TM2 Numb3rs

[lev8]

Hi Folks,
I've done about 8000 km in 10 weeks with my TM2 buddy on a 2.5TDI. Recently it has has been a bit erratic. Highway Cruising was 88-90, city was 93-95. On my last trip (2100km) it started to hwy cruz@ 93/94, city 95/96. It's winter here folks, about 24 C max, then on the return trip it went back to mid to high 80s. Is the thermostat dodgy? I can't fathom why cruising ata steady 110km/hr should give a big variation 83-96. Over to the experts

[sparkymik]

Hiya if ya have a mate who has a TM2 get together and swop em or extend his connection into your engine bay it comes with about 2m of cable, hope that helps or heaven forbid coolant circulation is dodgy

Sparky

[mikeonb4c]

Looking at the figures, city temps seem fairly consistent. Highway temps are the biggest difference. When highway cruising, I would guess differences in airflow (or the temp. of that airflow) could make a noticeable difference, especially on the surfce of the metal lump, which I'm assuming your TM2 is bolted to. So my questions would be:

1) Was the air temp. much different on the two occasions
2) Was there anything that could have changed airflow pattern over the engine (e.g. one day windy, the other day calm)

PS - this is a situation where I think the Mason alarm (or any temp gauge that measures the coolant temp, not engine block surface temp.) is more diagnostically useful , as it effectively monitors what's happening in the core

[lev8]

Thanks for the input, At 110KmPH there is a lot of wind, even if the ambient fell by say 10C it should still be ripping the heat away, as is evidenced by the sudden temp rise at roundabouts when you slow down. The cooling system seems to be stable, just a higher stable, sometimes. My only thought so far is that the thermostat is not opening consistently, so that though there is sufficient air flow to cool the engine, there is insufficient flow through the head to achieve as low an operating steady temp as it used to be. I guess I can wait and see, but a jammed shut thermostat is a bit of a worry.

[missfixit70]

For the cost of a stat & an hour or 2 to fit, flush & bleed, if you have doubts, I'd change it. The worst thing that can happen is it's still the same & you've got a spare stat.

[mikeonb4c]

Thanks for the input, At 110KmPH there is a lot of wind, even if the ambient fell by say 10C it should still be ripping the heat away, as is evidenced by the sudden temp rise at roundabouts when you slow down. The cooling system seems to be stable, just a higher stable, sometimes. My only thought so far is that the thermostat is not opening consistently, so that though there is sufficient air flow to cool the engine, there is insufficient flow through the head to achieve as low an operating steady temp as it used to be. I guess I can wait and see, but a jammed shut thermostat is a bit of a worry.

lev - it seems to me (though I could be wrong) that its not just a question of how fast the car is moving through the air. Key factors are the temperature difference between the air and the engine block and the volume of that air that passes over the block per unit time. All that airspeed/windspeed increase does is magnify (and in a non linear way) the chill factor. I see it this way (reductum ad absurdum). If the air blowing through the engine bay is the same temp as the engine block surface, it will have no effect on engine block surface temperature. Similarly, outside air at -40c will have no cooling effect on the engine block if it can't get in to replace the air around the block that has been heated up by the block to temperature equilibrium.

On the airflow front, there are two considerations:

* The engine bay is out of the slipstream
* On a windy day, wind may strike the vehicle at an angle other than from straight ahead. This could have a hard to predict influence on how thoroughly hot (insulating) air is scavenged from the engine bay.

Now if you said "Nope, I'm sure the air temp and the wind conditions were the same on the two occasions this happened" then I'd have to accept that wind and air temp unlikely to be contributing factors. But you've not said that....yet!