coolant temps help/advice

[sambb]

Its been pretty cold driving home at night in Sydney lately eg 5-8 degree nights, and I've noticed that if I get the heater on as soon as hot air will come out, that the cluster engine temp gauge wont make it to 90 degrees. It'll park itself on 70.If I turn the heater off again the temp will get up to its normal zone though. Throughout this the car is in 4th and 5th gear cruising.
I didn't think much of it as it was very cold, but this afternoon I decided to have a look in VCDS on the way to work. It was 12-15 degrees (so warmer) and there was a fair bit of traffic to keep the temps up. The VCDS temps at normal operating temps agreed with the cluster gauge so I think that gives the coolant temp sensor a clean bill of health. But sure enough if I was at normal operating temp on the cluster (90 degrees), if I put the heater on full heat/speed the VCDS temp went from 90 degrees down to 68 degrees! and the needle nearly got down to the 50 degree mark on the cluster.

SO .... is that normal? I've only had this car for one winter and was building the thing throughout and I cant actually remember how it behaved in the cold last year. Surely the heater wouldn't have that big an effect. I'm thinking the thermostat is suck open. thoughts......

[h100vw]

Sounds like the stat.

[sambb]

Do you always do a housing with a new thermostat? I have the o-ring already.

[Umai Naa!!]

If it's a plastic housing, yes. They tend to warp and go brittle over time.

[rgvlee]

I've recently done my thermo.
Symptoms were it would take ages to get to 90 indicated. On cold mornings would fluctuate and come back to do around 60.
OBD11 showed that 90 indicated can be anything from mid 60s onwards I think, can't remember specifically now. So the gauge has a fair bit of damping.
Changed the thermo and all sorted.
I replaced the housing with a metal ECS unit which was about $40 on the advice that the plastic housing is **** and I like wasting my money on shiny.
Good time to the intake spacer as taking the intake off is one way of getting access to the thermo.
The above comment about warping is probably very true, I had a very slow coolant leak (had to top up overflow every 5k) that I could never find, since doing the thermo housing I haven't had the warning come up and I am at 7k since service now. Probably tempting fate.

[simon k]

interesting... I hadn't thought about it much, but it takes a looong time for mine to come up to temperature...

replacing with a metal housing sounds like a good idea, the thermostat housing on my Focus fell to bits - basically just crumbled into dust

is this the housing?

ECS - 006660ECS01 - Heavy Duty Cast Aluminum Thermostat Housing

[rgvlee]

is this the housing?
ECS - 006660ECS01 - Heavy Duty Cast Aluminum Thermostat Housing

Yeah that looks like it. Mk iv golf fitment fits our cars.

[Sydneykid]

Possible an air lock, I'd try bleeding the system.

Cheers
Gary

[sambb]

Cool thanks for all the advice. I have a hillclimb on Sunday so not enough time to get an alloy housing although if less pressed for time I probably would have, The VW housing is 18 bucks, but they want 60 bucks!!! for the thermostat!!! jeez. Bursons carry a replacement Tridon TT1-190 (88 degrees) for stuff all so I'll grab that one. They also do a high flow version TT2000-190 and both designs at every cracking temp from 160(71 degrees) all the way up to standard.

In transverse 1.8T cars you don't have to remove the alternator do you - you can get in there with a 1/4in swivel drive can't you?

[rgvlee]

Yeah the genuine vw thermo is expensive. I got caught needing it on short notice so sucked it up.

Good luck trying to do it without removing something.

Can be done with alternator in place - but you'd need to remove the intake. I only did the latter as I was installing the ie spacer so had it all off anyway.