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Topic: Over heating (Read 899 times) previous topic - next topic

Over heating

Hello Folks,

Not been as active on here as I'd like. Such is life.

I have an issue. My H reg mk2 GTI 8v Digifant is over heating. Essentially the fan wasn't coming on. This has been a gradual thing, as before the fan would kick in but rather late, by which point the temp gauge was flashing at me. It'd cool down once the fan kicked in, but the fan would be on almost constantly. Motorways and fast moving traffic it was fine of course.

Now it has been a little ropey up to this point, with it stalling when coming to a junction, whilst the engine is cold. Once warmed up it was fine, idles fine, albeit when the revs drop it would stutter everso slightly a moment before regulating itself again.

Anyway to cut a long story short. The fan isn't kicking in. Now the fan is only a few months old so I don't think it's that. It had power going to it when the AA tech tested all the connections. (I came off the m6 on my way up to Mancester when traffic was gridlocked)

I have drained the coolant to take a look at the 'stat. (removing the PAS pump was a bit of a nightmare). I have tested the 'stat and it starts to open at the tempt set by it at 87c. So it's not that. So now I'm thinking it's either the rad sensor, or the tempreture sender unit or the thermo switch? I have the later version which is 2 sensors going in to a hose connector on the side of the engine with the spark plugs.

I have heard horror storys about these sensors, namely the blue one. Haynes calls it the ECU temp sensor. What I am unsure about is would it even play a part with the fan? I don't know how interconnected these are given it's an old car. I would've thought the fan would run off from the rad sensor, which is linked to the overall coolant temp, and works in tandem with the 'stat?

Basically where I am now is I don't want to waste time and money sticking coolant back in, putting the PAS pump back on, and then pissing about takings things off again, like the rad sensor. (Can't actually get it off as I don't have a big enough spanner/socket.) I also hear I have to reset the ECU after swapping the ECU temp sensor.

I will attached a link to some images, including the old and new one. The old one does look a bit knackered and is probs the original. It's VAG and VDO brand. The new OEM one I have bought looks cheap in comparison, although it certainly wasn't to buy.  :D

Bascially can anyone give me any suggestions or tips? I want to get my baby back on the road as I miss driving it! :(

Hopfully the link works!

https://imgur.com/a/CBJogcs

Re: Over heating

Reply #1 –
Bumping this topic, because I need to start putting things back together.

Re: Over heating

Reply #3 –
If your fan has power it seems its missing the command to run which surely has to be the radiator temp sensor. I cant see how if the car is cold the cooling fan issue causes erratic running.
scs  

Re: Over heating

Reply #4 –
Yup. That works.

So I managed to get the rad sensor off today. It must be 29mm because 30 is the next size up that fits, albeit loose. I had to use an adjustable as I have no spanner big enough, or socket deep enough.

It looks pretty manky to be honest so it's probs that, or an amalgamation that and the ECU temp sensor. Tbh I am just going to start throwing it back together now I think. I have pretty much eliminated all possible issues now anyway. It's not the fan,  it has a new rad sensor, new ECU temp sensor, I'm probs going to put the new thermostat on it too, even though the current one opens.

I have attached an image of the manky rad sensor.
https://imgur.com/a/HYOSFui

Re: Over heating

Reply #5 –
Quote from: scs on
If your fan has power it seems its missing the command to run which surely has to be the radiator temp sensor. I cant see how if the car is cold the cooling fan issue causes erratic running.
scs  

I agree, however from what I have read up on the subject, the ECU temp sensor seems to play a big overall part.
It could be the over heating issue WAS to do with the fan rad sensor, and the somewhat ropey running is not connected and just happends to be a knackerd ECU temp sensor.

Re: Over heating

Reply #6 –
Your radiator fan control is extremely basic ( but good basic).
It essentially runs a 12v supply from the battery, into the radiator switch.
Now the switch has three terminals, as does the fan.
When the switch goes above one temperature, it'll send the voltage to the low speed terminal on your fan.
When it goes above a second temperature, it'll send the voltage through the high speed terminal on your fan,

There is no interference from any of the blue senders or the ECU, it's completely stand alone.
Makes is a great system for engine conversions.
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Re: Over heating

Reply #7 –
Quote from: Monkey on
Your radiator fan control is extremely basic ( but good basic).
It essentially runs a 12v supply from the battery, into the radiator switch.
Now the switch has three terminals, as does the fan.
When the switch goes above one temperature, it'll send the voltage to the low speed terminal on your fan.
When it goes above a second temperature, it'll send the voltage through the high speed terminal on your fan,

There is no interference from any of the blue senders or the ECU, it's completely stand alone.
Makes is a great system for engine conversions.
Just a note in addition some early cars only have a single speed fan and a 2 pin rad thermostat/switch. I recently brought the wrong rad fan switch as didn't read the detail properly.

Re: Over heating

Reply #8 –
UPDATE:

So I'll address the comment about the fan. This noisy as f**k fan has but one speed. It's louder than the damn engine, but does work. Though reading what as been said, I probs need a 2 speed.

HOWEVER..

After putting it all back together, putting new sensors on. It is running fine, and actually slightly better. The temp needle sits better, it and revs better, and it isn't over heating. Doesn't even flash at me before the fan kicks in like it used to.

The thing that has me perplexed is the ammount of coolant it took. The capacity is about 6.3L, yet it only took 5L. Now the only logical reason is that it still had fluid in the system, but I flushed and then blew air through the system. So I have no idea why. Driving it for a bit, and giving it some, it remained at the correct level, and was totally fine. Which has left me a little sus.  ::)

Sadly due to the current fuel issue at the pumps, I can't get any Vpower, or premium fuel for it, and it's close to red on the gauge. So when I can, I will give it a proper run.

I WILL address that fan topic and look at 2 speed fans. The original that was on it started squeeling like a pig, but was still working. Because it's a sealed unit, I can't get it repaired. :(

Re: Over heating

Reply #9 –
Quote from: DerKommissar on
UPDATE:

So I'll address the comment about the fan. This noisy as f**k fan has but one speed. It's louder than the damn engine, but does work. Though reading what as been said, I probs need a 2 speed.

HOWEVER..

After putting it all back together, putting new sensors on. It is running fine, and actually slightly better. The temp needle sits better, it and revs better, and it isn't over heating. Doesn't even flash at me before the fan kicks in like it used to.

The thing that has me perplexed is the ammount of coolant it took. The capacity is about 6.3L, yet it only took 5L. Now the only logical reason is that it still had fluid in the system, but I flushed and then blew air through the system. So I have no idea why. Driving it for a bit, and giving it some, it remained at the correct level, and was totally fine. Which has left me a little sus.  ::)

Sadly due to the current fuel issue at the pumps, I can't get any Vpower, or premium fuel for it, and it's close to red on the gauge. So when I can, I will give it a proper run.

I WILL address that fan topic and look at 2 speed fans. The original that was on it started squeeling like a pig, but was still working. Because it's a sealed unit, I can't get it repaired. :(
Don't forget you need to check the levels when cold.
The thermostat could have been trapping air until it opened up.

Re: Over heating

Reply #10 –
The is usually some amount of water held in by the water pump unless that was removed as well.

Re: Over heating

Reply #11 –
Quote from: sly_gti on
Quote from: DerKommissar on
UPDATE:

So I'll address the comment about the fan. This noisy as f**k fan has but one speed. It's louder than the damn engine, but does work. Though reading what as been said, I probs need a 2 speed.

HOWEVER..

After putting it all back together, putting new sensors on. It is running fine, and actually slightly better. The temp needle sits better, it and revs better, and it isn't over heating. Doesn't even flash at me before the fan kicks in like it used to.

The thing that has me perplexed is the ammount of coolant it took. The capacity is about 6.3L, yet it only took 5L. Now the only logical reason is that it still had fluid in the system, but I flushed and then blew air through the system. So I have no idea why. Driving it for a bit, and giving it some, it remained at the correct level, and was totally fine. Which has left me a little sus.  ::)

Sadly due to the current fuel issue at the pumps, I can't get any Vpower, or premium fuel for it, and it's close to red on the gauge. So when I can, I will give it a proper run.

I WILL address that fan topic and look at 2 speed fans. The original that was on it started squeeling like a pig, but was still working. Because it's a sealed unit, I can't get it repaired. :(
Don't forget you need to check the levels when cold.
The thermostat could have been trapping air until it opened up.

Yup. Still at the same level. Must've had some fluid in the block or pump, like you said. I will continue to monitor but it seems all good.