Pressure in radiator hoses
 

Hey Peeps,

I'm trying to diagnose an issue with building pressure in the top and bottom radiator hoses. It feels like there's more than would be expected.

If I run the engine while parked, the temp builds up as expected and the hoses stay pretty malleable but for a while the hoses have had almost zero squish in them after a short drive.

I've put a sniffer on the expansion tank which came up fine and there's no sign of anything suspicious and the oil in the head and sump (it's black and not like custard)

I used a bottle of wynns flush and then a bottle of leak stop just in case and it's got a fresh batch blue Ethylene Glycol coolant and there seems to be more squidge in the hoses but that could just be me hoping something's different.

It runs and drives absolutely fine.

I've ordered a inline T adapter for a Stack mechanical temp guage which I'm going to use to see what temp the coolant is getting to as I know the volvo one in the cluster isn't really helpful on that front but is there anything else I can look at to find out why this might be happening?

Cheers.

It is supposed to pressurise to keep the coolant from boiling it will raise the boiling point up to about 120C at 1 bar pressure ( 15 psi ) The release pressure is marked on the cap. The cap controls what the pressure is in the system... I assume you have the correct VOLVO Pressure cap?

In my experience, these hoses are preety soft and squeashy, at least when hot. But I guess the concept of pressure in this case is subjective. Also I imagine that the quility of the hose, if they are oem or not might also change the feel. Honestly sometimes when I squeaze one of this, I have the feeling that is empty, so I guess it never really felt very pressurized to me.

I am not sure if crankcase pressure can be felt in the expansion tank/coolant hoses without head gasket failure. Logic tells me it couldn't, but then again I am not a mechanic and so I would test the crank pressure. Have you tried the glove/platic/paper test on the oil intake of the engine to see if the engine is blowing up air? It wouldn't hurt to try. Have you cleaned the PCV box recently?

I have never felt that the rpessure was enough to make the hoses feel bloated or rigid though, especially when the rubber is hot.

In cool or moderate British weather I have found the pressure unremarkable in a properly working 900 series cooling system. You should be able to squeeze the large radiator hoses by at least 1/3.

Thoughts about what might cause higher pressure:

• HG failure. Maybe only a very small leak.
• Turbo leaking into cooling system or overheating coolant if water-cooled.
• Faulty or incorrect pressure cap.
• Faulty or incorrect thermostat.
• Incorrect coolant/water mix.

You could try a lower pressure cap (e.g. black) but this isn’t a great solution if you’ve got a genuine fault somewhere.

Is your car a manual or an automatic, 'Casheye'? If it is an automatic, another possible cause may be failure of the ATF cooler integral with the radiator. This, which allows cross contamination of the coolant with the ATF, happened on my 745 with similar results. This was also accompanied by other symptoms, notably 'mayonnaise' in the expansion tank.

In the absence of any other symptoms it is unlikely to be the problem, but if it is it needs urgent attention to avoid terminal damage to the transmission. I was lucky in catching mine early. Just needed to flush the cooling system and the tranny, and replace all of the hoses* with no permanent damage, but many are not.

Regards, John.

* Edit: Hoses, not holes! Bloomin' predictive text! J

There is only one thing which will cause genuinely higher than standard pressure in the cooling system , that is the cap.Its set to blow off at lets say 1.5 Bar for now.( There are various pressures for different years and engines.) So if the hose feels very hard then its likely the cap is not working.or the wrong cap ( or it could be working !) 1.5 bar will give a fairly hard hose , if it is soft the cap is probably leaking.

It would be a good idea to put a pressure gauge in the bleed line going to the coolant bottle. That will define what the vague "Hard" and " Soft" mean.

So worst case if the head gasket is leaking, the excess gas/coolant will be blowing out the cap vents , you can't miss that really.

Yes It is pretty Obvious if the transmission cooler is leaking, it tends to be a very small leak rather that all gushing out. I have had this problem about 5 times in my long career fixing these things so its not at all common and you see the white mess in the coolant bottle easily. It is Important to change EVERY rubber coolant hose on the car if this happens as the oil gets into the rubber and over time softens and WILL burst eventually if neglected. I have seen the hoses burst some years later on cars which have declined to have the repairs done and taken the car away for someone else to " Repair" !

This is a very time consuming job trying to flush out the cooling system with an emulsifier and change ALL the hoses even those inside the car for the heater, also very expensive , the last one I did was about 14 years ago and back then It was about £500 for all the hoses and about 4 hours labour .
I don't think this car has that problem though If there is actually a problem at all of course...

I posted this tip before but it could be useful again:~

Flushing the engine & radiator system with standard shop purchased radiator flush is a bit hit & miss.
Central heating descaler is a good option that will not affect mixed metals within the system, many brands available - economy wise it goes a long way.

Used it many times on classic cars a lot older than present Volvo's- follow the instructions on the pack regarding the mix ratio but I generally bring the system up to temperature a couple of time and leave it to pickle as long as you can.
Follow through with a good clean water flush followed by you favourite/correct antifreeze.
Hope it helps.
Bob.

Coolant cap is a green 22psi one and the thermostat was changed not so long ago ( can't remember which one i used... maybe the 87c one )

I took the car out for a drive today. I let it get up to temp while it was parked and the hoses had plenty of squish in them. Took it for a short rag down the bypass and back again. It's an auto and I kept my foot down making use of all the rpms in each gear :regular_smile:

Parked it up and checked and the hoses were much. much harder to squish. I grabbed a temp gauge and took the expansion cap off (slowly) and dropped it in. The reading didn't go higher than 80c.

Coolant mix is about 30/70 coolant to water. It does seem to be dropping ever so slightly but the expansion tank is pretty grubby so it's difficult to be sure on this.

It's an Auto but this definitely hasn't happened. Had this issue before on a different volvo where the transmission fluid turned to custard

The only pressure gauge I've got to hand is one for testing mains water pressure (3/8 bsp i think) for washing machines and the like. I could order a spare cap and drill a hole in it and fit a valve to it.... Doesn't seem like a bad thing to have actually.