2003 TDI: Running too cool...

Hello all. I recently purchased a 2003 TDI Beetle with 5 speed. The check engine light was already on. I bought from blueboy / lightflyer1 on this forum. He well documented the history of the car as well as the thousands of dollars he spent.

Just a quick baseline summary: the car engine had the head rebuilt. It has a Malone Stage 2 tune. It has had a ton of other improvements and upgrades as well. http://forums.tdiclub.com/showthread.php?t=448086

He was forthcoming with the issue and even gave me a new temp sensor, new thermostat, and thermostat housing. I replaced yesterday but I’m still getting a CEL. After hooking a diagnostic computer to it, I’m at 172 degrees Fahrenheit after ten minutes of idle. The thermostat, old and new open at 188. The thermostat, thermostat housing, and green and brass sensor looked fine. I’m certain they were replaced before blueboy / lightflyer1 had it.

The only other diag faults are glow plugs 1-3 are showing up. So, bottom line, the new thermostat isn’t opening because the car isn’t getting to the prescribed 188.... at least it’s not under an extended idle. And based off of that, it’s throwing a CEL.

Any guesses, ideas, suggestions out there? Thanks!
Daniel

Needs to be driven to build any heat. Diesels don't make excess heat unless they are under a load. And if it has no EGR cooler, or has no EGR commanded at all even if the cooler is in place, it will be even worse to build heat.

The MIL is on sounds like due to a fault in the glow system.

The car was well driven on a 35 mile commute every day while I had it. The glow plug codes are a known issue and should only require cleaning of the harness, more than likely. They were all replaced when runonbeer did the engine/head. IIRC the egr was not removed but the stage 2 Malone tune may have it turned off. It never caused an issue for the approx 2 years I owned it. I also gave the OP the Flashzilla tuner box so if it was an issue reverting it back to stock tune may help. I don't think that is the issue though. Was the sensor replaced as well or only the thermostat? I also took it to the dealer (runonbeer has moved) and they diagnosed it as the thermostat/sensor as well.

10 or even 20 minutes at idle doesn't mean much especially/depending if any cabin blower fan speed was involved. Get it out warm it up and run it at 60+ mph for 15 minutes and report back what the coolant temp is. Leave the cabin blower fan at a minimal setting.

Lightflyer1 said:

The car was well driven on a 35 mile commute every day while I had it. The glow plug codes are a known issue and should only require cleaning of the harness, more than likely. They were all replaced when runonbeer did the engine/head. IIRC the egr was not removed but the stage 2 Malone tune may have it turned off. It never caused an issue for the approx 2 years I owned it. I also gave the OP the Flashzilla tuner box so if it was an issue reverting it back to stock tune may help. I don't think that is the issue though. Was the sensor replaced as well or only the thermostat? I also took it to the dealer (runonbeer has moved) and they diagnosed it as the thermostat/sensor as well.

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I replaced the sensor as well. The old one was green and brass suggesting being replaced vs the oem black sensor.

Did you reset the codes after the repair? Autozone has a generic code reader that may work if you don't have one, to reset them.

I did reset. CEL came back after I cleared them. I’m going to run her down the road at highway speeds while my buddy monitors the data.
I might do the run on both oem and Stage 2 settings. I’ll report back when I get a chance to do this.

You've got a Stage 2 tune, get out and put your foot in it (to heat it up)!

Out of curiosity, are your fans running (when you really don't want them- engine is cold)?

GPs- I'd found an instance in which the connector on the inside of the harness was weak, in which case I stuffed come foil on the GP and then shoved the connector down. Solved the problem: GPs had checked out; harness voltages checked out; only thing left was the connector (I'd previously cleaned it).

(on my '03, I'm on my second replacement glow plug harness, as the plastic boots of the first one were already cracked and degrading and causing codes - so do give the harness a close look).

Something we found out a long time ago... just because a thermostat is new, does not mean it works right. We test every thermostat before installing or selling them. We average a 10% reject rate... we send them back. So, maybe the next guy gets our 'low temp' thermostat!

We do not like a thermostat that starts opening at 175f degrees. We also do not like them still being closed at 190. It does happen, but more open too soon than late.

To test thermostats, we put the thermostat into a pan and heat it up to boiling. We use a candy thermometer or a digital thermometer that will measure up to 240 degrees. Watch the temp for when the thermostat cracks and when it is wide-open. Then, cool it down and watch when it closes. We see too many that close at 170-175 degrees, which means you will be getting poor fuel economy. Overheat warps heads. We would rather too cold than too hot, but right is right.

Hey Frank,
Have you ever run in to issues installing used inlet/ thermostat housings with broken locating tabs for the stat?
Besides that, how are you doing?

One of the guys at Kirk's said I got lucky because Donna's car heats right up even in the winter. Didn't think so at the time, but he may have been right. My Jetta is a fight to get up to operating temp. I tested 3 stats and they all act different from opening/ closing times and amount they open.

Franko6 said:

Something we found out a long time ago... just because a thermostat is new, does not mean it works right. We test every thermostat before installing or selling them. We average a 10% reject rate... we send them back. So, maybe the next guy gets our 'low temp' thermostat!

We do not like a thermostat that starts opening at 175f degrees. We also do not like them still being closed at 190. It does happen, but more open too soon than late.

To test thermostats, we put the thermostat into a pan and heat it up to boiling. We use a candy thermometer or a digital thermometer that will measure up to 240 degrees. Watch the temp for when the thermostat cracks and when it is wide-open. Then, cool it down and watch when it closes. We see too many that close at 170-175 degrees, which means you will be getting poor fuel economy. Overheat warps heads. We would rather too cold than too hot, but right is right.

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Add to that - It's also too cold in Winter !

Thermostat definitely the place to begin diagnosis.

Now if you could only get me one of those "guaranteed thermostats"
and come over and install it !

My cooling fans never comes on (except with AC), replaced switch,
and probably got one of those 10% reject thermostats.

Haven't tested one in decades ! Thanks for the advice.

And I sure wish I had a temp gauge (still plan on adding someday)

Hi Jim,

Except for trying to kill myself on Kirk's ATV, things are great! That was an expensive trip 9 weeks ago...

Last week, I drug the Hurco CNC home and got it placed and it's wired up, ready for new monitor and keyboard. It's set up to port ALH and AHU's. More to come. CNC machine's can be fun.

As for the thermostat housings, I think most of the time the holding tabs break off of the thermostat housing, making installation a bit of a pain. The o-ring usually sticks harder than the holding tabs can stand. I don't have much problem replacing a part that costs $5.

I ended up trying wire holding the thermostat in and folded the ends over and it held perfectly(I WILL FIND OUT TODAY).
Good to hear your moving forward Frank. That machine sounds like the cats **s. Good tip on checking stats closing temps.
My new one cracked open at (don't have my notes so going by memory) about 194, fully open at 209, started to close at 201, closed completely at 184. I am guessing it will run at 201 t0 204, and that would be great.
Old one (again, by memory. Long term better than short term. That's why I take notes, just don't know where the **ck I put them!) cracked open around 183, fully shortly over 200, stayed FULLY open well below 200, and was still cracked when I pulled it out and threw it away at 167.
Digital therm and slowing the flame down to raise temps slowly make a diff. I will find out today, I am guessing it will work fine. Engine would fall on it's face under hard acceleration and smoke. Way too cool.

I use OEM thermostats. I don't think I've across a bad one, but they are more money.

Also I found you can use thermostat housing with the tabs broken off. I use a rubber band attached the T-stat, run in through the front and put a stick through the rubber band to hold it in place. When you get it tighten just cut the rubber band and pull it through.

A housing is pretty cheap though.

Joe, that's a good trick. If I have a housing that looks like it won't crack before 50k, I'll try that.

As for thermostats, if they are 90% good, it might take you a while to find a bad one. We go through a bunch of them, as we are the ones that say,"Just because your temp gauge says 190 doesn't mean it IS 190...". So, we replace a lot of thermostats. And most of them are OEM. Eventually, even a 'good one' goes bad.

Honestly, with relatively new common rails, we saw plenty that were overheating. Of course, the temp gauge said everything was ok. I wonder why they have to make a different thermostat. They do the same exact thing...