates under pressure and has ways of dealing with it.

Example of that type of coolant filler cap.



With older cars they don't operate under the same pressure so there is a
breather hole to allow the air to expel when the water expands, and allows
air into the tank when the water contracts.

The Volvo V70 t5 looks like an old style coolant system at first glance, but
it isn't, so what the hell am I missing?

Why has this car got it's current problems?

Well starting with the pressure cap, the correct one for your Mother's car should look something like this:

That looks like whats on there.

Good, so assuming it's ok then maybe there's some excess pressure in the cooling system? This could be something as simple as a bad thermostat, the usual water pump impeller problem or a fan not cutting in but I'd also be having a CO test done at the filler opening with the engine hot after it's just completed a run. Any sign of gas there means that the HG's starting to let go and these can warp their heads spectacularly if they're not sorted long before they actually overheat.

I'm not sure it's possible for these modern pressure caps to fail closed, if that cap were the cause of the fault, it would fail open so the coolant would boil at a much lower temperature and would escape, but usually past the cap itself.

I know absolutely nothing about Volvos in any shape or form, but it will have an expansion tank somewhere. My guess is if you can't physically see one it could be built into the body of the radiator, as was common on PSA cars (various Citroens\Peugeots) during the 80's and 90's. Or, alternatively, check a Volvo manual!

Update- it's not in the rad, do an image search of 'v70 expansion tank' so you know what you're looking for.

I have noticed that the filler cap looks like it is solid and no spring in sight.
And after driving to Durham Currys to get mother a new printer there was
steam coming from the radiator till I unscrewed the filler cap on the
expansion tank and released the pressure.

There isn't a spring in these modern caps. It's simply a rubber disc that deforms under pressure to allow the system to blow off. Much like the one in a pressure cooker but without the lead ball.
There's obviously a leak somewhere that's allowing the coolant to turn to steam as soon as it's depressurised which is what it would do as it'll then boil at 100C, find and fix the radiator leak first, then see where you are with it.

John the radiator never leaked before, so assuming that there is a fault
which is causing the coolant tank be unable to cope with the expansion
of the water, and air in the tank.

The seal on the water pump went first as it was the weakest, then since
that was fixed it went for the next weak point the radiator.

I have noticed what could be a design flaw in the cooling system, even
mother noticed it!

The top radiator pipe arks up over and I have squeezed it when refilling the
coolant to get rid of trapped air.

OK chaps, I've got one of these motors and have done a large amount of work on it, so I think I know the car pretty well, so let's sort this out:

Mitsuru - the system is supposed to be pressurised, that's what stops the coolant boiling. No, in my experience (which is considerable) many modern cars don't have spring-loaded pressure caps (although some still do), they have systems just like the Volvo, with an expansion tank. The clue is in the word "expansion". As John says, the cap to this tank will release excess pressure in the event of a fault.

That means that if you're not loosing coolant through the pressure cap, and the pressure cap is OK (they rarely fail closed, and are cheap to replace) then the system is not over-pressurising. If you want to be double sure then get a sniff test done, but head gaskets rarely go on these and cracked blocks/heads are virtually unknown.

I would put a large amount of money on there being nothing wrong with the coolant pressure. You had a water pump go - big deal, yes, they do fail, if it wasn't changed the last time the cam belt was done then it's about due to fail, they are pretty much service items in these cars (as well as most modern cars these days). Same with the radiator, if it's the original one then it's done very well to survive this long, they do go after a while, again they are almost service items, every 100k or so. The reason there's steam coming from it is that it's leaking, so just get on with it and get it replaced. Check if it's leaked coolant into either the engine oil or the transmission oil, as the coolers for these are integrated with the rad. If it's engine oil, then you'll need to change this, if it's transmission oil then you'll need to get a professional to flush the system fully, although if you've driven the car like this for very far then you will have lunched the autobox by now.

No, you haven't spotted a design fault, sorry to disappoint you but Volvo are probably a little bit better than you are at designing cars. The system never traps air in the cooling pipes, it doesn't even need bleed points, it's totally self bleeding, although from an empty fill it might need a couple of hot/cold cycles to fully bleed. You don't need to bleed it, just fill it and drive it, and top it up afterwards.

And finally I do think you're posting in the wrong forum. I don't want to raise the age-old argument about what is a classic, but I think it's fair to say that a 1997 Volvo V70 isn't one - by a very long shot IMO, that's why I don't post about mine here.

Hope that helps.

John and Luxobargewe are all wrong, it's not solid cap and it's not
a rubber that deforms under pressure. I took this cap off a v70
from scrapyard with the idea of dismantling it and cutting it/cutting
it up.

Luckily the cover over this which goes into the tank just came off
easily.





So it is a tiny spring loaded valve on one side for air in, an another
valve for air pressure. And according to a couple of websites and
ebay sellers it is to 22psi (1.5 bar).

As the car is mothers I only get to use it when she uses dads, and
as he is off work for another week. I won't be able to get it to a
garage to do a sniffer test.

This perticual Volvo has done 235,000 miles according to the speedo.
I may not know the innards of an automatic transmission, but I have
had head gaskets go on a Chrysler Neon and a couple of rovers.
So I always keep a regular check on oils and coolants, for the dreaded
mayonnaise or other tell tale signs.

I do realise that the car's cooling system work under pressure, however
it was the lack of a visible means of dealing with this or an increase in
pressure that forced me to post this thread. I have seen what a faulty
pressure cap on a coolant system can cause it to look like a cylinder
head gasket failure.

Luxobarge wrote:And finally I do think you're posting in the wrong forum.
I don't want to raise the age-old argument about what is a classic, but
I think it's fair to say that a 1997 Volvo V70 isn't one - by a very long
shot IMO, that's why I don't post about mine here.

You forget 2+ heads are better than one. And as there are people on here
who if you added the years of knowledge up to well over a couple of
hundred years on here. Plus I didn't just ask on here.