Temperature Gauge 3/4 then back to 2/4?

[Schwebe]

Hello, just today I was driving my car a bit spirited and noticed that my temp gauge went to the 3rd dash, soon after my coolant temp light came on, within 30 seconds the gauge went back down to half? I am not sure what would cause this, my coolant reservoir is just a bit under minimum. I replicated the issue on my way home and the exact thing happened. It does not go past the 3rd dash and goes right back down to half...

I have also started to notice that when it was cold out it took forever for my car to blow hot air, it was like I had the A/C on! It just started to do that towards the end of the winter, before it was nice and warm. I have to take my car for a 3 hour trip this weekend so I would like to figure this out ASAP. Thanks!

Also forgot to mention that I just had my timing belt and service done about 3k ago, they flushed my coolant as well.

[Charles.waite]

Bad water pump maybe. Or a bad thermostat. Given the lack of heat my guess is thermostat. How long does your car usually take to warm up to the middle of the gauge?

[Schwebe]

Well I would hope my pump is okay! Has less than 3k on it. Anyway to test the thermostat on these? My car probably takes 10 minutes to warm up? Could be wrong, don't pay too much attention there! I was assuming my thermostat was opening too slow causing this or something?

[Charles.waite]

Normal warmup time should be 5 minutes or driving or less (not sitting idling). Sounds like your thermostat is shot which is really common.

[Schwebe]

Hard job on these engines?

[Charles.waite]

Hard job on these engines?

Really not too bad. 2 hour job tops.

[Schwebe]

Update, replaced the thermostat and flushed coolant, drove it for a week with no issue at all. I couldn't get it to overheat. Then today I drove 30 seconds to walmart and back and it did it again?!

[Schwebe]

After a bit more testing I have more information and hopefully I can have more input. So my car takes about 5 minutes to heat up and then start going over 96 degrees Celsius. The temps climb up till about 120 degrees. My fans are going crazy so I know they are running. I went out to my car a bit ago to do a vag com scan and it pulled no DTC's. When I started the car up the idle was horrible! I didn't even think it was going to stay running. I still do not have heat. Could a plugged heater core cause the car to overheat? I didn't think that was possible. Also my water pump only has a few thousand miles on it. How likely is it that it is bad?

[Johann2.7t]

My 03 1.8t has done the same thing a few times. Very scary.

First couple times was right after a full timing belt job with thermostat and pump. Figured there was just a bubble. Second time was after replacing my J pipe and electronic thermostat. This time I used a coolant vacuum pump to pressure test the system and refill the system. I feel pretty confident its bled perfectly so I don't suspect it's a bubble.

Third and final time was yesterday about 8k after all of that work.

I will add my car doesn't leak or loose any coolant. The heat isn't amazing either for what it's worth. Coolant gauge heats up quickly and stays centered apart from these times.

My .02!


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[WB650]

Fan running on cold start immediately?

Maybe coolant temp sensor needs replacing

[B6A4Dave]

G62 in the rear flange could be going wonky.

[Schwebe]

Hello everyone! Back for the update, I took my car back to where I had my timing service done to have them look at it. The owner took the water pump out to make sure it was still fine, that was all good. He replaced my coolant temp sensor and bled the system and also flushed my heater core. I know these cores are not really flush able but he pumped a solution through it for 4 hours and it seemed to clean it out. He had it for two days and could not get it to overheat. So I picked it up and drove it home, on my way home I was beating on it to try to get it hot and it refused. I thought it was fixed. On my way home my oil pressure light came on for the first time ever. It has been randomly coming on the past few days when low rpms? Anyway, it remained cool for a day or two and then today it overheated. I am so frustrated with this, I am back to no heat and over heating...what am I missing here!

[Schwebe]

Also took it to a local shop and asked if they could do a pressure test for me, I am 3 hours from home (at college) and can't do anything myself. They ended up doing a chemical test and saying it failed and suspected a crack in the block but I don't think they knew what they were talking about. What about my headgasket? Or am I looking a cracked head.

[WB650]

1.8 or 3.0?

[Schwebe]

1.8t

[rocket1420]

Is there coolant in the oil?

[BISHILVR]

Head gasket, pushing air into the cooling system.

[Schwebe]

Coolant and oil do not appear to be mixing. That'd make sense if it was pushing air into the system because it was fine for a bit and then got bubbles in the system.

[Johann2.7t]

Head gasket, pushing air into the cooling system.

doesnt explain low cabin heat

[Charles.waite]

Have you checked that the water pump is working properly? Sounds like a busted pump. That or the Heater core is really blocked and isn't working

[Schwebe]

Yeah like I said the water pump was just pulled out and verified working the other day, also heater core was flushed with a solution for 4 hours. If the head gasket is putting air into the system that would explain bubbles forming in the heater core causing no heat?

[old guy]

Yeah like I said the water pump was just pulled out and verified working the other day, also heater core was flushed with a solution for 4 hours. If the head gasket is putting air into the system that would explain bubbles forming in the heater core causing no heat?

Yes that would explain the loss of heat. Any time you get air in the heater core circuit it will greatly diminish the flow through the core and thus you will experience reduced heat in the cabin. Here's an explaination of what happens when you get air in the heater core circuit: Clicky click®

[Schwebe]

So I should just keep bleeding it through that heater core bleed hole in the hose? Anyway to confirm its headgasket since oil and coolant are separate.

[old guy]

So I should just keep bleeding it through that heater core bleed hole in the hose? Anyway to confirm its headgasket since oil and coolant are separate.

A blown head gasket doesn't always cause the oil and coolant to mix. It depends upon where the gasket is compromised. Probably the easiest way is to check for combustion gasses in the coolant.

[Schwebe]

The shop that I took it to said it did fail the chemical test due to combustion gasses in the coolant but they said it was a crack in the block and not the headgasket, they seemed pretty shady so I didn't trust them.

[Charles.waite]

Or blocks are pretty sturdy. I've never heard of a block cracking without catastrophic damage being the result, aka you snap a rod and it blows through the block.

I would bet the head gasket failed given the info and symptoms you've got

[Schwebe]

Like I said before I am at a college that is 3 hours away from home so I can not do this job myself...fair prices for a shop?