My car gets colder at an idle, and warmer while driving?

[Jcalvin1126]

Hello all,

First of all I am a proud new owner of a 99 Golf TDI, and to say i enjoy it would be an understatement. However, I purchased it at a cheaper amount with the knowledge of it needing some repairs.

The first thing I noticed while driving was the coolant temp would not go above 80 degree F. Additionally the heater would never get warm. (sucks because its colder here right now). Additionally the coolant temp would flat line from time to time so I knew that it must be time to change the temp sensor.

After a lot of heart ache to find the blue version of the temp sensor, I finally got that replaced. I also replaced the thermostat for good measure, and attempted to burp the system as well as I could. (don't worry I only used g12). After looking around the engine I also noticed that the EGR valve is basically jimmy rigged to be wide open at all times, and the cut off switch was hanging there. Additionally the breather hose to the valve cover was removed, and blocked, and the vacuum lines plugged up. ( I have my work cut out for me)

So here is my problems, after fixing a majority of those issues. Now when I drive the temp will rise to right under 190 degrees F (just under middle). However, when I slow down and idle the temp will drop to just above the 3 bars at flat line. The heat will be warmer however not hot when at 190 degrees, and cold at idle.

My thoughts are I either have a massive air bubble screwing with my temp sensor, and potentially stuck within my heater core. Or, I need to replace the water pump. I plan on doing a 100k maintenance to it as the car has 240k miles, and I don't know when the last time it was done.

Any help will be much appreciated thank you!

( I am by no means a diesel mechanic, however I was a 6 year aviation mechanic for the U.S. Coast Guard, and a Back yard Gasser mechanic since I was 16. I am no master however, I am mechanically inclined so I can do the maintenance if you guys suggest something)

 

[libound]

How cold is it where you live?

 

[Jcalvin1126]

Currently 20 degrees F

 

[Tdijarhead]

What you are experiencing now with regard to your heat gauge is normal. Diesels tend to cool at idle on cold days.

 

[Jcalvin1126]

Well, I haven't drove it yet today. Is it normal to cool down to 60-70 degrees F? It will come from 190 F to 60-70 F in less then 45 seconds. I guess I should have put that in the original post. Sorry of my ignorance on diesel, I was unaware of cooling while idle.

 

[TDI_G]

That sounds to me like a thermostat that is stuck open. Once the car is up to temp it should stay there.

 

[Jcalvin1126]

So I purchased a bad thermostat? Ugh, I hate Auto parts stores.

 

[TDI_G]

The general rule with thermostats is to get the OEM one and not a generic one from the auto parts store. Here is one here http://www.fixmyvw.com/thermostat-for-tdi-engines-alh-and-bew-044121113/ along with the housing http://www.fixmyvw.com/alh-thermostat-housing-o-ring-038121121/

 

[Jcalvin1126]

Ive never had a problem with them before, I dont buy the cheepo ones however I always get OEM specs. I dunno, I guess Ill give it another whirl. VW g13 cost is outrageous I dont care about 20 bucks for a thermo but 30 bucks for coolant is a drag.

 

[CopaMundial]

When the engine is running, is there coolant entering the reservoir?

 

[TDI_G]

If you have changed your coolant recently, just drain it into a clean container and reuse it.

 

[Tdijarhead]

Regardless of where he got his new thermostat it sounds like its working. If his temperature comes up to (almost) where it should be. My 2000 and my 05 do the same thing, my 2000 has a brand new OEM thermostat and housing with my belt change last fall. When they idle depending on ambient temperature sometimes that needle goes almost back to the cold mark. Block off some of your radiator with some cardboard, coraplast or pipe insulation, that allows the engine to come up to temp quicker and stay there longer.

CopaMundial asked the make or break question. Warm your car up and unscrew the radiator cap. Is coolant flowing from that little tiny hose coming into the backside of the resivoir bottle? The one near the top. If it is your system is probably functioning just fine.

 

[Thermo1223]

All part store thermostats are garbage. All of them unless you can verify it is indeed made by the OEM manufacturer.

I've been burned too many times.

The coolant gauge is not accurate. It is an estimation of what the ECU wants you to see. So trust me the car is never cooling down to 60-70F Maybe 110-120F at the worst. TDI's are not like a gasoline engine and hardly make any waste heat at idle.

Get a OEM thermostat even from the dealer. Drain & save the coolant, replace and be happy.

The car will burb itself automatically as long as the reservoir remains filled properly.

 

[Jcalvin1126]

Thanks for the feedback, I have not checked the flow yet, however, during my lunch break I will. My uncle once told me to do the cardboard thing. So maybe I'll do that this evening and see what happens. If those two are fine and the cardboard doesn't do the right job then I'll just swap the thermo again and give it another go.

 

[puntmeister]

Water temperatures do not quickly change. From 190F to 75F in 45 seconds?

If that is what the gauge is telling you is happening, then either the gauge is broken, a sensor is broken, or flow is disrupted (at one moment a sensor is surrounded by hot water, the next it is surrounded by air) - but neither the water temperature nor engine temperature is dropping 100+ degrees in less than a minute.

 

[copatdir6]

I can add to this discussion as I am having almost an identical situation (and I don't mean to hi-jack the thread).

My situation is, I have a 2003 Jetta TDI. Replaced the thermostat almost a year ago with another OEM one (from IDParts.com) along with the housing.

The last few weeks or so, I can start the car, drive about 15 minutes at highway speed (65mph) and the temp will hit or get near the magic 190 degree mark. If I come to a red-light or stop the needle starts to fall...sometimes as much as almost all the way back down.

Also, if I'm driving on the highway (again) for longer than 20-30 minutes with the RPM's around 2,200....the temp gauge will sometimes start to drop. Not a lot but enough but I'd say down a click or two...this seems VERY odd to me. Even though the temp has been extremely cold out here lately (around 0-10 degrees), I though once the engine was warmed up, it should be able to maintain that heat.

And I have the same issue where the air is blowing warm(ish) but not hot as it should be once the 190 mark is met.

I'm thinking the thermostat isn't the problem as it's an OEM replacement along with the housing....and I got about 10yrs out of the original one.

 

[copatdir6]

CopaMundial asked the make or break question. Warm your car up and unscrew the radiator cap. Is coolant flowing from that little tiny hose coming into the backside of the resivoir bottle? The one near the top. If it is your system is probably functioning just fine.

I'll also check the coolant....but in my experience, if the reservoir bottle is anywhere low, I get a CEL almost immediately.

 

[IndigoBlueWagon]

What the OP and copatdir6 describe is normal, at least in my experience. On my first drive of the day I go 2 miles to a freeway, 4 miles at 70 MPH, and then stop at a traffic light at the end of the off ramp. I have a winter front on the car. If it's 20F out, the car may make it to 190 according to the placebo temp gauge while on the freeway, but will usually drop a full notch on the gauge while I wait for the light to change.

Two days ago it was 0F here, I made the same drive and stopped at Starbucks. The temp gauge was about 1/2 way to normal when I stopped. It dropped almost to cold while I was in the store. This is a new OE engine with a new OE thermostat.

TDIs get great FE in part because of their thermal efficiency. But when they're not being worked hard and it's cold, they cool off. Small price to pay, IMO.

 

[Jcalvin1126]

I'll make a video of it tonight when I'm driving home from work and post it up for y'all to see

 

[Jcalvin1126]

OK so during my lunch break I turned the TDI on and let it run at idle with the cardboard in front of the radiator for about 25-30 minutes. The temp gauge did not move. Nor did I see a lot of fluid poring into the coolant tank. I felt the thermostat hose and it was warm but not hot to the touch. I also felt the coolant lines running to the water heater and they were warm not hot. The return line to the tank was warm not hot. So it feels as if there is some flow. However due to the cold weather I couldn't sit there and watch the coolant tank for long 2 minute intervals at most. I squeezed the thermo hose to make sure there wasn't a bubble there and I small fluid run to the tank so that's a plus. But does this mean my water pump is trash?

 

[Jcalvin1126]

Ahh one thing I forgot to mention earlier. After flushing the system and changing everything I let it run to burp it. At an idlenit ran the fluid through however I got the coolant light on so I added more fluid before it emptied. I drove it to work that day and while I had it idle it came on again, however I had just turned onto the highway so I gassed it to get out of traffic. As soon as I gave it rpms the light went off and stayed off. As I got to work when I slowed down the light came back on. Maybe a restricted line? Or wp is shot and is not performing well unless higher in rpm

Thoughts?

 

[IndigoBlueWagon]

These cars won't warm up by idling in cold weather. It takes a long time, hours more than minutes. And it's not unusual to have some trapped air get released in the cooling system causing a low coolant light after a flush.

Doesn't sound like anything's awry.

 

[Jcalvin1126]

Rojer that well I guess I'll just deal with it being cold then haha.

 

[joep1234]

When the thermostat is doing what it is supposed to do, it should hold the temps in the motor. If you are running the defrost, the fans are running because of the A/C is operating and will cool the radiator quicker thus cooling things down more.

 

[Smokin' Dually]

My '03 was running cool and I didn't think much of it until I researched it on here and learned that the temp gauge reads what they (VW) think you should see. I'm running an Advance mid-price (OE replacement) T-stat which (with the original housing minus the pins) fixed the problem.

I think that the big thing with the OE T-stat is that it needs to correctly block an internal port. If your replacement didn't measure up (mine did), that could be part of the problem.

Another thought, are the coolant glow plugs working? Check this out: http://forums.tdiclub.com/showthread.php?t=435144

 

[Tdijarhead]

OK so during my lunch break I turned the TDI on and let it run at idle with the cardboard in front of the radiator for about 25-30 minutes. The temp gauge did not move. Nor did I see a lot of fluid poring into the coolant tank. I felt the thermostat hose and it was warm but not hot to the touch. I also felt the coolant lines running to the water heater and they were warm not hot. The return line to the tank was warm not hot. So it feels as if there is some flow. However due to the cold weather I couldn't sit there and watch the coolant tank for long 2 minute intervals at most. I squeezed the thermo hose to make sure there wasn't a bubble there and I small fluid run to the tank so that's a plus. But does this mean my water pump is trash?

Running at idle this time of year will give you no , or very little heat. The cardboard blocking your radiator will only help build more heat as you drive it down the road, with the engine under load. Even with cardboard or whatever blocking the radiator it still will not make heat like a gas engine would.

The cooler running of your engine is just the nature of the diesel beast .

The coolant running back into the resivoir via that little line means your water pump is functioning. If there was no flow the water pump would be dead.

This winter for us in the east and northeast has been extremely cold. Every winter new diesel owners and this winter even those as far south as the Carolina's who have not experienced the cold to the degree that this winter has brought, wonder the same thing about their cars. " Is my car working right? Where's my heat?"

Think of it like this, having frozen toes is the trade off for getting 50 mpg

 

[turboboost1]

My '03 was running cool and I didn't think much of it until I researched it on here and learned that the temp gauge reads what they (VW) think you should see. I'm running an Advance mid-price (OE replacement) T-stat which (with the original housing minus the pins) fixed the problem.

I think that the big thing with the OE T-stat is that it needs to correctly block an internal port. If your replacement didn't measure up (mine did), that could be part of the problem.

Another thought, are the coolant glow plugs working? Check this out: http://forums.tdiclub.com/showthread.php?t=435144

What are "coolant glow plugs" ???

 

[IndigoBlueWagon]

There are three glow plugs on the coolant flange on the back of the engine of rotary pump manual transmission TDIs. They help heat up the coolant. However, if they fail they don't throw any codes, so many folks may be driving around with faulty ones and not know it.

 

[macoombi]

I think this is normal. I can watch my gauge slowly dropped while sitting in stop and go traffic. I figure the engine just doesn't make any heat without any load and the heater fan can pull heat out faster than the car can make heat.

 

[Abacus]

It still sounds suspicious to me since the temperature shouldn't fall that quickly. The coolant glow plugs also turn off around 130°F.

Run a radiator block of some type and see how it does then. The temperature gauge is dampened so it should stay close to where it should for a longer period of time. If it's dropping while you're sitting at a light then I'll bet your thermostat is hanging open, as was suggested previously.

I run a Scangauge in mine so I can see the actual coolant temperature and even at -15°F it doesn't drop that quickly.

You can use anything for a front block, I used some heavy rubberized cloth on mine, tucked it behind the grill at the top, then folded it down and secured it with a piece of pipe insulation. I've seen the pipe insulation just tied on but can't get past the visual issue. On the lower grill I used some lawn edging and secured it with bungee cord. I'll make a better one for next winter but this one works great and cost me nothing. This is my first year running one and I am sold on them now. In addition to better warm up times my economy has gone back up slightly.

-14°F outside temp and 175°F coolant temp.