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MK4 TDi - Temp issues.....


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#1 puzzle735

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Posted 09 January 2021 - 07:51 PM

Hi

 

About early Dec my MK4 TDi (130bhp) temp gauge started doing odd things.  It wouldn't get above 75 degrees, even after 30 miles.  Temp outside was cold, about 2 degrees but the temp outside has never made any difference to my temp gauge before.  Anyways, under load or off throttle, it made no difference atall.  

 

I've had the car 7 years and I did have to purchase a new temp sensor (green) about 6 years ago as the temp gauge was just dead, it didn't move.  Thinking that may be faulty and it was the cheapest thing to replace, along with losing the least anti-freeze, I set about changing it but got a Febi part for about £10 as VW wanted £38.57 plus VAT for this part.  When I replaced this originally with a VW part it was less than £10 at the stealer.  That didn't solve the issue and temp remained at 75.

 

I then decided to change the thermostat, stealer wanted £26.57 for the thermostat and £3.97 for the o-ring, both plus VAT!  So I got a Meyle part, I have got the correct part and it opens at 87c.  I filled the anti-freeze back up with ready mix G12+.  I did have to put nearly a full 5 litres in it after draining it.

 

Unfortunately, replacing the theromstat has made the car even worse, after 15 miles the temp gauge didn't move!  Over the next 15 miles it slowly crept up to the 3rd of the first 3 white marks that are close together at the bottom of the temp gauge.  So nowhere near the 75 that it was before!  

 

The hose that has a plastic union which bolts onto the thermostat housing has no temperature to it after 30 miles.  Top hose of rad is warm but not hot.

 

Car heater is barely warm, it was getting warmer before I changed the thermostat.  I can confirm there are no air locks as I bled the system and have topped up.  Since the 30 mile run, the level of coolant has remained constant.  

 

The car has done 138,000 miles and doesn't use or leak anti freeze.

 

I am guessing its either a genuine stat now or maybe the water pump?  

 

I've been running the car at about 75 degrees since early December and am now facing next week with next to zero temps with the car not warming up atall.  It hasn't warmed up in 30 miles today and its only 8 miles to work!  Will this damage the engine atall, should I take it off the road?

 

Any advice appreciated.  




#2 Imagewerx

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Posted 09 January 2021 - 08:23 PM

Your post has been moved.Always ask technical questions in the relevant technical section.



#3 ttg4l

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Posted 09 January 2021 - 09:07 PM

If it was the water pump, I'd have thought you'd get the opposite and you'd be overheating.

 

In my experience, aftermarket stats are okay, but aftermarket temp sensors are not. I've got a febi stat that was £8 ish from Amazon and it's been fine. And I've got a genuine temp sensor after the aftermarket ECP part started leaking into the loom.

 

What process did you use for bleeding the system? 



#4 puzzle735

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Posted 09 January 2021 - 11:43 PM

After refilling, I let it idle for about 15 mins with the expansion tank cap off and the heater on max. Every few mins I squeezed the radiator top hose and this made coolant go back into the expansion tank. Then suddenly all the coolant from the expansion tank disappeared so I topped up again. It did this twice, then I took it out and after about 5 miles checked the coolant and topped up again.
After that I went on the 30 mile run, after which the coolant had remained stable and I didnt need to top up.
I've put about 4.5 litres in.
Will running the car cold like this damage the engine?
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#5 seagull VW

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Posted 09 January 2021 - 11:52 PM

I am NOT an expert, just a driveway DIYer but with the same car as you and with all the same problems I consulted this forum (and others) and came to the conclusion that, in the case of VW water coolant temperature control, OEM is best.  It is all to do with the fine temperature limits of this engine and the quality of the components needed to achieve it.  Cheaper, aftermarket components just do not cut it.  A cheaper (read weaker) spring in the stat for example will open too early and cause the coolant temperature to run cool.

 

With this in mind, I bit the bullet and went to the main dealers from the start.  That was three years ago.  Since then a perfectly working system.

 

In my humble experience - go OEM for both the temp sensor and thermostat.

 

To be fair it was only a couple of quid more than aftermarket products but well worth it.

 

Good luck.



#6 ttg4l

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Posted 10 January 2021 - 05:06 PM

A cheaper (read weaker) spring in the stat for example will open too early and cause the coolant temperature to run cool.


Agreed on this, the febi part I got, although not VW stamped, weighed double what a thermostat from ECP weighed, and I've got a lot more confidence in it lasting a lot longer than the ECP part did.

With the temp sensor, although not many physical differences can be noticed, I wouldn't ever go back to using an aftermarket one. The coolant leaked into the loom and caused me a nightmare trying to find a short that was blowing fuses. Luckily the only thing I lost through this was my oil level sensor and associated wiring, but had I left it any longer and had the coolant gone any further, then I could've needed a new instrument cluster and the loom for the fuel sender (they share a ground which was affected by the coolant migration).

#7 TGDTDI

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Posted 10 January 2021 - 06:08 PM

Among my friends ,family,neighbours and myself i have come across at least 8 VAG 1.9 tdi's with low running temp on the dash.

All of them was fixed by fitting a new stat,never bought genuine.

Febi,Meyle,Delphi and others have been used,some of them with over 5 years use now without any issues.

Not saying that all aftermarket is good,i always stick to well known oem supplier brands.







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