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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21596
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a daf cf 85 tipper truck I had to change the

Customer Question

Hi, I have a daf cf 85 tipper truck I had to change the termostat due to it being faulty not working. Since fitting the new one the truck has ran hoter than it did before.before changing it the temp gauge usally ran just over quarter and when engine came under a pull it would go up to half. At moment in runs at half which seems pretty normal and when comes under pressure it rises to 3quaters on the gauge? It never goes any further and always returned to half fairly quick.the problem now is that it keep throwing out a little water from the header tank through the over flow pipe on header tank it can be visable on the grill of the front off truck. It only goes to a certain level and then not near as much and yes I don't have the header tank to full it's filled to correct level. It always sets of the coolant warning light in dash. Prob uses between half litre to a litre some days depending on the job. I have changed radioator cap and changed the radioater just to rule out these. My mechanic wants to do the head gasket but I'm very slow to go down that route as this prob started 7 months ago and hasn't got worse so I think that's not the problem. Maybe I'm way out but would it be possible the new thermostat is letting the engine run a lot hotter than the old one hence the problem??? Would be for greatful for any advice or solutations. Cheers lads
Submitted: 9 months ago.
Category: UK Car
Expert:  Matt replied 9 months ago.


1st to ask is the new thermostat the same specification as the old one?

as they do come in a few opening temperatures, if you look on the body of the thermostat there will usually be a number stamped on it like '78' or '82' this is the opening temperature in centrigrade

I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly.

So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked

If these are OK then remove the tank pressure cap and run the engine from cold with the heater set to full hot

As the engine starts to warm, squeeze the large hoses running to the radiator to help displace any air - all the time keeping an eye on the level in the header tank, making sure it doesn't drop below the minimum and open any bleed screws built into the top cooling hoses - closing them off as soon as they start to gush water

Once the engine is up to temperature the tank should be quite full. Switch the engine off and leave it to cool

Then top up to the mark once its all cold and replace the cap

If all of this is OK it may be worth replacing the header tank cap as again you can lose coolant as steam if this is blowing off too early ( the cap should hold pressure of around 1Bar)

if its still got an issue after this and its still spitting water out then I'd agree its wise to test for head gasket

The other thing to try is a head gasket / block test kit as these take a coolant sample and analyse it for any signs of combustion gas - if present this would indicate the head gasket is on its way out

Expert:  Matt replied 8 months ago.


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