Slight overheating and coolant loss

[Chickenhawk]

My A4 1.8T Sport ('98) with 75k on the clock is beginning to run a bit hotter than it should - normally sits at 90 degrees all the time, but has started to run hotter when cruising on the motorway (gets up to 100 - 110). I put the heater on full blast and it drops down to 90 again, stays there a bit then creeps back up again. I have to top up the coolant level about once a week now - uses about half a litre a week, though it's not consistent.

I've blown out the rad to clean it, it's had a new cam belt, water pump and oil pump this year (had brown mayo in coolant about six months ago - new oil pump sorted that). Not getting any water in the oil and not using any more oil than usual. Any ideas what I should check?

Is the head gasket on it's way out? Thermostat knackered?

Apart from that it runs fine....

[Audi A4 Lover]

Its probably just a normal water leak i.e a leaky hose somewere.Best thing to do is pressure test it and just look for the leak, if you cant presure test it, just let it run up to temperature and see if any drip marks appear on the floor then use those to guide you to the problem. If your confident that its not just a leak, then you can start looking at more serious problems, i.e headgasket, heater matrix etc.

[viodiesel]

Overheating may cause a slight coolant loss through vaporization.
Cooling through heater shows satisfactory operation of cooling pump and reduced cooling capacity of radiator which might be caused by reduced coolant flow through it-so I would say the problem is the thermostat. Since water pump was changed small remnants may stick btw valve/seat of thermostat, thus preventing proper closing of cooler by-pass duct.
Blown head gasket will normally lead to pressurized gas ingress in cooling system and you should see some vapour blow from expansion vessel vent
If you want to check the thermostat yourself make sure engine is not hot and slowly remove the expansion vessel cap to release eventually trapped pressure
Good luck

[Chickenhawk]

Thanks for all this advice - much appreciated. I'll let you know the outcome...

[Chickenhawk]

Hi,

Back again - bit of a weird one this as my local garage can't work it out either. It's been in 3 times (and beginning to cost a bit) - had the thermostat and aux fan switch changed, flushed the rad - and it's still heating up, and the secondary fan is still not coming on either...

The rad is cool at the bottom (where the thermostat is), yet it's boiling hot at the top. Water seems to be flowing through the system, though I'm not sure if it's fast enough. When I carefully take the cap off when it's warm / hot, it boils up and erupts out the top of the tank like a volcano, then drops back down again so the tank appears empty (like it's got air / gas / pressure in the system - don't know if this is right?) then boils up & erupts again. Secondary fan still not coming on, and had new water pump and oil cooler less that 6 months ago. Both oil and water temp gets up to right temp and stay there, and then after 20 - 30 mins starts to overheat from then on - oil temp is running about 115 - 120, as is water temp.- and second fan still doesn't come on (though it & it's relay have been tested and works fine). Still cools down fine to right temp if I blast the heater on full for a while, then if I turn heater off, it creeps back up again. Got no water in the oil, so hope it's not head gasket...

I'm a bit lost as to what to do next - and so are the guys at the garage. Thinking of taking it to Audi, but will have to sell a kidney to pay the bill if that's the case...

Is it a partially blocked up rad / do I have to replace it? Water pump failed already & not mixing / pumping it round the system enough? Oil cooler failed already? Blocked coolant pipes? Anyone had similar persistent problems?

Any additional advice would be gratefully received as it's driving me mad (and into the poor-house!)
https://www.vwaudiforum.co.uk/forum/i...ies/aargh4.gif
Many thanks!

My A4 1.8T Sport ('98) with 75k on the clock is beginning to run a bit hotter than it should - normally sits at 90 degrees all the time, but has started to run hotter when cruising on the motorway (gets up to 100 - 110). I put the heater on full blast and it drops down to 90 again, stays there a bit then creeps back up again. I have to top up the coolant level about once a week now - uses about half a litre a week, though it's not consistent.

I've blown out the rad to clean it, it's had a new cam belt, water pump and oil pump this year (had brown mayo in coolant about six months ago - new oil pump sorted that). Not getting any water in the oil and not using any more oil than usual. Any ideas what I should check?

Is the head gasket on it's way out? Thermostat knackered?

Apart from that it runs fine....

[kite]

Just a thought, Your 2nd fan is not cutting in but using the heater drops the temp, I would investigate the 2nd fan problem, if you can get that working it would have the same effact as using the heater. does the 2nd fan get switched by the coolant temp. sensor, could that be the problem, coolant sensors are known to fail.
Hope that makes sense

[mbu10]

just a idea
and have seen something very similar on another car which would lose water all the time with nothin in oil (water)and nothing in water (oil) and
heated up and not cool properly

well what is it the water in your cooling system is meant to be under presure
just slightly which raises the boling point etc etc (think some where between 1-2 bar if i remember rightly)

anyway in the car i had with this kinda problem
it was the screw top the one on the expanstion tank
this has pressure release valve as well (to stop car cooling going pop)
it was leaking air which stopped it gettin to pressure
which then started to get close to boil point 90-100 deg
which then stopped it cooling correctly
got hotter
leaked water from faulty expanstion top
etc etc

now this is just a idea as i have seen on a car i owned before
sorry spell check not working and my spelling is so bad
just thought would give my 2 pence worth

[Chickenhawk]

Thanks for these replies - much appreciated - gives me some other options! (temp sensor was changed about 6 months ago - but could be faulty again)...

Will let you know what happens...

[Col]

If the water pump has never been replaced and given the age, could be. (not read everything above, you may have mentioned it)

The impeller de-bonds and slips on the shaft which effectively leaves you a pump that does not pump. Very common problem.

[Chickenhawk]

Many months later - I should have replied to this thread back in April when I started the post but I forgot - soz - so here goes - might help someone else with coolant problems...

Eventually got to the root of this problem - having gone through everything. Checked all sensors & switches, thermostats, waterpump had been replaced not long ago, flushed rad, had right coolant in it, checked coolent pipes, heater matrix, checked expansion tank cap valve, second cooling fan - so last thing was the rad - and after put in a new one, it worked fine and temp stays rock steady at 90 - even in summer and on long journeys.

What we deduced was that the year before, it had oil cooler probs - and got that gunky brown oily mayo stuff in the coolant system when it leaks in a bit of oil with the coolant - nasty. New oil cooler and that solved the sludge forming.

Problem was that the some of the sludge had got into the rad, and even though it was flushed, it was not done properly, and so over the following year, the stuff had shifted around the system and collected in and clogged up parts of the rad so could not cool properly, and was not getting to the thermostat, so started heating up and cooked solid so would not shift even after flushing.

In summary - if you ever get that gunky brown sludge in the coolant system from a failed oil cooler, make sure the rad (and rest of the system) is properly flushed out untill you know that it's a clean as a whistle. Would have saved me a lot of time, stress and cash!