Author Topic: Coolant Temp not holding 90  (Read 6742 times)

Offline Second

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Coolant Temp not holding 90
« on: July 27, 2019, 04:37:02 PM »
R-Tech advised me last month that my thermostat needed replacing as my coolant temp wasn’t holding at 90c. I took my car in to my local garage last week and had it done, but the temperature is still dropping off to ~80 when I’m just cruising along at a set speed on the highway :thinking: Any ideas what the problem could be?

Offline bobby_fodge

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Re: Coolant Temp not holding 90
« Reply #1 on: July 27, 2019, 05:53:53 PM »
Coolant temp sensor?

Offline muff1991

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Re: Coolant Temp not holding 90
« Reply #2 on: July 29, 2019, 10:46:04 AM »
some engines have 2 thermostats, have you got a second? if not.. then go with the coolant temp sensor.

Offline Octoparrot

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Re: Coolant Temp not holding 90
« Reply #3 on: July 29, 2019, 12:11:11 PM »
Maybe check to make sure they actually did replace the thermostat?

Offline RedSwede

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Re: Coolant Temp not holding 90
« Reply #4 on: July 29, 2019, 01:00:00 PM »
I've had some issues here.

Some time ago, noticed the temp was not at the full 90 on the dial. Checked it on the climate-debug-mode-thing, and was around 75. I duly booked it for a thermostat, got it back, and the temperature was holding steady at 90 on the dial. All good.

I later checked the climate temperature again, and it actually still only holds 83/84 never really beating 85 degrees. So obviously the thermostat had been changed, but it was still not 100%. Checking the climate engine temp after sitting overnight, it actually said 9 or 10, when the weather was 15 or 16 - so I thought I found the issue. Swapped the sensor for a cheap one off ebay, which then read the correct outside temperature. But would only get to 79/80 in driving. Argh!

I put the old one back, the dial sits in the middle (so ECU is out of warm up mode), and I don't worry about it too much, but I guess new thermostat and new sensor (VAG OEM I would say) would be step one.
« Last Edit: July 29, 2019, 01:01:46 PM by RedSwede »

Offline goku4ever

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Re: Coolant Temp not holding 90
« Reply #5 on: August 03, 2019, 02:06:01 AM »
R-Tech advised me last month that my thermostat needed replacing as my coolant temp wasn’t holding at 90c. I took my car in to my local garage last week and had it done, but the temperature is still dropping off to ~80 when I’m just cruising along at a set speed on the highway :thinking: Any ideas what the problem could be?
DSG or manual transmission?

Had the same issue, changed main thermostat and inline thermostat on my DSG. Temp sits at 93-95 on ecu


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Offline Second

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Re: Coolant Temp not holding 90
« Reply #6 on: August 03, 2019, 05:00:13 PM »
Coolant temp sensor?

I will try getting this replaced - hopefully that solves it!

some engines have 2 thermostats, have you got a second? if not.. then go with the coolant temp sensor.

How do I find out if I have 2?

Maybe check to make sure they actually did replace the thermostat?
I'm sure they did the work. I have the invoice and have been using them for years, so I know they are trustworthy.

I've had some issues here.

Some time ago, noticed the temp was not at the full 90 on the dial. Checked it on the climate-debug-mode-thing, and was around 75. I duly booked it for a thermostat, got it back, and the temperature was holding steady at 90 on the dial. All good.

I later checked the climate temperature again, and it actually still only holds 83/84 never really beating 85 degrees. So obviously the thermostat had been changed, but it was still not 100%. Checking the climate engine temp after sitting overnight, it actually said 9 or 10, when the weather was 15 or 16 - so I thought I found the issue. Swapped the sensor for a cheap one off ebay, which then read the correct outside temperature. But would only get to 79/80 in driving. Argh!

I put the old one back, the dial sits in the middle (so ECU is out of warm up mode), and I don't worry about it too much, but I guess new thermostat and new sensor (VAG OEM I would say) would be step one.
Glad to see someone else sharing my frustration! lol

R-Tech advised me last month that my thermostat needed replacing as my coolant temp wasn’t holding at 90c. I took my car in to my local garage last week and had it done, but the temperature is still dropping off to ~80 when I’m just cruising along at a set speed on the highway :thinking: Any ideas what the problem could be?
DSG or manual transmission?

Had the same issue, changed main thermostat and inline thermostat on my DSG. Temp sits at 93-95 on ecu


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It's a manual transmission.

Offline The Red Warrior

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Re: Coolant Temp not holding 90
« Reply #7 on: August 07, 2019, 09:48:56 AM »
If manual, then you’ll have two thermostats. A main and an inline. At least you will if it’s a 2005 till about 2007 I think. At some point I believe they did away with the inline thermostat. The main one is the one that keeps the temperature at 90°C (or thereabouts). Are you sure you’re mechanic changed that one and not the inline one?

Offline Octoparrot

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Re: Coolant Temp not holding 90
« Reply #8 on: August 07, 2019, 03:03:44 PM »
If manual, then you’ll have two thermostats. A main and an inline. At least you will if it’s a 2005 till about 2007 I think. At some point I believe they did away with the inline thermostat. The main one is the one that keeps the temperature at 90°C (or thereabouts). Are you sure you’re mechanic changed that one and not the inline one?

Not necessarily, mines a 2006 manual and only has the main thermostat.

Offline The Red Warrior

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Re: Coolant Temp not holding 90
« Reply #9 on: August 08, 2019, 02:00:01 AM »
Ah, ok.  Must have been the 2005 and perhaps early 2006 only then with with two.
There is a huge thread all about this on this forum already.

Offline Second

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Re: Coolant Temp not holding 90
« Reply #10 on: August 21, 2019, 10:58:41 AM »
I looked up the part they used online and it was the main thermostat which they replaced.

My car is a 2006 manual - no idea how many thermostats it has to be honest, or how I would check.

I had the coolant temp sensor replaced yesterday and it seems worse than before to be honest  :scared: Never seemed to reach 90C whilst driving and at one point it seemed to drop down to ~70c. It only seemed to pick up to 90C once I’d finished hooning it around and parked up.

How much of problem is this? What is it affecting negatively exactly?
« Last Edit: August 21, 2019, 11:01:56 AM by Second »

Offline f00glee

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Re: Coolant Temp not holding 90
« Reply #11 on: August 21, 2019, 12:54:33 PM »
Thread with location of inline stats on an early DSG. Not sure which of these locations would be right for an inline stat on an early manual car - check both?

https://www.mk5golfgti.co.uk/forum/index.php?topic=78341.0

MkV GTI, Tornado Red, 3-door, 06, R-tech Stage "1+"

Offline ljc19630

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Re: Coolant Temp not holding 90
« Reply #12 on: August 21, 2019, 05:16:14 PM »
Mines the same and not holding at 90. Drive up to R-Tech on Sat for K04 conversion work and was the first thing that Niki asked me. Said it was below 90 on motorway and when under normal driving sits even lower. He will replace thermostat while car is there


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Offline RedSwede

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Re: Coolant Temp not holding 90
« Reply #13 on: August 28, 2019, 04:01:22 PM »
I had the coolant temp sensor replaced yesterday and it seems worse than before to be honest  :scared: Never seemed to reach 90C whilst driving and at one point it seemed to drop down to ~70c. It only seemed to pick up to 90C once I’d finished hooning it around and parked up.

How much of problem is this? What is it affecting negatively exactly?

As you can read above, I had exactly this. Thermostat replaced, decent but not 100% improvement. New sensor, temperature lower...

A few questions:
1. Was it a genuine VAG sensor?
2. Are we talking 90 degrees on the dial/instrument cluster? Or on the climate control diagnostics? If it's reading 90 on the dial, just not on the climate, as I understand that is less of an issue. The dial is just some software indication, and if that is bang on vertical, it means that the ECU will be operating in its normal range - the main thing, really.

Offline Second

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Re: Coolant Temp not holding 90
« Reply #14 on: October 03, 2019, 03:25:23 PM »
Okay, so turns out the issue was that it was replaced with a non oem thermostat.

R-Tech fitted me the proper one prior to remapping and now it sits dead on 90C 100% of the time  :smiley: