Volvo V40 GDI overheating - mystery cause.

As you have replaced the rad with a very good quality nissen, I would say you still have a partial airlock, based on that you say the top hoses are not full of coolant- they should be.

I would try bleeding it with the engine at a fast tickover, some gloves, rad cap off, and partially removing hoses to hopefully expell any trapped air.

I often find parking with the nose uphill as steep as possible helps with troublesome cars (french normally!) whilst re-bleeding...

Tim..

blocked radiator

snipped-for-privacy@mail.com formulated the question :

Airlock, obstruction somewhere - collapsing hose, stat not opening fully perhaps, obstructed engine water channels, pump impeller partially corroded away and not providing a full flow through the system.

As it warms up from cold.... your gauge should rise to a level, perhaps fall back a bit as the stat opens, rise up again and settle - after which it should stay perfectly still unless there is some sort of problem.

You won't see this sort of indication on any reasonably modern car. The output from the ECU that drives the gauge is conditioned to effectively be a three-state indicator - Cold-Normal-Hot. You would get as much information from two led's; one "engine cold" and another "engine overheating"!

This was done because cars run with a much wider range of temperatures quite acceptably now. Dealers were getting lots of customer complaints that their new car was overheating, although it was actually within allowable limits.

Chris

Thanks for that. The rad itself does not have a cap, but a hose to an expansion/filling tank with a plastic cap in the corner of the engine compartment. The expansion tank has markings showing MAX and MIN levels for the coolant, and the level is between those, and the tank is higher than any other component of the engine. The manual does give the coolant capacity of the car, and I would somehow have expected the garage to have put in the requisite amount when the rad was replaced (twice). Perhaps my expectations are too high.

The owner's manual says nothing about how to cure airlocks :-(. I wouldn't know which hoses to loosen. I have visions of dumping all the coolant on the ground, which, while amusing for more technical bods, wouldn't help me a lot!

Sid.

Thanks for the suggestion. While not impossible, it seems unlikely to me,as the radiator is less than a year old. I'm no expert, though - how might it be blocked? What would have caused it, and how can I diagnose that in a cheap and simple (remember, I'm a mechanical numpty) as the cause in preference to the other possibilities mentioned elsewhere in this thread?

Thanks,

Sid

the last time I came across this was on a granada, symptoms like yours, fine till a bit of extra effort needed, then it would overheat. I found that I could feel cold areas on the rad, while others were hot, a new rad fixed it. A friend had a very similar fault on a diesel sierra, he already had a new rad and was a bit stumped, the hand test found that only one end of the rad was hot, in his case an internal baffle had broken and instead of the water crossing the rad and coming back, the water just went in the top pipe and fell straight down to the bottom pipe. Another problem that is now more common is having an aircon rad in front of the main rad, it blocks very easily and restricts the air flow a lot. Have you had a test done for a blowing head gasket? again it can cause your symptoms

Thanks for the suggestions - are there any cheap and simple ways to distinguish between the above possible causes? Or possibly work I can direct a garage to do (a) in the order of most probable to least probable or maybe (b) cheapest to most expensive? E.g. is it possible for me or the garage to easily visually inspect the impeller, measure flow rates/volumes at key points etc.

I didn't mention that nothing shows up in the ECU log. The garage looked. They have replaced the coolant temperature sensor on the grounds that it may actually have been misreporting. It wasn't, unless the new one has immediately failed in exactly the same way as the old. In their experience with the marque, it was a known failure mode for the sensors to misreport, hence the swap out. Unfortunately, in my case, this didn't solve the problem.

That's pretty much what it does. From cold, it warms up - after a short period from engine switch on, the heater works (I assume a thermostatically controlled valve is opening to allow hot coolant through to the heater matrix) and the temperature keeps rising until it is stable with the indicator (conveniently, probably by design) horizontal. It stays horizontal indefinitely until going uphill for long distances at high speed - say 4-5 miles at 70 mph at a fairly low gradient, then starts rising slowly - this can be 30-40 minutes after switch on. If I run out of hill, the temperature does go down to the horizontal indication on it's own. Longer hills require me to either slow down or set the heater on full blast (or both), to keep the indicator out of the red.

Is it possible there are two thermostatic valves - one to the heater matrix and one to the radiator? If so, it is possible the one to the radiator is not opening fully (it does open to some extent, as the radiator hoses get warm).

Regards,

Sid

I'm not sure what you mean by reasonably modern? Less than 10 -years old, perhaps? In any case, the coolant temperature indicator on my V40 GDI is definitely not tri-state. It gradually drifts up when driving uphill at speed. If it steps, the steps are too small for me to distinguish. While I'm happy if it is normal for the coolant temperature to vary, I'm not happy to let it go into the red as an experiment - and once climbing, the rate of climb is enough to convince me it will not stop unless I do something.

Cheers,

Sid

Thank-you! Feeling the rad is cheap and simple (just so long as I don't lose fingers to the fans). I'll have an opportunity after a long run this afternoon. And you've gently pointed out I should/may have two rads - engine + aircon (I'll go and count them).

I may also use a digital food thermometer to check the hose temperatures. The owners manual for this engine variant (B4184SM/SJ) says the thermostat starts opening at 82 degrees centigrade (and just for fun, that the system runs at 75-105 kPa), so the temperature of the hose to the radiator should be at or about that. If it is significantly different, it gives me more data. The manual also says there should be 6 litres of coolant - the garage are unlikely to have recorded how much went in last time the coolant was changed, but if I get them to do it again, I'll make very sure they record it.

Thanks again.

Sid

snip

The fan may not be coming on the thermo switch is a common problem, Check whether the fan is working, leave it idlling for a while and watch the temp guage, if it climbs above where it normally sits the fan should come on, or when it gets hot when driving check the fan is actually running

Des

I'll check again. When this happened on the A21 Northbound, I pulled into a convenient lay-by and opened the bonnet. Both fans were working. Back at home, after 70+ miles of motorway driving, leaving it on idle, from memory one fan ran intermittently and the coolant temperature reading was stable within the limits of my eyesight and the markings on the gauge. No harm in checking again.

Cheers,

Sid

The fan is irrelevant when the car is moving above walking pace- if the car is overheating at motorway speeds uphill you could have as many fans as you like and it would not make the blindest bit of difference...

tim.

Only one thermostat.

I would say either you have low coolant flow due to an airlock (most probable) or partially stuck 'stat, or restricted radiator -new, but still possible- check with a hose pipe- should run out the bottom as fast as you can pour in the top- obviously requires draining the coolant.

I would discount a faulty pump as it would rapidly overheat very quickly, and the heater / rad would be stone cold.

When did you notice this problem occuring- was it before or after the head gasket??

Tim.

Thats odd .. on a number of diesels I have had, when on a long uphill drag at speed, the fans do come on, and on a bx 1.9td when the fan switch failed it gave the exact symptoms described, fine at 50/60mph but as soon as I made it work on the motorway the temp used to climb. a replacement fan switch sorted that! I agree you would have thought a motorway speeds the airflow would have been enough but the fans must direct/suck the air a bit more efficiently

Though as also discussed a partly blocked radiator or build up of dirt between the aircon and rad would also give those symptoms, and don't forget the intercooler may be in front of them all! and that may not have been looked at when the radiator was replaced.

Des

Des

Granted about the a/c condensor, but no intercooler- this is a GDi, i.e. petrol!

Tim..

snipped-for-privacy@mail.com laid this down on his screen :

It seems to be pointing towards an inadequate flow and your no cost first step is to make sure there are no airlocks in the system. Usual method is to park it on a steep up hill slope with engine cool/cold and filler cap off. Start it up and watch for air being expelled as you keep topping it up. Obviously never remove the cap with the engine hot, as it can boil up in your face.

No there is only one. From cold... Water (coolant) is pumped around the engine and the heater matrix only, until the thermostat opens which allows it to then also pass through to the radiator. The thermostat then works continuously opening a bit more, closing a little to maintain a stable temperature in the engine - which was why I suggested it may not be able to open fully, which would thus restrict the amount of heat the radiator could dispose of.

Another possibility occurs to me that the radiator might be one for the wrong model of car, but still fit. Could you do any checking? I'm not suggesting is definitely possible, I just don't know the Volvo models. Just another check to be added to the list of possibilities.

I knew that.......

actually petrol turbos have intercoolers as well, but I forgot it was the Mitsibushi GDi engine. why can't they only use D for diesel engines.........

Des

Something for the garage to check...

Thanks - useful to know.

Long time after. Approx 12-18 months.

Cheers,

Sid