Thermostat packing in

[DavGTI]

Hi guys, after the freezing cold weather we’ve been be having reaching minus 7 where I am my thermostat seems to be beginning to pack in. Car heats up to 90 as it should in approximately 3 miles or so and will continue to stay at 90.

However I noticed 2 days ago I was letting the car roll down a hill approx 1/4 mile long in 5 gear with minimal acceleration and noticed the gauge was reading about 2 or 3 bars off 90 then as soon as I start to accelerate again it goes back up. I’m assuming this is the beginning of the end for my thermostat lol and will be looking to get it replaced as soon as possible.

My question is purely just out of curiosity and want to know how this happens? My understanding is that the thermostat opens to allow coolant flow and closes to reduce it, is this correct? And assuming I’m correct, if so how come when the car is rolling down the hill the thermostat will stick open for a while causing the temp to drop then when under acceleration will it begin to close again allowing the engine to heat up correctly?

Apologies in advance if this question is a bit daft or I’m looking at this wrong, curiosity is getting the better of me lol

Thanks.

[Dannyboi#722]

Hi guys, after the freezing cold weather we’ve been be having reaching minus 7 where I am my thermostat seems to be beginning to pack in. Car heats up to 90 as it should in approximately 3 miles or so and will continue to stay at 90.

However I noticed 2 days ago I was letting the car roll down a hill approx 1/4 mile long in 5 gear with minimal acceleration and noticed the gauge was reading about 2 or 3 bars off 90 then as soon as I start to accelerate again it goes back up. I’m assuming this is the beginning of the end for my thermostat lol and will be looking to get it replaced as soon as possible.

My question is purely just out of curiosity and want to know how this happens? My understanding is that the thermostat opens to allow coolant flow and closes to reduce it, is this correct? And assuming I’m correct, if so how come when the car is rolling down the hill the thermostat will stick open for a while causing the temp to drop then when under acceleration will it begin to close again allowing the engine to heat up correctly?

Apologies in advance if this question is a bit daft or I’m looking at this wrong, curiosity is getting the better of me lol

Thanks.

Hi there, my edition 30 (dsg) was doing this also when driving on a motorway. Would be at 90 then would drop 2 bars just like your, so decided to changed the main thermostat. Since this haven’t had anymore problems, fingers crossed!!! Is your car a manual or dsg? manual as two & dsg have three.


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[DavGTI]

Hi mate, my car is manual. Yeah I’ll be looking at getting the thermostat changed some point this week or next if possible. I’ve read a few others on here saying same thing that temp was dropping on a motorway run. I took mine a run down the motor way and it stayed at 90 no bother seems to be only when I’m rolling down a hill while I’m gear and foot completely off the accelerator. If I ally any acceleration at all it will climb up again to 90.

I’ve possibly just caught it at the right time before it begins to get worse lol

[19TW80]

Mine packed up recently after I noticed temp was dropping a couple of bars on my A3 London-South Coast run, and got it replaced a couple of weeks ago. There was a mix up with the part i.e. the thermostat was ordered, rather than the thermostat and the housing, which meant a few extra days without the car. Anyhow, car actually feels as though it's driving better now, and MPG has also improved. Am I right in saying that the car would have been running rich, as it was continually trying to get the engine up to the correct temperature? MOT next week - fingers crossed!

[DavGTI]

Bit of an update on this. Took the car out yesterday and on a long downhill run on the motorway from glengormly to Belfast I let the car free wheel In gear again to see if it would start to drop and to my surprise nothing. Car has stayed at a full solid 90 degrees. So decided to put this to the test drove up some back roads and to where I know a longer downhill run and let the car free wheel in 5th gear again as I had done before and once again nothing car is at 90 degrees and not dropping temp at all. Very strange  could of possibly been the minus 7 temperatures during last week that cause this. However I’m not convinced cars booked in on 6th Jan for a service and thermostat replacement and get the oil pick up pipe done as well as it’s just hit 80k.

[Ads22]

Mines been doing this too lately, on longer motorway / A road runs it sometimes drops to 75 and then back to 90. Think my coolant level may be slightly over full but not sure to be concerned or not. Its been better in slightly warmer tempuratures.

[DavGTI]

I don’t think these cars seem to like the cold weather very much  . Mines hasn’t dropped at all since I made my initial post lol. Although the weather at the minute where I am is 11 degrees today and the other week it was minus 7 lol so a big difference there. As I said before I will be changing it anyway as good measure as car is due service next month anyway so I may as well get it all done.