Thermostat issues 01 tdi

Yesterday I smell coolant while idling, after being in traffic for 1 1/2 hours I pull in driveway check radiator hoses top is hot bottom is completely cold. Is it possible that the thermostat is failing maybe not opening ?
Car drives great, I drive it like I stole it, no overheating or anything, and heat works awesome. I find it odd that the circulation seams to be poor, and the temperature difference between the two hoses got me puzzled so far.
Anyone ever had similar issues ?


Bajan

No, sounds like your thermostat was doing its job. The ALH's temp will DROP when at idle in the cold. So long as your heat kept the cabin comfortable, and that heat exchange was probably plenty to keep the engine's temp below the opening range of the thermostat when it is cold out.

This is why idling the engine won't ever warm it up to operating temp. The engine needs to be under load for any waste heat to amount to anything in the cold weather.

Now, smelling coolant means you have a leak... this has nothing at all to do with coolant temp or the operation of the thermostat or heat in the cold.

oilhammer said:

No, sounds like your thermostat was doing its job. The ALH's temp will DROP when at idle in the cold. So long as your heat kept the cabin comfortable, and that heat exchange was probably plenty to keep the engine's temp below the opening range of the thermostat when it is cold out.

This is why idling the engine won't ever warm it up to operating temp. The engine needs to be under load for any waste heat to amount to anything in the cold weather.

Now, smelling coolant means you have a leak... this has nothing at all to do with coolant temp or the operation of the thermostat or heat in the cold.

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Ok I will check for leaks again but found nothing yesterday.

So oilhammer even if driving at highway speeds, like this morning I drove for 20 minuets at 75 mph, and when I got to work the hose was still cold. I plug in my vcds and temperature read 192f . What temperature does the thermostat open at ?

87 C is the opening level of the [stock] thermostat. So if your coolant temp at the CTS was within a couple degrees of that, that would be normal.

I run a 92 C thermostat in one of my ALHs that has no EGR cooler to help it stay at temp in the winter and provide better cabin heat. It helps, but it still isn't as good as the one with the EGR cooler intact.

Remember, the cooling system in that car (and most all newer VAG products) always has a coolant flow path through the heater core. If it is cold out, and you have the heat "on" in the car, there is a constant flow of cold (outside) air into the car and over the heater core. That exchange alone can be enough to keep the engine's total cooling system capacity from warming up to a level in which the thermostat needs to open to allow flow through the radiator. You'll get some heat by proxy on the upper hose as a result of the hottest coolant (coming from the head) seeping some heat off that way, but if the thermostat has never opened because the coolant has never gotten hot enough all the way back around TO the thermostat, then the other hose will stay relatively cool.

A warm engine is a good thing. Better for the engine, lower emissions, better fuel economy. That is why engines have thermostats in the first place.

If you smell anti-freeze, and can't find any leaks in the engine compartment, I would worry that the heater core is starting to leak......does your windshield fog up on the inside easily?


Does any body have a part # for a reliable 92c thermostat for the alh and bew?


I just installed a new oem 87c in my alh a couple weeks ago, it worked good for about a week but now it never goes above 80-82c.....even on not so cold days......regardless how I drive.

maxmoo said:

If you smell anti-freeze, and can't find any leaks in the engine compartment, I would worry that the heater core is starting to leak......does your windshield fog up on the inside easily?


Does any body have a part # for a reliable 92c thermostat for the alh and bew?


I just installed a new oem 87c in my alh a couple weeks ago, it worked good for about a week but now it never goes above 80-82c.....even on not so cold days......regardless how I drive.

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The coolant I smelt was actually inside the engine bay near the overflow bottle, the smell was slight at best . I’m confident I don’t have a heater core issue, plus there’s no lost of antifreeze, no fogging of any kind. Car runs awesome, just the I had an issue so was curious.


Bajan

The cap for the reservoir could be weak. Mine was and I purchased a new one from the dealer. I tested the old cap to find it would hold any pressure.

Oilhammer
I was off from work today and had a chance to run some test.
I started both my tdi’s at the same time this morning, letting them idle until they both reached 189f in VCDS. My 03 wagon’s coolant hoses were equal in temperature, my 01 sedan still had a cold hose off the thermostat side. I’m thinking the thermostat on the 01 tdi is partially stuck or something, but it definitely needs investigating more. Only different between the two is the 01 still has an egr cooler .


Bajan

Keep in mind, the T-stat doesn't just pop open. It's function is gradual, opening or closing. By the time coolant circulates through the rad (top to bottom) it will be cold, especially in cold weather and it will be a gradual process.

There are four sources of "return" coolant that flow across (not through) the T-stat that heats it. Those four sources all come together at various points on the black metal pipe that enters the water pump housing below and under the Injection Pump. If those sources are absorbing and dumping enough heat from the coolant, the T-stat is likely to barely open, it at all. The sources are, Heater, EGR Cooler, Oil Cooler and the Expansion Tank.......... all have constant circulation regardless of engine temperature, RPMs, etc.

Are you having to add coolant?

Although I'm not a mechanic by occupation or trade, I've changed a lot of Timing Belts, including Water Pumps. I don't think I've seen an engine that did not show signs of a weeping water pump. So, swings in temperature during this time of year can cause the WP to lose a bit of coolant which doesn't necessarily mean it is about to blow a seal.

AndyBees said:

Keep in mind, the T-stat doesn't just pop open. It's function is gradual, opening or closing. By the time coolant circulates through the rad (top to bottom) it will be cold, especially in cold weather and it will be a gradual process.

There are four sources of "return" coolant that flow across (not through) the T-stat that heats it. Those four sources all come together at various points on the black metal pipe that enters the water pump housing below and under the Injection Pump. If those sources are absorbing and dumping enough heat from the coolant, the T-stat is likely to barely open, it at all. The sources are, Heater, EGR Cooler, Oil Cooler and the Expansion Tank.......... all have constant circulation regardless of engine temperature, RPMs, etc.

Are you having to add coolant?

Although I'm not a mechanic by occupation or trade, I've changed a lot of Timing Belts, including Water Pumps. I don't think I've seen an engine that did not show signs of a weeping water pump. So, swings in temperature during this time of year can cause the WP to lose a bit of coolant which doesn't necessarily mean it is about to blow a seal.

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No I’m not adding any coolant, and my heat is great. It’s confusing to me , because I can go out and drive the car for hour at 75-85mph still when I check the hose coming from thermostat is cold, doesn’t make any sense to me. Everything looks ok in vcds .


Bajan

The hose at the T-stat is the return from the Radiator. Coolant there has flowed through the Rad and will be basically cold. Remember, as I stated above, the T-stat doesn't just pop open and let coolant flow full force......... even if it did, the cold coolant would cause the T-stat to just close again.