Changed Thermostat, now car overheats.

[jbrickbm]

I bought my mk3 gti 2.0 last october. Ever since i bought it the engine has never ran hot, the temp gauge has always stayed really low, or at best after the car has been running for a while and sitting idle maybe at a 1/4 of the way up, and my heat has barely worked, maybe running warm a little bit when the car showed 1/4 of the way on the gauge.

I've been thinking that it is probably a thermostat problem, I purchased a tstat and some coolant and following Dan's DIY tstat change I put the new thermostat into the engine block then put the oring in, then the thermostat housing over it. It seems like I finally have filled the coolant up and the car warms up like normal it seems like, but the gauge keeps going up to 230f and thats when i turn the engine off. The top radiator hose gets hot, the bottom radiator hose and radiator are cold.

I dont think it could be the water pump because I didnt have any issues before with overheating, but when I take the hose off of the top of the coolant bottle and rev the car up nothing comes out. I saw in another forum of someone recomending sucking on the end of the hose to pull coolant through? Does that make sense? Could the thermostat i put in be bad? Is it possible to put the thermostat or o-ring in the wrong even if tstat is facing the right direction? Please any help would be appreciated. thanks

[jay86]

You have an air pocket. Drain the coolant and fill the radiator. You will need to also fill the block.

[jbrickbm]

You have an air pocket. Drain the coolant and fill the radiator. You will need to also fill the block.

Drain the coolant from the bottom radiator hose? Do you think the air pocket is in my radiator? Whats the best way to fill the coolant into the block? Any details would be appreciated, I am gunna go out there tonight after work and work on this. Thanks.

[Anony00GT]

You have an air pocket most likely, but no need to go crazy draining. Try this:

1. Let the car idle with the coolant cap off until it's hot. It helps a little if you jack up the side of the car where the coolant bottle is, but that's not necessary.

2. Shut the car off, let it cool down. Keep the cap off.

3. Top off coolant, and repeat step 1

4. Install the cap and take the car for a spirited drive. Make sure you've got good heat, temp gauge should stay in the middle, and all air should be purged by this time.

If coolant overflows from the bottle during this process, that's normal. It's air coming out, pushing coolant out with it. Top off as necessary throughout the process.

[jbrickbm]

I've done the idle thing with the cap off, I've read in other threads that that just sucks more air in if the coolant bottle starts spewing coolant.

[jbrickbm]

After running the car for 15 m now, the top radiator hoses are hot and the bottom one coming out of radiator is still cold. The little hose coming out of the side of the block when I unhook it from my coolant bottle nothing is coming out of it , I've read that there should be a steady stream, if not air coming out, but the hose has nothing coming out.

[Anony00GT]

It won't suck air back in when it burps, that's air coming out. Once it burps, add coolant to the full line again.

Alternatively, fill it up, go for a spirited drive with the heat on, check the level, top it off, repeat as many times as necessary. This works sometimes too.

It's a pain to purge all the air out of this particular system. VW didn't give us any bleeders to work with.

[jbrickbm]

I'm really starting to think its my thermostat, maybe I put a bad one in. I just went out there and drove the car around until temp got to 215 , parked it, now its cooling and I've opned the viola.t res. Again the radiator is cold and the lower hose is cold as well.

[Anony00GT]

It's possible, but not likely. I haven't seen too many thermostats bad out of the box, even cheap ones.

It's easy enough to change, if you're unsure, get a good Wahler stat and swap it in.

[jbrickbm]

After this morning, of running, topping it off, I actually parked my car on an inclinefront facing down, and massaging more hoses. I decided to drive it to work 20 mi, and stop when needed to let the car cool down. To my amazment the car never overheated and when I got to work the lower radiator hose was hot, so I think its fixed, thanks for everyone's input and help!

[Taran]

if you're unsure, get a good Wahler stat and swap it in.

X2 on the Wahler brand name for thermostats

Something about the other brand thermostats not extending far enough when cold to block off coolant flow (AKA do its job) to the radiator causing delayed warmups.

Also, the repair is not complete until you check your electric cooling fan(s). Go for a drive and let the car idle until the cooling fan(s) come on or it overheats.

If it overheats, fix the fan(s). If the fan(s) cycle on and off, the repair is complete.

[Anony00GT]

After this morning, of running, topping it off, I actually parked my car on an inclinefront facing down, and massaging more hoses. I decided to drive it to work 20 mi, and stop when needed to let the car cool down. To my amazment the car never overheated and when I got to work the lower radiator hose was hot, so I think its fixed, thanks for everyone's input and help!

Sounds like you're good to go

X2 on the Wahler brand name for thermostats

Something about the other brand thermostats not extending far enough when cold to block off coolant flow (AKA do its job) to the radiator causing delayed warmups.

Also, the repair is not complete until you check your electric cooling fan(s). Go for a drive and let the car idle until the cooling fan(s) come on or it overheats.

If it overheats, fix the fan(s). If the fan(s) cycle on and off, the repair is complete.

Yes and no. The cooling fan switch is in the radiator, if there's an air pocket, the fans won't come on but the gauge will still indicate overheat. It takes some experience to know the difference between air pocket and true overheat.