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Tom Fenton

205 Gti 1600 Suspect Overheating

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Tom Fenton

This has got me stumped so have a read through and if anyone has any brainwaves let me know.

My laser 1600 GTI, totally standard. In 2013 it had new radiator, fan switch, hoses, water pump and heater matrix.

With this fine it always ran very cool on the gauge, just above the second line.

All great until last Sunday. I'd done 40 odd miles the previous day no issues. All of a sudden temperature starts to rise. Even when moving at cruising speed the temp was up above the 5th marker. I usually like to see them run around the 4th marker for normal temp.

So I've started changing bits.

So far, thermostat, water pump, sender for gauge, expansion tank cap.

All make no difference.

Removed rad flushed through. Earthed gauge wiring to test and seems ok.

Starts and runs fine. Doesn't use coolant. System is very clean tbh, I've only ever used decent coolant in it.

Rad fan switch appears to have packed in as slow doesn't come in until the gauge is past the 6th notch.

The only thing I have left as a suspect is the gauge in the dash or maybe the head gasket.

However all the XU failed gaskets I have come across showed as massive pressure in the cooling system followed by it shoving all the water out and rapid overheating.

This doesn't feel like that- it doesn't over pressure the cooling system and doesn't spit its coolant out either.

What's got me stumped is at gentle cruise I would expect it to run cool and it doesn't.

 

So any thoughts or experiences welcomed! It's doing my head in now tbh!!

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Anthony

Is there anything else supporting that the engine is actually running hotter - higher oil temperature or measured coolant temp with an IR thermometer for example?

 

It doesn't seem coincidental to me that the gauge is showing hotter both on cruise and when the fan eventually kicks in, so I don't think I'd be so quick to blame the thermoswitch for the later (assuming both slow and fast settings are working).

 

If you leave engine idling from cold, how hot does the gauge read when the thermostat opens and the radiator gets warm? That should typically be around 4th mark on the gauge (11 o'clock ish) with a standard thermostat as you know.

 

I agree with your comment about head gaskets failure - like you, every one I've seen an an alloy XU has always shown itself with over-pressurising the cooling system and/or unexplained coolant loss, never just unexplained hot running with no other symptoms.

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dobboy

I'd say dash gauge itself, and your fans are actually coming on when they should but the dash is reading incorrectly.

 

Especially as you've got the same readings with two senders, which rules a sender out, and there's no obvious HG failure indicators.

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Tom Fenton

Is there anything else supporting that the engine is actually running hotter - higher oil temperature or measured coolant temp with an IR thermometer for example?

 

It doesn't seem coincidental to me that the gauge is showing hotter both on cruise and when the fan eventually kicks in, so I don't think I'd be so quick to blame the thermoswitch for the later (assuming both slow and fast settings are working).

 

If you leave engine idling from cold, how hot does the gauge read when the thermostat opens and the radiator gets warm? That should typically be around 4th mark on the gauge (11 o'clock ish) with a standard thermostat as you know.

 

I agree with your comment about head gaskets failure - like you, every one I've seen an an alloy XU has always shown itself with over-pressurising the cooling system and/or unexplained coolant loss, never just unexplained hot running with no other symptoms.

Its hard to know what it has ever run at temp reading in celcius wise.

 

I did some tests last night with the IR thermometer and with the stat open and showing 90-ish on the radiator surface the gauge was showing above the 5th marker. This was with it sat idling from cold. The rad fan didn't cut in on slow at this point which I would normally expect it to- I'd have to look up the temp readings but I'm sure the slow should be running by then.

 

However even if I sort the fan out it doesn't account for it being hot when cruising along at steady speed on the motorway for example.

 

I've rooted through my bits and found another gauge so I'll have to change it and see.

 

Steve Heath has a block tester so I think that's also next at least if only to rule out the gasket.

I'd say dash gauge itself, and your fans are actually coming on when they should but the dash is reading incorrectly.

 

Especially as you've got the same readings with two senders, which rules a sender out, and there's no obvious HG failure indicators.

Lets hope so!

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tartanbloke

Alternatively, completely out there suggestion but given the current heat experienced now as well at the weekend, the air flow going through the radiator was not cool enough to reduce the temperature of the engine?

 

I have found my fan kicking in a lot earlier and more often that usual over the past week even on dual carriageway doing 30mph in rush hour traffic.

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Tom Fenton

Alternatively, completely out there suggestion but given the current heat experienced now as well at the weekend, the air flow going through the radiator was not cool enough to reduce the temperature of the engine?

 

I have found my fan kicking in a lot earlier and more often that usual over the past week even on dual carriageway doing 30mph in rush hour traffic.

I had considered this, but even the other night about 10pm when it was nice and cool it was still up high on the gauge when doing a steady 60mph on a quiet motorway, e.g. there should have been ample cool airflow.

 

The other symptom was that even with the gauge indicating hot e.g. nearly the 6th marker, the heater when turned to fully hot was "mildly" warm at best.

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dobboy

Just a thought.

 

I think I read/seen a drawing somewhere that these gauges actually work by two resistances in parallel (sender paralled up with another fixed resister at the clocks), with the sender resistance changing/reducing with heat, making a variable overall resistance to the presumably coil of the gauge.

 

Does the temp gauge start at zero on cold start up, or start higher than you'd expect initially?

 

If you disconnect your sender and measure the resistance up the sender wire to earth, I can measure mine for you and see if there's any notable difference.

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Anthony

The other symptom was that even with the gauge indicating hot e.g. nearly the 6th marker, the heater when turned to fully hot was "mildly" warm at best.

Assuming that the heater used to be good, that sounds like an important clue, as that suggests limited coolant flow through the matrix at least.

 

Given that you've replaced the water pump and an airlock seems unlikely with how many times you've presumably drained and refilled/bled the cooling system, that points to a blockage somewhere to me.

 

In the heat last week coupled with the coolant temperature being that hot, the heater turned up to max should be bordering on unbearable.

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dcc

Tom whats the condition of the wiring on the multiplug above gearbox?

 

I bought a stand alone temp sensor a few years ago to discount overheating on an old 205 - turned out to be a wiring fault. The cause was cruddy connectors on said multiplug

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Anthony

I bought a stand alone temp sensor a few years ago to discount overheating on an old 205 - turned out to be a wiring fault. The cause was cruddy connectors on said multiplug

You sure about that Dan? Bad wiring connections will logically cause higher resistance and thus a lower gauge reading.

 

To make it look like it was overheating, you'd need lower resistance - hence shorting it to earth (zero resistance) makes the gauge read maximum.

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Tom Fenton

Just a thought.

 

I think I read/seen a drawing somewhere that these gauges actually work by two resistances in parallel (sender paralled up with another fixed resister at the clocks), with the sender resistance changing/reducing with heat, making a variable overall resistance to the presumably coil of the gauge.

 

Does the temp gauge start at zero on cold start up, or start higher than you'd expect initially?

 

If you disconnect your sender and measure the resistance up the sender wire to earth, I can measure mine for you and see if there's any notable difference.

It does start at "zero". Also changing the sender for a new one hasn't changed anything.

 

 

Assuming that the heater used to be good, that sounds like an important clue, as that suggests limited coolant flow through the matrix at least.

 

Given that you've replaced the water pump and an airlock seems unlikely with how many times you've presumably drained and refilled/bled the cooling system, that points to a blockage somewhere to me.

 

In the heat last week coupled with the coolant temperature being that hot, the heater turned up to max should be bordering on unbearable.

I haven't flushed the heater itself, I guess I can do so. I flushed it from the thermostat housing through to the bottom hose both ways, got a "decent" flow in both directions. Water pump is new replaced on Tuesday, didn't make a change. Filling it from the stat housing with the bottom hose blocked with my hand it filled up and also filled back to the header tank.

 

 

Tom whats the condition of the wiring on the multiplug above gearbox?

 

I bought a stand alone temp sensor a few years ago to discount overheating on an old 205 - turned out to be a wiring fault. The cause was cruddy connectors on said multiplug

I've checked this last night, it looks good TBH. I wired from the sender to the plug to bypass and the reading didn't alter. I'll bell it from the dash to the sender to check resistance but I think its OK.

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dcc

Yes Ant, it was on a 1.9 gti I had from your way a while ago. It read higher than it was actually showing, after cleaning the spades with emery cloth and the earth terminals it was back where to be expected. I was concerned as it had only just had a new hg

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tartanbloke

It does start at "zero". Also changing the sender for a new one hasn't changed anything.

 

 

 

I haven't flushed the heater itself, I guess I can do so. I flushed it from the thermostat housing through to the bottom hose both ways, got a "decent" flow in both directions. Water pump is new replaced on Tuesday, didn't make a change. Filling it from the stat housing with the bottom hose blocked with my hand it filled up and also filled back to the header tank.

 

 

 

I've checked this last night, it looks good TBH. I wired from the sender to the plug to bypass and the reading didn't alter. I'll bell it from the dash to the sender to check resistance but I think its OK.

Interestingly, I had a luke warm heater in my old mini and when I flushed out the heater matrix a glob of radweld came out and then found that it had also blocked most of the hoses, which then made it run much better and the temperature gauge never moved as much as it did.

 

This is why I never use radweld or recommend it as it just blocks everything up.

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Tom Fenton

Update

Hours and hours wasted

 

In summary I think it's a duff thermostat.

Gauge reads 6th mark, but a run on motorway and pull over and gun the radiator it is at 80 degrees so is cooling well.

 

Tried another set of clocks which read the same. Tried a wire direct from sender to clocks to eliminate the loom, no change.

 

After much messing about including pulling the stat housing off to jet wash through the block, I decided to try it with no thermostat in.

Lo and behold it's fine. Doesn't get hot. Drive it hard sit it idling for 10 min and the gauge climbs up to the 4/5th notch. Drive it above about 30mph and within 1/2 a mile the gauge drops back to 2 notches.

Good news is it looks like the engine is ok.

 

Had a look at the stat I changed last week. It's an 88. Thinking of trying a different brand and 82 degree stat next.

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jackherer

It might be interesting to put the stat in a pan of water with a thermometer, heat it up and see what it does...

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toolie72

It might be interesting to put the stat in a pan of water with a thermometer, heat it up and see what it does...

Agree

I personally thought that thermostats were designed to fail "open"

If that's not the case then it's just more to check-pants

 

Thumbs up for problem solving

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Tom Fenton

It might be interesting to put the stat in a pan of water with a thermometer, heat it up and see what it does...

I did this last week and it did open. I didn't have a thermometer I trust to tell me at what temperature though.

 

The bit that eventually led me to it was that the header tank was getting roasting hot, from the small bypass line feeding water from the stat housing through the throttle body back to the header tank.

Next steps are an 82 deg stat and another rad fan switch as that's dead too.

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Anthony

If it is a thermostat issue, I wonder why the heater isn't also hot?

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Tom Fenton

I flushed it out, at first it was flowing water but seemed quite a bit of pressure in the hose. A few goes each way and it got easier. It was a new matrix at the same time as everything else!

Anyway will see how it is with a cooler stat in that hopefully opens properly.

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Tom Fenton

Just to finish.

 

82 deg "Gates" thermostat fitted this afternoon. Lo and behold sorted.

 

New fan switch also fitted, the slow speed comes in a little late for my liking but at least it's all working now.

 

Damn cars!

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tartanbloke

Just to finish.

 

82 deg "Gates" thermostat fitted this afternoon. Lo and behold sorted.

 

New fan switch also fitted, the slow speed comes in a little late for my liking but at least it's all working now.

 

Damn cars!

Stops you getting bored?

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