Thread: 300TDI overheating issue?

Originally Posted by oddsoul

Thanks for everyone's help!

Found out that the thermostat is actually starting to crack open at 90c and purchased a new one and it was opening at ~80c!

....

That's probably going to help a little, but maybe not entirely.
People think of using a lower temp thermostat, but don't fully understand how it really works.
So the thermo now opens earlier, so you won't get as much heat in the coolant initially, but if the natural tendency for the engine is to run at 90 or more degrees on the highway, under load, say with the A/C on .. then the lower temp thermostat is not really helping in such a situation.

300 tdi's really need an EGT gauge so you know how hot the exhaust gasses are when you have the boot into it(which in a tdi you probably will most of the time) and a separate coolant(or head temp) gauge.

Coolant temps are heavily linked to EGT temps, so as the exhaust temp rises, so does coolant temps. Rising coolant temps don't usually equate to exhaust temp increases tho.

Even without modding the tdi in any way EGTs can start to rise for various reasons .. you're getting lower boost(air!) hence richer fuel mixture .. or something as simple as a blocked up muffler(s).
So what happens on the highway, you try to keep up with traffic(or not hold up everyone behind 'ya) .. and place more stress on the tdi, and any number of age related variables causes the motor to heat up.

So a very partially blocked up radiator, old mufflers, worn turbo(or simply lower boost pressure).. etc, and you get overheating.

When you changed the thermostat, did you make triple sure the coolant was bled, properly and then bled properly again!
When I first started mucking about with mine, this was the one(usually simple) aspect of the Tdi's design that always caught me out(till I worked it out using 'blacknights bleed method'.
The only time I've seen my standard gauge run up into the red zone was when I stuffed up the coolant bleeding, but coolant temps usually topped less than 100°C in those conditions. Stopped bled again, everything running fine thereafter.

The couple of times I've run on a hot day tho, with the A/C on, to see how hot she'd get too(117°C tops) and with the coolant bled properly, the std temp gauge never moved past a millimeter above half way.

Originally Posted by AK83

That's probably going to help a little, but maybe not entirely.
People think of using a lower temp thermostat, but don't fully understand how it really works.
So the thermo now opens earlier, so you won't get as much heat in the coolant initially, but if the natural tendency for the engine is to run at 90 or more degrees on the highway, under load, say with the A/C on .. then the lower temp thermostat is not really helping in such a situation.

300 tdi's really need an EGT gauge so you know how hot the exhaust gasses are when you have the boot into it(which in a tdi you probably will most of the time) and a separate coolant(or head temp) gauge.

Coolant temps are heavily linked to EGT temps, so as the exhaust temp rises, so does coolant temps. Rising coolant temps don't usually equate to exhaust temp increases tho.

Even without modding the tdi in any way EGTs can start to rise for various reasons .. you're getting lower boost(air!) hence richer fuel mixture .. or something as simple as a blocked up muffler(s).
So what happens on the highway, you try to keep up with traffic(or not hold up everyone behind 'ya) .. and place more stress on the tdi, and any number of age related variables causes the motor to heat up.

So a very partially blocked up radiator, old mufflers, worn turbo(or simply lower boost pressure).. etc, and you get overheating.

When you changed the thermostat, did you make triple sure the coolant was bled, properly and then bled properly again!
When I first started mucking about with mine, this was the one(usually simple) aspect of the Tdi's design that always caught me out(till I worked it out using 'blacknights bleed method'.
The only time I've seen my standard gauge run up into the red zone was when I stuffed up the coolant bleeding, but coolant temps usually topped less than 100°C in those conditions. Stopped bled again, everything running fine thereafter.

The couple of times I've run on a hot day tho, with the A/C on, to see how hot she'd get too(117°C tops) and with the coolant bled properly, the std temp gauge never moved past a millimeter above half way.

Yeah I am still having it checked by the mechanic tomorrow.. But the thermo details in my workshop manual say it should be opening around 80c-86c. So if the old thermo is opening later (and only opening by about 2mm I might add compared to the new one which has about 10mm opening), then it would cause the issue of overheating.

Have also ordered a LCA for the 300TDI just in-case and will need to finish wiring up my EGT too!!

Will keep posted but for now im glad that the engine is running at a comfortable temp ~80-86c (checked with laser temp thermo on head, block and exhaust).

Originally Posted by oddsoul

Yeah I am still having it checked by the mechanic tomorrow.. But the thermo details in my workshop manual say it should be opening around 80c-86c. So if the old thermo is opening later (and only opening by about 2mm I might add compared to the new one which has about 10mm opening), then it would cause the issue of overheating.

...

OK. curious, is the new thermostat Waxstat or Tridon.
I saw the same thing with my old(Waxstat) vs new(Tridon) thermostats too.
The only way to get the old thermostat to 'fully open' to a similar sized opening was to have it vigorously boiling water on the stove top.
Just freshly boiled water from the kettle cooled too quickly for it to open more than the 2mm I also got.

Originally Posted by AK83

OK. curious, is the new thermostat Waxstat or Tridon.
I saw the same thing with my old(Waxstat) vs new(Tridon) thermostats too.
The only way to get the old thermostat to 'fully open' to a similar sized opening was to have it vigorously boiling water on the stove top.
Just freshly boiled water from the kettle cooled too quickly for it to open more than the 2mm I also got.

It's a Dayco thermo. Yeah same for me it had to be a rolling boil for the thing to start to open more than 2mm! That's why I was concerned that it was stuck or semi opened at normal running temperature

The Saga continues!

Mechanic checked for:
Pressure - Nada
Exhaust gases in coolant - BINGO!

Head will be taken off and inspected for any faults and then we'll all know what's going on

Bugger

Is this where I insert the

Thinking 🤔 emoji


Getterdone and while you have half the hoses off and coolant drained
Get rad rodded and cleaned and just replace the viscous fan

Replace suspect hoses and check integritybof P gasket if suspect change it out now

Steve

Originally Posted by roverrescue

Is this where I insert the

Thinking 🤔 emoji


Getterdone and while you have half the hoses off and coolant drained
Get rad rodded and cleaned and just replace the viscous fan

Replace suspect hoses and check integritybof P gasket if suspect change it out now

Steve

viscous hub can make a big difference. i put new one on and it was noticeable. if there is any oil around the centre of it, it means it's leaked its insides and is not working properly anymore

Originally Posted by roverrescue

Is this where I insert the

Thinking 🤔 emoji


Getterdone and while you have half the hoses off and coolant drained
Get rad rodded and cleaned and just replace the viscous fan

Replace suspect hoses and check integritybof P gasket if suspect change it out now

Steve

Bloody thing! Haha.. Oh well!

Will get the whole cooling system sorted apart from the A/C and the Heater matrix (thats not leaking yet! FINGERS CROSSED). It should be all sorted by the end of the week.. depending on if I can reuse the old head (i.e have it machined/faced or if I need to spend the extra cash to get an AMC head..)

Hears hoping there's nothing else to go wrong with my D1

Did manage to check the Viscous fan last night when I changed the thermostat and it seemed fine. Not slowing down under resistance or any residue near or under it. Should be good?