Coolant temp takes for ever to warm up and drops while driving...

Shift518 Automotive
1

I am sure as soon as you read the title you though thermostat stuck open.

I got the Jetta back out becasue my beater died and I need to drive something. I put it away around dec and it ran fine. It warmed up and stayed steady at 190 just like it should. When I built it I never connected the heater core hoses for coolant, to tidey up the engine bay and in the summer time I dont need heat. But now that I need to drive it when its cold out I rigged up some heater core hoses. I jacked the drivers side way the hell up in the air, thats the side where I installed the filler neck (highest part of the system) and filled it up. Warmed it up shut it off and topped it off again, repeated process a few times that night and went to sleep, cap off still jacked up in the air. At this time there was NO heat coming out when it got up to temp. I figured there was still a ton of air in the system. Next morning I went out and added alot more to top it off, so I know a ton of air came out overnight. Fired it back up and instantly started getting heat and it got up to temp fine and had great heat. Shut it off cooled it down, topped it off a little more and went for a ride. It took for ever to get up to temp. Once it did I drove around and it would drop temp like a stone… to the point that it was back to almost dead nuts cold as per the shit gauge on the cluster. VAG showed like 85C at that point. If it sits it would get back up to temp. CEL isnt on but it has a code for temp out of range or improper flow or somthing like that I cant remember ill check when I get home.

I already replaced the temp sensor with a green top, and I still have an extra one I can try too. The T-Stat was working just fine 2 months ago when I parked it, so how the hell can it all of a sudden stick open?

The t-stat on these cars are a bitch to get to and that means I have to empty the coolant again, and bleed it again…

Do you think there is just a ton of air still in the system?

2

put a piece of cardboard over the radiator, done.

3

Sounds like a Tstat.

Just had a similar issue with my Subaru.

4

That was the first thing out of my mouth last night durring the test ride too! lol

Yeah I ordered one and will suck it up and toss it in. It has to be the 5th time I drained the coolant from this build to mix/mod coolant relaited stuff.

5

Blame the noobie mechanic for this one… When I put the motor back together, I put the oring in the block, then the thermostat then the plastic radiator flange on… I read the bently this time and saw that it goes block-thermostat-oring-flange. So I assume that the flang on the thermostat didnt seal well against the plastic rad. hose flange and just allways blew by. OR the orentation of the thermostat in the car was wronge. They say that your suposed to place the thermostat in the block clocked so that the support pridge piece on the thermostat is vertical, and it wasnt. But that I dont get becasue it physically fits in there the no mater what way is sits, and I dont see how the cyclinder will work differently with it clocked different ways.

who knows, I put a new one in anyway, the correct way and it works like a champ.

Runs perfectly now, backed the boost off to 16psi and I am around 16.5deg timing and it pulls great, still way more than anyone needs for a daily let alone the cold weather duty it will have to do for the next few months but I am happy with it.

6

Good to hear!

7

turn it up to 26psi.

8

It was at 24 when i put it away in dec. With only 14deg timing in it and a sketchy ass alignment it was scarrry.

I gota keep it down and easy until spring. then I will really get to tuning it and cranking it up.