Mk 4 Golf GTI - Overheating, running out of ideas???

[Sampr96]

Hi everyone

Hope I've managed to find the correct place for posting this, gonna see whoever can cast they're knowledge on this problem as I'm having a hard time trying to establish what on earth is wrong with this car.

So I've got a Mk 4 Golf on an 52 plate on about 150,000. This car seems to overheat when under any load, I can drive around town and small distances but am pushing my luck when underload, the dial slowly shoots up to 130 Degree's.

So, in regards to what I've done:

1I have just forked out the cash to get the waterpump, and cambelt changed. Was under the impression that the pump just wasn't pushing it around the system enough. This has not solved it, still overheating.

2 Before the water pump etc, I have had the heater matrix replaced. Still no luck.

3 I have had the coolant system "sniff" tested in regards to seeing if any hydro-carbons are getting in, in which they're not. This to me would say the head gasket is good.

4 The Thermostat has been taken out, but not replaced. This was unknown to me until I asked the previous owner. Would you say missing this would cause such an issue?

Now, I believe I have included all the details there, I don't think I'm missing anything. Here's what my possible solutions are:

Solution 1
The Radiator is dead or blocked. I say this because the bottom hose of the radiator is cold. Even when the car has been overheating its still cold. I'd surly expect to see some temperature in the hose?

Solution 2
Either its a cracked Piston, or head gasket. I am assuming solution 1 is the best?

Don't wanna do the radiator only to find out its no good neither. The coolant light comes on, in which I stop, pull over, as soon as I release the pressure on the expansion tank, all the coolant comes straight back again.

Guys/Gals, give us some idea's? I'm completely stumped on this one. I've forked out the cash for the water pump etc, kinda don't wanna do the same.

Any help, or opinion, its massively appreciated!

[colin_p]

Is it overheating?

The coolant temperature sensors on that era VAG cars are notorious for failing, often giving erratic readings.

If it were mine I'd replace both the thermostat and the temp sensor whilst it is drained down. Are you absolutely confident that the water pump was changed?

And to confirm, is it a 1.8t or a 1.9 TDI

[GreenV8S]

If the bottom hose is cold then you don''t have coolant flowing through the radiator, which would inevitably lead to overheating.

Does the cabin heater blow hot? If so that proves you at least have some coolant circulating through the engine.

[mercedeslimos]

If it's a 1.8 20vT then likely it will be a cracked cylinder head. See loads of these. on a TDI, a cracked piston would cause this too. Neither engine is expensive secondhand, however.

[227bhp]

Put a thermostat in it, it's the most likely, the easiest and cheapest.

[Matt_E_Mulsion]

If there is no thermostat and the bottom hose is still cold when the car is 'overheating' then there can't be any flow going through the radiator. I'd change that next.

[GreenV8S]

227bhp said:

Put a thermostat in it, it's the most likely, the easiest and cheapest.

This. You may find that when the stat opens the circuit to the radiator, it also closes the bypass. With the stat housing empty the coolant will be free to follow the path of least resistance, which will be the bypass.

[Matt_E_Mulsion]

If the thermostat was already missing that says to me that the previous owner has had cooling system issues with it that they didn't want to or manage to solve.

[Sampr96]

Hi guys,

Massive shout to those giving me some ideas.

As for the car forgot to mention it's the 1.9 GTDI.

I'd rarely get some heat coming through the heater matrix, however not long after it blows cold with no heat..then proceeds to overheat. As mentioned, the hose on the bottom of the radiator is cold. As it gets closer to the engine obviously gets slightly hotter. The 2 pipes going into the heater matrix are warm/hot.

Also, in regards to the thermostat? Do you really reckon having this missing is causing that much of an overheating issue? I could be daft here but I honestly thought its not the end of the world for this to be missing?

I've heard that headgaskets or cracked piston heads are rare on this. Based on the sniff test, Id be inclined to write off it being a headgasket.

It drives and pulls fantastic, just frustrating this overheating issue.

[Coilspring]

Does the heat from the engines feel correct to the information from the gauges? Got an ir thermometer to test heatflow around the engine/hoses?

Does the rad fan cut in? At what temperature?

Disconnect the 2 heater hoses and join them together temporarily, do the hoses get hotter?

Sounds more like restricted flow than anything else, but dont discount head/block issues yet.

[GreenV8S]

Sampr96 said:

Do you really reckon having this missing is causing that much of an overheating issue?

I don't know enough about that cooling system to know whether it would cause these specific symptoms, but on some systems it would. You need a stat in any case, so get that sorted and see whether it helps. By now it's possible that the overheating has damaged the head gasket even if HGF is not the original cause of the overheating, but either way it makes sense to get the stat sorted.

[OnTheEdge]

GreenV8S said:

Sampr96 said:

Do you really reckon having this missing is causing that much of an overheating issue?

I don't know enough about that cooling system to know whether it would cause these specific symptoms, but on some systems it would. You need a stat in any case, so get that sorted and see whether it helps. By now it's possible that the overheating has damaged the head gasket even if HGF is not the original cause of the overheating, but either way it makes sense to get the stat sorted.

I'm 95% sure the 1.9 PD does have a bypass circuit that is closed by the thermostat opening. Irrespective you shouldn't run an engine without a thermostat, at best it will make the engine run cold and increase wear and fuel consumption.

[GreenV8S]

OnTheEdge said:

I'm 95% sure the 1.9 PD does have a bypass circuit that is closed by the thermostat opening. Irrespective you shouldn't run an engine without a thermostat, at best it will make the engine run cold and increase wear and fuel consumption.

I agree.

[Sampr96]

Update..


So I have replaced the thermostat which was previously missing and it’s made no difference. When under load (going up hills, motorway etc) the temperature shoots up.

I have done a radiator flush which seems fine. No block in the radiator. I have done a flush on the new heater core, all seems fine.

I have put water in just to see if any water is making it to the heater core and it doesn’t seem like there is? Hence why even when overheating I’m still blowing cold air.

Any advice?

[Coilspring]

Sampr96 said:

Update..


So I have replaced the thermostat which was previously missing and it’s made no difference. When under load (going up hills, motorway etc) the temperature shoots up.

I have done a radiator flush which seems fine. No block in the radiator. I have done a flush on the new heater core, all seems fine.

I have put water in just to see if any water is making it to the heater core and it doesn’t seem like there is? Hence why even when overheating I’m still blowing cold air.

Any advice?

Is the water pump actually moving any water? Got an ir thermometer to check at various points whats happening ?

[colin_p]

There are only two things left;

Coolant temp sensor is faulty, as I've said above these fail regularly and provide false readings.

Head gasket failure. PD's are difficult to diagnose for this but their mode of failure is cylinder to coolant passage which pressurises the cooling system and stalls the circulation. When giving it beans this can even overcome the action of the water pump hence the rapid temp rise.

[Matt_E_Mulsion]

There is enough water in it, ie it's been bled properly hasn't it???