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Old 14th November 2018, 19:12   #1
macafee2
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Default symptoms of stuck thermostat

How long does a diesel 75 take to warm up, if the thermostat is stuck open? Google maps shows I did over 20 miles and the gauge still did not get to 9 o'clock, this seems and awfully long time

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Old 14th November 2018, 19:15   #2
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Sounds like the usual o.e.m stat issue mate. Bung 1 in the top cooling hose it works just fine.
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Old 14th November 2018, 19:28   #3
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Originally Posted by macafee2 View Post
How long does a diesel 75 take to warm up, if the thermostat is stuck open? Google maps shows I did over 20 miles and the gauge still did not get to 9 o'clock, this seems and awfully long time

macafee2
whilst it does sound like an early opening thermostat, forget the gauge and use the OBD to rule out a (very unlikely) faulty gauge.

As far as time goes, a lot depends on how the car is driven, and ambient temps will have an effect to a certain degree. I would suggest, 3 miles of 40mph driving with minimal acceleration, you should be up to around 70-75 degrees (the 9 o clock position starts around 75 degrees , and up to 105 I believe), then a further 2-3 miles of the same should see you at 84-86. This is how my commute works, after this I would be onto the motorway, and accelerate firmly to 70, 88 degrees, after about 1/2 a mile.

It would be important to note, I have an 89 degree Wahler inline stat, other stats I have used, opened lower. The lower opening to the stated rating of the (inline) stat, I believe is due to its location. (fit an 86 degree stat, and I would expect it to show opening at around 84 degrees on the OBD)
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Old 14th November 2018, 20:13   #4
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whilst it does sound like an early opening thermostat, forget the gauge and use the OBD to rule out a (very unlikely) faulty gauge.

As far as time goes, a lot depends on how the car is driven, and ambient temps will have an effect to a certain degree. I would suggest, 3 miles of 40mph driving with minimal acceleration, you should be up to around 70-75 degrees (the 9 o clock position starts around 75 degrees , and up to 105 I believe), then a further 2-3 miles of the same should see you at 84-86. This is how my commute works, after this I would be onto the motorway, and accelerate firmly to 70, 88 degrees, after about 1/2 a mile.

It would be important to note, I have an 89 degree Wahler inline stat, other stats I have used, opened lower. The lower opening to the stated rating of the (inline) stat, I believe is due to its location. (fit an 86 degree stat, and I would expect it to show opening at around 84 degrees on the OBD)
obd? is that the on board readout via the ipk screen?
I have seen threads about how to access it but have never been able to take it onboard.

The car was driven at 2500 plus revs for the majority as I had used injector cleaner and it was at worst chilly, no frost on the windscreen when started

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Old 14th November 2018, 20:14   #5
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Originally Posted by macafee2 View Post
How long does a diesel 75 take to warm up, if the thermostat is stuck open?

Basically, forever.

It never warms up to 'normal' running temperture. The reason is that the 'failed' thermostat starts opening at too low a temperature, so the engine is being cooled when it should be warming up. Typically, the stat doesn't stick open and will always fully close again on cooling. The fact that coolant starts circulating too early, no matter how slowly, means the engine never warms up in typical running conditions.



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Old 14th November 2018, 20:20   #6
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thanks T-cut, I was suspecting a stuck stat but just felt that with the revs, distance and time it should have warmed up.

more king money on this blessed car. The fact it passed its mot is remarkable

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Old 15th November 2018, 12:54   #7
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To find out your car's actual running temperature you can access and run the car in diagnostic mode:

Hold down the trip meter button for 6 seconds.

Push it until number 19 appears

Push again when 'log off' appears (will alternate between log off and log on)

Push again to menu 7 and leave it. if the car has been standing it will say '015' which is possibly the test signal.

My thermostat had just started to stick open and the warmest the car got was 75 degrees.

Now that I have fitted a DMGRS inline thermostat, the temperature behaves as expected. When the engine is under load it reaches 88 degrees and then dips to about 79 before settling again at 82, which says to me that the engine is now cooling as expected.

As said though, diesels take a time to warm up - mine has only just reached operating temperature on my 8 mile morning commute on a mixture of 30, 40 and motorways.
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Old 16th November 2018, 00:28   #8
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Diagnostic Mode How To: https://www.the75andztclub.co.uk/for...ode+simplified


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Old 16th November 2018, 10:08   #9
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I've now printed a copy

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Old 19th November 2018, 10:44   #10
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While opinion has been divided since their 'discovery', I've yet to have problems running a top hose thermostat in any of my fleet - including a fully loaded up, remapped ZT-T being shoved down the Autobahn at 'brisk' speeds

Bang on 90 degrees the entire time.
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