Overheating warning on acceleration 2.4 Petrol Cab

[Cabbyfan]

Hi all,

Been a long time since I posted so hope all is well.

My beloved A4 Cab is overheating on acceleration... 2.4 V6 petrol. I did the cambelt plus stat and pump almost 2 years ago but I expect one of them has failed.

Any ideas, no fault codes .

 

[Garrett 69]

Daft question but you have checked the coolant and that the fan is working?

 

[Cabbyfan]

Daft question but you have checked the coolant and that the fan is working?

Hi, I have yes. Header tank level is fine and fan cuts in as expected.

What I did notice is the top rad hose doesn't seem to get that hot.

 

[Stonedofmoo]

Did the pump have metal or plastic impeller blades?

 

[Cabbyfan]

Did the pump have metal or plastic impeller blades?

I can't remember, it's 2 years since I did it. I expect plastic... the dreaded blade slipping issue I expect

 

[Stonedofmoo]

I can't remember, it's 2 years since I did it. I expect plastic... the dreaded blade slipping issue I expect

I have heard of plastic blades breaking off and causing this issue, but I think that's highly unlikely after only 2 years, yet I'm struggling to think what else could be causing it. Oil and coolant is clean? (Thinking head gasket issues)

 

[Cabbyfan]

Hi, oil and coolant seem unchanged. VCDS lite doesn't find any obvious sensor issues.

My last A4 saloon blew its head gasket because the pump failed. I remember asking Audi if they could fit one with metal blades and they said no.

My only other thought was airlock but doubt it's that.

 

[Cabbyfan]

Got it apart. Water pump is fine (metal impeller) so that's not the issue. Might be thermostat.

While it's in bits I may as well rinse out the heater matrix, radiator etc.

 

[Cabbyfan]

Stuck my thermostat in a pan of water and it opens and closes fine.... grrrrrr

 

[Stonedofmoo]

Then replace the temperature sensor to ensure what you are seeing is correct.

 

[Cabbyfan]

Then replace the temperature sensor to ensure what you are seeing is correct.

Good plan. I assume you mean the one at the back near the bulkhead?

 

[Stonedofmoo]

I'm not familiar with your particular engine, but on most vag engines of this era there is a single sensor, black or green if it's been replaced previously. They're only cheap, you can pickup a good quality febi bilstein sensor for around £15 new

 

[Cabbyfan]

On mine, there are two. One in the bottom hose on the radiator which isn't connected to anything and the one at the back. I will swap them over before I fill the system back up cheers.

 

[Garrett 69]

I'd say you're looking at a major airlock somewhere.

 

[Cabbyfan]

I'd say you're looking at a major airlock somewhere.

I think its certainly a possibility. Its been fine for 2 years so it's odd to get an airlock now. Given its in bits anyway now I've bought a new timing belt too so hopefully this weekend I will get it back together and let you all know.

 

[Cabbyfan]

Its back together. New belts, stat and pump. Bled pipe at heater bulkhead lots of pressure. I can't open the bleed valve at the front as it's been rounded.

Temp gauge still shoots up as soon as I accelerate and dash lights up.

I'm going to try a new Temp sensor. If that doesn't fix it then it's going for scrap.

 

[Stonedofmoo]

That's so bizarre, try the sensor. Also I'd consider flushing the radiator and cabin heater core if for no other reason than to check the water flows through without blockage

 

[Cabbyfan]

That's so bizarre, try the sensor. Also I'd consider flushing the radiator and cabin heater core if for no other reason than to check the water flows through without blockage

Can you recommend a sensor?
I flushed out the radiator before I refitted it. What is odd is when I filled the system there was no coolant in the heater matrix feed so I put a funnel in it and filled it. Heater is working so I'm with you it's either an sensor or blockage/ airlock. It's just a pity I can't open the front bleed screw.

 

[Stonedofmoo]

Regarding that bleed screw I'd definitely change that pipe or find someone to weld a nut to it so you can undo it, it's there for a reason..

Call Audi for the sensor part number and then search for a much cheaper pattern part online!

 

[Cabbyfan]

Regarding that bleed screw I'd definitely change that pipe or find someone to weld a nut to it so you can undo it, it's there for a reason..

Call Audi for the sensor part number and then search for a much cheaper pattern part online!

Totally. I'm going to cut a slot and see if I can get it out with a flat blade screwdriver.

 

[Cabbyfan]

So, disconnected the 2 pipes to the heater matrix and flushed with cold water in both directions multiple times. Nothing obvious came out and coolant was clean.

Reconnected, lifted the expansion tank a couple of inches and topped up the system.

Started up, bled at the matrix hose. Can't get it to spurt out if the hole.

Initially on test drive looked fine then temp rises and alarm goes off but was a lot less frequent . Lots of heat from heater then more frequent alarms and noticed no heat from heater. Stopped and heat returned from heater on idle, engine fan is on. What's odd is it only overheats on acceleration not revs at idle.

So I'm pretty sure I've got a blockage and an airlock in the engine bay.

Starting to really hate this car now.

 

[Cabbyfan]

Update....

Took it for a test drive last night after opening the expansion tank and starting it cold. Some coolant rose up when reving. Pulled heater hose back and strong jet came out so all good. Cap back on.

Test drive initially ok but then needle again started to quickly rise above 90 degrees on acceleration.
Plugged VCDS-Lite in and logged engine temp and instrumentation coolant temp while on short drive.

Engine ranged from 86 to 102 but also noticed it randomly shows 70 which could be sensor or air pocket.

Instrument temp was higher 115 to 125

Thought is maybe actually the coolant is fine, but dodgy sensor reading is confusing the instrument panel and triggering the alarm.

 

[Cabbyfan]

I think I've fixed it ! New CTS fitted in less than 30 mins. I did notice the level in the expansion tank dropped by about half when I removed the sensor so I'm not ruling out airlock as well.

Once warm took vcds readings and the instruments reading is much lower and the engine one is more stable too.

So hopefully all is well. It's even got heat coming out of all the vents too.

Thanks for the help all.

 

[Stonedofmoo]

CTS being the temperature sensor?

 

[Cabbyfan]

CTS being the temperature sensor?

Yup,the one at the back of the engine. Pretty easy to replace as it happens.