Overheating TDI

[muddyboots]

Since buying the Passat I've covered about 44,000 miles - and during that time, the temperature guage has stuck firmly at 90º (except when warming up from cold, obviously...) regardless of outside temp, driving style, etc etc.

About a week ago, I got a warning on the dash display to "Check coolant level". Sure enough, it had just dropped below minimum in the expansion tank - so I bought some G12 coolant and topped it up.

Couple of days later, I was giving it some serious beans up a hill (Cat'n'Fiddle road, if anyone knows it) - when power went down quite dramatically. Looked at the gauges, coolant temp was almost at full scale, must have been around 120º. Nowhere to pull in so drove very gently - and within 30 seconds max it was back to 90 again, and power was restored. Stopped and checked coolant level - it had gone down a bit.

Since then, the temp stays at a constant 90 all the time, EXCEPT when I give it a prolonged blast at full load. Then it starts rising quickly. Calm down and drive normally, and it's back to 90 very quickly.

Coolant level is now back down to minimum level, so reckon I've lost a litre or so in the last week.

Had cambelt and coolant pump changed earlier this year at 120k miles.

Any ideas ?

In summary:
- Temp only rises during prolonged full load
- Fine during normal driving or when in traffic
- Drops back to 90 very quickly if I ease off
- No abnormal smoke
- Performance normal (except when overheating, guess the ECU cuts power)
- Idles smoothly
- No mayo in oil filler cap

Not liking the sound of it

 

[UncleFester]

Possible coolant leak somewhere or maybe the first signs of a gasket on the way? Might not be a head gasket though - if it was fine before the water pump done, maybe there's a gasket gone there or something has worked loose? Have you parked ot up on nice clean concrete after filling it and had a look to see if there's any marks on the ground?

Water is definitely going somewhere so that rules out just a faulty sensor somewhere.

 

[muddyboots]

I've just sat in the car for at least 5 minutes, holding it at 2500rpm.

It went up from 70 (it had been stood for a while) to 90, and stayed rock solid at 90. So I'm fairly certain it's not a fan problem, or a thermostat problem.

It's only under full load that the problem occurs.
I guess it could be the pump; able to pump sufficient cooling for normal use but not able to supply enough when the engine is working at it's hardest. I really hope it's not as it's a ******* to get to, and could really do without paying several hours labour to my garage.

 

[JonTelfer]

How is the water pump driven? How about this for an idea - if the water pump is driven by a slack belt which is sufficiently grippy to turn the pump at low loads but there isn't enough friction to drive the pump under high loads.

or maybe broken blades in the pump giving it a much reduced capacity?

NB: random thoughts could all be rubbish ideas

Jon

 

[muddyboots]

It's driven by the cambelt - which is toothed so no chance of slippage.

I think the idea of a damaged or slipping impeller is most likely, from reading around it seems a very common fault

Not sure why the coolant level drops though

 

[m0rk]

how's the rad looking? covered in leaves this time of year? rusted?

 

[goble]

headgaskets gone and its getting burnt off in the cylinder.

 

[muddyboots]

I really hope not - I'd rather it was the water pump !

 

[muddyboots]

Mind you I've had heads off and on pretty quick before....just on far simpler engines !

 

[muddyboots]

how's the rad looking? covered in leaves this time of year? rusted?

Had a check to make sure it wasn't blocked by debris, looks it's normal self. Can't see any leaks.

 

[air121005]

the standard water pump used by SEAT and other VAG models have plastic impellor fins!
its not uncommon for these impellor blades to break off,
at normal usage the fewer blades may be able to keep water flow sufficient to maitain constant temperatures, but when you boot it, making the engine work harder / it getting hotter, the reduced flow can't dissapate the extra heat generated.

when you had the water pump changed, do you know if the replacement part had a plastic or metal impellor?

maybe a techie could tell you how to check if the water pump is working efficiently

 

[aceman]

If the coolant is being lost due to the head gasket and coolent getting into combustion chamber I think you can do some kind of chemical check with the coolant which will tell you if it contains traces of combustion materials. I think its just something like strips that change colour when dipped into the expansion tank.

If you only had the pump changed earlier this year it may be covered by warrenty if it is this that has failed.

A mate of mine had exactly the same problem with his Bora 115pd but never got to the bottom of it before he sold the car on but he did rule out the head gasket and radiator and the only conclusion was that it was the pump and decided to get shut due to other problems as well.

 

[muddyboots]

Ian
I did wonder if the garage (local independent) would change the pump under warranty, but it's covered 16,000 miles since they changed it earlier this year - so I doubt it...

 

[muddyboots]

the standard water pump used by SEAT and other VAG models have plastic impellor fins!
its not uncommon for these impellor blades to break off,
at normal usage the fewer blades may be able to keep water flow sufficient to maitain constant temperatures, but when you boot it, making the engine work harder / it getting hotter, the reduced flow can't dissapate the extra heat generated.

when you had the water pump changed, do you know if the replacement part had a plastic or metal impellor?

Hmm, that's the conclusion I'm coming to after googling around.

I don't know what sort of replacement it had, didn't think to check

 

[air121005]

Muddyboots,
have you had your car looked at, any ideas what the problem is?

 

[muddyboots]

Not yet.
But I've read so many stories about water pumps failing and being unable to provide enough cooling under high load, I'm 90% certain it's that.

Going to order a new (metal impeller!) pump, and take the plunge & do it myself. Quite a big job as it means pulling the whole front of the car forward, removing the aircon drivebelt, the alternator/PAS/fan belt, and timing belt.
Even though the timing belt was changed 16k miles ago, I guess there's no harm in sticking another new one on.
Also, when I had the TB done, the engine performance seemed to change and I swear my MPG dropped, so I've always wondered if they didn't adjust it properly (there is some adjustment on the camshaft sprocket - if not done properly it could throw the cam timing out slightly).
Gonna get the bits and do it next weekend I think.

Car runs fine, at a steady 90º unless I really push it hard, so I'll just have to resist any temptations for the next week.

 

[UncleFester]

It's a shame it's the RR day next weekend otherwisei i'd have liked to see you do that - do you think you could be bothered to take photos step by step as you go as well as bits of any mullered parts if there are any?

 

[air121005]

Not yet.
But I've read so many stories about water pumps failing and being unable to provide enough cooling under high load, I'm 90% certain it's that.

Going to order a new (metal impeller!) pump, and take the plunge & do it myself. Quite a big job as it means pulling the whole front of the car forward, removing the aircon drivebelt, the alternator/PAS/fan belt, and timing belt.
Even though the timing belt was changed 16k miles ago, I guess there's no harm in sticking another new one on.

me & a mate changed the cambelt & waterpump on my PD130 a few weeks ago, took about 3 hours (with the odd tea break)
we had to also remove the boost pipes, top engine mount and to get that off we needed to remove the water expansion tank which is fixed on by the vacuum servo bracket

Also, when I had the TB done, the engine performance seemed to change and I swear my MPG dropped, so I've always wondered if they didn't adjust it properly (there is some adjustment on the camshaft sprocket - if not done properly it could throw the cam timing out slightly).

i'd be very reluctant to adjust the camshaft sprocket unless you really know what your doing
you have only to get it wrong by a fraction of a degree and it will run badly if at all or even worse a clash of engine parts.

Gonna get the bits and do it next weekend I think.

i found SEAT to be cheaper for the cambelt and my local motor factors type place cheaper for the water pump (with the metal impellor) and tensioner pulley

 

[air121005]

did you change the water pump, has it cured the problem?

 

[muddyboots]

Haven't done it yet !
Planning to this weekend. I have the pump, still waiting on the cam/crank locking tools. Need to buy the cambelt & drivebelt too.