VW 1.9 tdi overheating advice

[Gadgeroonie]

mk 4 golf TDI

car runs fine but it seems to overheat on motorway

the heater in the car goes cold and then the car overheats

if you rev car to say 3000 rpm the car cools down again and the heater goes hot again

the pipe to the thermostat is cold

I have tried

new water pump
new thermostat
real steel - to fix a faulty headgasket


the water in the car is muddy brown

i have had a sniff test done on the headgasket and it came back clear

Anyone had a similar problem ?

[cuprabob]

These cars are notorious for radiator fan problems but that would be more of a problem in traffic.

[Gadgeroonie]

the fan does appear to be coming on ok

by driving the car in a lower gear ie keeping the revs up the car seems ok

[shtu]

Sounds to me like you have ancient coolant, a sludged-up block and rad, and people have slopped many, many bottles of goop into it to bodge up a leak somewhere.

I would,

1) Flush the cooling system, using a chemical cleaner.

2) Flush the block, radiator and heater using a hose to force water through the system.

3) Change the coolant for fresh.

4) Deal with the inevitable leaks, without using goop.


edit - It doesn't sound like an airlock, and they don't seem prone to it. It sounds like a blockage to me. "muddy brown" coolant sounds like someone has added the wrong kind of coolant at some time - it should be bright red, there are specific types for use in VWs available from parts factors.

Edited by shtu on Tuesday 11th December 13:09

[coetzeeh]

^^ this

[Gadgeroonie]

it did at some stage in the past have some of that stuff put in it to cure a leak

it has had a chemical cleaner added
flushed out under pressure
new water/fluid added

still has the problem

[mk1fan]

Has the water pump ever been changed?

VAG pumps have (or did have) plastic impelas which disintergrate over time. Common 'fix' to swap out the plastic VAG unit for an aftermarket brass item (GSF & Eurocarparts do them) when the timing belts were changed on petrol models.

ETA - sorry missed the bit in the OP.

It might be the temp sender unit but this wouldn't account for the cold pipe and they usually read cold if they fail.

How much fluid was put in the system when it was changed? Not sure how much the dervs need but it's about 4.5 litres on the petrol 4-pots.

Edited by mk1fan on Wednesday 12th December 12:33

[shtu]

Gadgeroonie said:

it did at some stage in the past have some of that stuff put in it to cure a leak

it has had a chemical cleaner added
flushed out under pressure
new water/fluid added

still has the problem

I don't believe it's been done properly. If the coolant was new it would be bright red, and not the muddy brown you describe.

Get it done properly, and half-expect to need a new radiator - I suspect it's at least partially blocked with all the rubbish that's been added.

edit - unless you're saying it was done yesterday afternoon, in which case I would suspect the cleaner hasn't been left in long enough to have any effect, or that the rad is so blocked it won't work.

[Cloggie]

99% sure the plastic impeller on the water pump will have separated from its shaft.

[shtu]

Cloggie said:

99% sure the plastic impeller on the water pump will have separated from its shaft.

Unlikely to be that,

- He says it's had a new pump.
- He says the temperature drops back to normal at higher engine revs, the opoosite of what you get with a failed pump.

[Gadgeroonie]

hi guys

thanks for the suggestions

the car has had a new water pump and rad approx 6 months ago

does sound like it it blocked up somewhere

somebody did tell me filling it with harpic might do the trick !

[mk1fan]

shtu said:

Unlikely to be that,

- He says it's had a new pump.
- He says the temperature drops back to normal at higher engine revs, the opoosite of what you get with a failed pump.

It could be that part of the impella is broken and the extra revs compensate. At this stage though, I would look for a blockage first.

[Cloggie]

shtu said:

Unlikely to be that,

- He says it's had a new pump.
- He says the temperature drops back to normal at higher engine revs, the opoosite of what you get with a failed pump.

Sorry, I'll learn to read first.

[shtu]

Gadgeroonie said:

somebody did tell me filling it with harpic might do the trick !

No! It's had enough rubbish poured through it already.

The cooling system on these is pretty damn simple - start dismantling and flushing each part in turn, ie, take the coolant hoses OFF and flush them, check for any internal damage, etc. Could be a bit of hose has peeled off internally and acting like a flap valve...

Take the 'stat out before flushing the block, and do every part in both directions.

[renorti]

i used to break a lot of mk4 golf's, heard a few people with same trouble of their cars overheating only on the motorway.
headgasket starting to fail, so look in that direction.
check for pressure in the expansion take, look for bubbling after a good run, sure signs.

[Gadgeroonie]

no more pressure in the header tank than you would expect from a normal warm engine

when the car overheats water comes out the top of the reservoir bottle

[4key]

I know this is going to sound a bit stupid, but most of the practical stuff seems to have been mentioned.

Try a different cap on the expansion bottle, ive had a couple of vag ones that wouldnt hold much pressure and just sprayed water out.

[Gadgeroonie]

Hi, I did actually fit a new cap back at the start

thanks for the suggestions

[shtu]

Final thought, you mention you had a sniff test done, try getting a pressure test done on the system too. If the HG is failing it should show up there.

[Gadgeroonie]

good idea - i will get it pressurised