MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: R88TTD on November 29, 2024, 12:29:34 pm

Title: Temp gauge dropping when heaters on
Post by: R88TTD on November 29, 2024, 12:29:34 pm

Hi guys

I started experiencing new problems with MK5 gti
The temperature gauge drops from 90 to 75 then 50 gradually as soon as I turn my heaters on

Now the heaters are blowing hot air as normal
I asked about and some tell me the battery , some tell me the temp sensor and some are telling me the thermostat, water pump was changed about 15k miles ago so that ruled out

No head gasket issues , no over heating

Just wondering if anyone had this issue before Thanks

Title: Re: Temp gauge dropping when heaters on
Post by: ZoliWorks on November 29, 2024, 03:55:04 pm

If you want to find out if it's the thermostat or not, go on the highway, drive at a constant 130-140kph without the heater and see if the temp drops. If it does, it's the thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: Octoparrot on November 29, 2024, 04:39:27 pm

I'd put my money on the thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: mjmallia on November 29, 2024, 06:18:03 pm

Thermostat for sure

Title: Re: Temp gauge dropping when heaters on
Post by: Mk5gti on August 28, 2025, 01:59:32 am

Hi, did you ever resolve this issue and what was it?

Title: Re: Temp gauge dropping when heaters on
Post by: crookedd on August 28, 2025, 08:08:09 am

I had the same issue years ago. Also car never reaching 90 degrees fully in winter or dropping from 90 when constant highway speeds. Issue was thermostat.

Title: Re: Temp gauge dropping when heaters on
Post by: Mk5gti on August 28, 2025, 08:12:16 am

So my issue is the needle drops when I turn heaters on
Both thermostats have been done and temp sensors using genuine parts, while driving the needle doesn’t drop, the needle will only drop at idle with heaters on

Title: Re: Temp gauge dropping when heaters on
Post by: matius344 on December 03, 2025, 11:54:36 am

Quote from: Mk5gti on August 28, 2025, 08:12:16 am

So my issue is the needle drops when I turn heaters on
Both thermostats have been done and temp sensors using genuine parts, while driving the needle doesn’t drop, the needle will only drop at idle with heaters on

I got the same issue.

Anyone ? Oher ideas than Thermostat or temp sensor ?