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Discussion Starter · #1 ·
Hello everyone, Been a while since I posted, Guess i have to consider myself lucky. :wink2:
I have a 98 beetle that I have done about everything under the sun to. I only paid $400.00 for it so......
I have pulled engine and replaced a bunch of gaskets, valve cover , exhaust, rear main seal, front trans seal (auto-01m), while out did the water pump, timing belt and tensioner, all new brakes, wheel bearings, tie rod ends and the list goes on.

Anyway, I got another 99 beetle also 2.0 auto and did all the same stuff to it only I did not pull the engine as the rear main seal was not leaking. Been running it for about 8 months and it has been fine. I noticed once while running it on a cold morning with no warm up time, the blue temp light took longer to go out than normal. I figured it was just colder outside. I also noticed that the heat from the vents was not as warm as i thought it should be. didn't think much more of it.
A little ways down the road the Blue light returned and less heat from the dash. It stayed that way till I got home. let it set in driveway and idle to see if it would warm back up and it did and the blue light went out.
The wife took it to work this morning and it did fine on the way in but on the return trip she called about halfway home and said the check engine light came on and the blue temp light came on and heat from dash was cool. I told her to come on home as it would be fine. I got in the car after it had sat for a couple hours and noticed the defroster was on and I know this turns on both the cooling fans. Did a scan on it and it says the engine coolant temp too low.
I have replaced:
water pump, timing belt, tensioner, thermostat, several hoses, drained system and filled with new 50/50 G12.
Think my new thermostat is bad?
 

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5/23/10 <3
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Discussion Starter · #3 ·
Yes replaced the sensor, Even if sensor were bad that would not affect the temp of the air from the vents I don't believe. It should remain warm regardless I would think. Do these cars have a sensor that tells the ambient temp to the computer? Is it the little sensor under the cowl cover close to the wipers? If it does, does it tell the fans to remain off when ambient temps are below a certain degree even though the defrost is switched on?
I am going to run it tomorrow to see what happens.
I need to read more Bentley i guess.
 

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Discussion Starter · #5 ·
It does not overheat, it is the exact opposite. I just replaced the pump about 800 miles ago.
 

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Sounds like a bad t-stat. On my wife's '03 Beetle 2.0 vert we had the same problem. OEM t-stat cured it. The ecm needs to see full operating temps within 6 minutes or so. If it falls outside that window it will set a check engine light. With the defrost on it will run the cooling fans because the A/C is also running at the same time. The fans will cool off the coolant to much if the t-stat is lazy to close off as needed to keep the engine temps up.
 

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stat

If the previous owner mixed the wrong coolant in the system it will create sludge and the thermostat will get stuck open and will cause the temperature incorrect readings. seen it happened before.
 

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Discussion Starter · #8 ·
When I drained the coolant to do the water pump and timing belt it looked really good. No signs of being mixed. I am thinking I will have to get an OEM t-stat.
Thanks.
 

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It does not overheat, it is the exact opposite. I just replaced the pump about 800 miles ago.
Try a thermostat first but it might be your water pump if you didn't replace it with a OEM Volkswagen with metal fins.
Last year when I bought my Beetle it was really cold out, didn't see temps above 4 degrees for almost a month straight. My blue temp light stayed on forever and I didn't have heat. Popped the water pump out when doing the timing belt to discover that the pump had no fins at all left. I didn't know at the time the OEM pump was metal and the aftermarket was plastic. I end up replacing it with a aftermarket but because their was a few reminates of the old pump still in the system I couldn't get out it destroyed my new one in a matter of a few hundred miles. I got it cleaned out as best as I could and now have a OEM pump. I have put right around 15,000 miles on it since then and I have very hot heat in my car now. Yesterday it was about 3 degrees and my co-worker asked if he could crack the sunroof to let some fresh air in! When the cooling system is working well, these little cars are like a furnace! Good luck with your car, hopefully you find your problem quickly. Its wayyyyyy to cold to not have heat!!!
 

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You can check your water pump while the t-stat is out. The fins on the pump are right above the t-stat opening and you can feel them to see if there OK.
 

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Discussion Starter · #11 ·
I'm going to try a thermostat. I replaced the pump with one that has the metal impeller when I did the timing belt and tensioner.
 

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I had the exact same symptoms on my wifes 99. Hooked up my OBD tool and to my phone and monitored my temps stayed constant around 130degree. Popped in a new t-stat and now it's a constant 203-205 all day long
 

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I don't get all these failed t-stat claims in beetles. They are the same exact design as most t-stats and see no reason for a higher failure rate than most other than possibly sludge. Yours however sounds like a stuck open t-stat. The coolant starts flowing through the radiator as soon as you crank it with no regulation to flow at all and as cool as it has been I can easily see the engine never getting up to operating temp. You could always pinch off the lower radiator hose off and that would verify if you have an open flow problem if the engine heats up normally.
 
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