Coolant temp problem

[bentaw]

every so often i am sat in traffic and my coolant temp rises ever so slowly then when i put my air con on or the heater it comes down to normal 90 degrees. It doesnt happen all the time which i think rules out the water pump but recently it has started happening more often what could it be

 

[Feel]

Sounds like the fans/fan controller to me. The fans are two stage, the lower speed setting comes on normally, but I understand when you have the aircon on (at least one of) the fans run continuously.

It can be serious because if the low speed cycle packs up, which is a common fault on the MK4 platform, the high speed fans keep coming on and off which eventually knackers the fan motor, which ca then lead to overheating.

Do a search for "air raid"

 

[honeyman]

Have you checked the fuse thats what mine was.

 

[bentaw]

cheers guys will have a look tomorrow

 

[Fruit And VAG]

It could be a slipping impellar... a big problem on VAG cars, or any german car for that matter.

Once it starts slipping it will get worse until it no longer works and your car will rapidly overheat.

If it is your impeller, you will have at most a couple of months before your water pump needs replacing...

However.... you dont state how old your car is and I would expect some serious mileage of 50k+ before this is likely.

If it appears one of your fans is faulty, it could really be one of the sensors as the fans are more reliable as they are just an electric motor in essence (but it depends on who you speak to since many garages will tell you its a fan and put one in with a new sensor to make a bit more cash).

 

[bentaw]

its an 03 plate and has done 47000 miles

 

[Pabs]

Ben mate, my car is doing it recently too!

Worries me.

However, I've ruled out waterpump etc as I had a 60k service done recently, and i have a metal impellar waterpump installed.

I recon its FMIC..... and hot weather. Might talk to forge about it.

It deffo drops right back to 90, but only rises above 90 when stuck in traffic for about 10mins+

 

[Pabs]

please let me know if u get an answer to this!

 

[bentaw]

will do mate i was thinking it could be fmic and the weather but also i cant hear the fan kick in the slow one not until i put the air con on and then the big one kicks in so it might be the fan although if it was the fan it would do it all the time surely

 

[bentaw]

does your temp rise quickly when it goes over 90 degrees or is it more of a steady gradual climb which is what mine is, i think if it rises quickly then it will be the water pump but a more slower climb in temp could be the fmic

 

[Pabs]

Its a very slow climb mate - I see it climb for about 4-5mins i recon, then it hits about 100 degrees (not quite 3/4 the way around) and then drops quite quickly afterwards. If I'm in traffic for say 10mins, it does it about 2 times during this period.

 

[Pabs]

Also, i'd think waterpump if it did it all the time, but it doesnt do it when idling - only when in traffic.

I'd assume heat from other engines, + load on engine while driving from 0-5mph-stop-5mph etc would make engine work harder than just an idle.

Coolant level is fine, thermostat has also been changed.

next bet is coolant temp sensor.... but not sure?!

 

[bentaw]

mine does it also at idle but not all the time i can sit there at idle for about 20 min then it starts to do it so i am guessing mine is down to the fan not kicking in. But it also does it in traffic more often i also thought thermostat but if you have replaced yours and it is still doing it then i dont know what mine is

 

[Pabs]

i think i'm going to point the finger at fan controller next. I'm also going to post in Forge forum and see if they've come across this before, they might be able to help.

Don't know what else to suggest at the moment.

 

[Fruit And VAG]

If the fans are working, then either a sensor faulty and not kicking in the fans at the appropriate times or the impeller is slipping. I suspect the latter if you have have a heavy right foot... and who on this site drives like Miss Daisy

On a VAG car there really isnt much you can do for weird coolant temp problems except get it to a gargage for a poke around.

 

[JohnL]

If its the fans, your temp will be fine until the high speed fan fuse blows. Then you'll have no fans and a very hot engine.

It's very easy to check your slow speed fans. Just pop the air con on and have a look and see if the fans are spinning. If they are constantly spining at slow speed they're ok. If they keep stopping and then coming on again for 10 seconds of so on high speed, then they're broken. If they're broken then the slow speed resistor has gone, which is an integral part of the fans, and you'll need new fans. (I just had mine replaced on tuesday, 03 plate car with 20k).

TBH this doesn't sound like that fan problem, although it could be another fan related problem.

 

[Pabs]

certainly not a fan problem on mine. Fans work fine.

 

[Fruit And VAG]

certainly not a fan problem on mine. Fans work fine.

There is a small chance your thermostat is sticking at low speeds. If your fans kick in at the right time and for the right duration at other times, then you should assume all the associated sensors involved in the coolant system are also fine. This still leaves the impeller as possibly slipping and on its way out. However, this thread has been running a while and if it was that then I would have expected your temp problem to get more severe quite quickly. A thermostat is cheap and easy to replace.

One other possibility is that you have some solid particulate grundge floating about your coolant system which collects together to form partial blockages at low speeds. I cannot see why you would have this on a such a new car with its mileage unless you bought it used and somebody has previously put something like Barrs No Leaks into your coolant tank and made a mess of things.

i'm still going with the impeller. Sorry... it just slips/cracks/breaks on so many german cars (not just VAG).

 

[Pabs]

no mate, if u read the rest of my threads on this you'll see that my thermostat was fine, but was replaced with brand new unit anyway. Hasnt made any difference.

Also not impellar. Brand new water pump about 2k miles ago, and also a metal version, not plastic.