Overheating 850 T5
 

Hi folks,

New to this forum, and not actually the owner myself, but posting on behalf of my brother-in-law who owns the T5 in question.

Its a 1990 850 T5, and he's been having lots of problems with it overheating recently - there was no gradual worsening of the condition, it was fine one day and stuffed the next. We checked the thermostat and found that to be sticking shut occasionally, but weren't convinced that was the only fault, so temporarily rigged it open and ran the engine again - it still overheated even with the thermostat jammed open. We then thought it might be the water pump, so we stripped that off but found it to be in good condition, the bearing nice and smooth and the vanes all intact.

We then flushed the coolant system out several times, and used cleaning additives from Halfords too. Got a fair amount of muck out, but it was running clear by the end. Still no joy, still overheating. A local garage then suggested it sounded like the cylinder head gasket due to some of the symptoms we described, so we stripped the engine down and replaced that, though in fairness it looked to be in pretty good condition when we removed the old one. Engine re-assembled, everything reconnected and still overheating.

We then decided it might be the radiator, so got a replacement and fitted it, flushed the system again...and still overheating.

Is there something simple we're missing here? Can anyone else think of something it might be? All the hoses seem to be in good condition and unblocked, its just something in the system thats not letting the hot water through to be cooled properly. After a minute or two of running, the water is boiling at the top (around the filler tank) and runs out luke warm at best at the bottom of the radiator.

All suggestions gratefully received!

Rich

Are you getting any error codes from the ECU?

could it be a faulty coolant temp sensor?

and is the main fan kicking in?

I've experienced both of those problems!

If its the CTS it'll light the CEL, the fan not functioning will just log an error code without lighting the CEL.

Hi,

I'm not sure about error codes or warning lights, I'll ask him about that. I dont recall any but then my head has usually been under the bonnet, not in the car.

The main mystery is that the hot water doesnt even seem to be reaching the radiator properly, almost as if its being bypassed somehow. The expansion tank and top hose get boiling hot, but the radiator itself barely gets warm. I had assumed that by jamming the thermostat 'open' it would force the coolant to circulate throughout the whole system, ie radiator included - is there some other shut-off valve that is controlled by the coolant temperature sensor that might have this effect or something? The fans seem to work ok, as far as I can tell, but as the radiator never really gets hot, they dont seem to trigger very often.

I appreciate the suggestions so far, any more thoughts?

Cheers,

Rich

I took my t5 to a volvo specialist who told me that the car was NOT overheating despite the fact that it clearly was and thast it was simply a gauge fault. The advice was replace the gauge with a second hand unit. Three months later and still driving fine.

Heh, wish it was as simple as that, but sadly not!

The water is literally boiling, and blasts back out of the header tank if the cap is unscrewed. I'm pretty sure thats not healthy ;)

Rich

hmmm, bizzare mate.
from what youve said, it seems like there could only be a couple of probs which would prevent the coolant flowing.

water pump not pumping: is there flow back to the header tank ?

a blockage: what did the coolant galleries look like when the head was removed ? a coolant pipe folding on itself under pressure ?

to start with , id remove the thermostat, fill it with cold water and remove the return hose (hot coolant into radiator hose) point it away from myself and anything electrical and turn engine over to establish wether or not the coolant is indeed being pumped.

if flowing, id make 100% sure there wasnt any air locks and change the temp sensor.

if not, id look at all hoses to be sure theres no kinks or blockages .
you say its had a new rad and the pump itself was fine ,so if none of the above are impeding flow..... id start scratching my head. lol

wayne

One obvious thing that's not been mentioned - Filler cap. New (good) ones are green, old ones are grey.

Whilst this won't stop the water circulating in itself, if you run the system at low pressure you get localised boiling very quickly and cavitation in the water pump. Also in my experience, it can be difficult to get rid of airlocks in the system which will also cause boiling.

im with him ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cheers
jod