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Old 15th September 2020, 19:49   #1
75driver
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Default What’s “too hot” for a diesel?

The latest auto diesel was only getting up to 70 deg, so installed a specialist components housing and an 88 deg stat from motaquip, FTS104.88 / VTK169, in the top hose.
From cold, and monitoring temperature via obd, it initially reaches 98 deg, before dropping.
After initial cycle, it generally reaches 93-95 before dropping.
Also, if it was steady state at say 89, and I put some load on the engine (going up a hill), I’ve seen it go to 98, and expect it would go higher on a longer hill.
But, I have also noticed it dropping after 91 has been maintained for say 2 minutes.
This makes me think that the stat opens very slowly.
I know the slow speed fan kicks in at 100, but what is the consensus on running at these temperatures on a diesel?


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Old 15th September 2020, 20:10   #2
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That sounds high, but maybe its just mine that runs cool.

Mine settles at about 84/85 highest I have ever seen is 87.
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Old 15th September 2020, 20:36   #3
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Originally Posted by Mike Trident View Post
That sounds high, but maybe its just mine that runs cool.

Mine settles at about 84/85 highest I have ever seen is 87.

87-89 is about right mike, but I’d say 84-85 is well within normal range, going by my other cars.


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Old 15th September 2020, 21:55   #4
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I had similar figures when I first fitted an inline stat. A bit concerned but after a couple of days running, temps settled between 81-85. It will reach 88 uphill on a hot day but quickly drops.
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Old 16th September 2020, 01:00   #5
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Quote:
Originally Posted by 75driver View Post
The latest auto diesel was only getting up to 70 deg, so installed a specialist components housing and an 88 deg stat from motaquip, FTS104.88 / VTK169, in the top hose.
From cold, and monitoring temperature via obd, it initially reaches 98 deg, before dropping.
After initial cycle, it generally reaches 93-95 before dropping.
Also, if it was steady state at say 89, and I put some load on the engine (going up a hill), I’ve seen it go to 98, and expect it would go higher on a longer hill.
But, I have also noticed it dropping after 91 has been maintained for say 2 minutes.
This makes me think that the stat opens very slowly.
I know the slow speed fan kicks in at 100, but what is the consensus on running at these temperatures on a diesel?
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As it sits, I wouldnt be overly concerned. But I would keep an eye on it in case it is a faulty stat. More because it is new. If it maintained this function consistently, I would then I would not be concerned. Remember, BMW struggled with getting the temperature up to high 80's. Any I have had fitted (just in the hose) has always displayed 1 or 2 degrees less than the rating of the stat fitted - coming to the conclusion that there is a 1-2 degree discrepancy between the standard location, and the location in the top hose. I would question if it was an 88 degree stat. and not perhaps a 92-94. I did try to find a 92 in hose stat for my car (which I was hoping to get 90 degrees from), but they were silly money, and coming from eastern europe, so settled on the 89.
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Old 16th September 2020, 01:52   #6
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I think you have a little air in the system after fitting the inline stat did you raise the header tank as high as you could when you refilled the system, and let the engine run a while, then slowly pen the bleed screw on the hose next to the FBH if you have one?

Once you have done that take car for a good run with the OBD on 19 then 7 so you can read the temp as you drive once it get to the 92 -96 if it does open the A/C on HIGH then watch the reading go down.

Once back home let engine run on tick over again watch the reading if fluctuation then use the bleed screw again.

1

2

3

4

5

Check it again over the next day or so for level.
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Old 16th September 2020, 10:04   #7
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I've always had a radical (scientist's) view on this. Most petrol engines run in the mid-90s and members are perfectly happy with that. They'll almost certainly worry of it drops to much below 90°C. Why should a diesel not be encouraged to run in the same range? By doing so, its inherent thermal efficiency will be better utilised. Though using different fuels, they're both heat engines, so keeping the block 'cool' reduces the energy available for work. I remember reading a comment from a forum member who was associated with a haulage company running lots of lorries. To minimise operating costs, their philosophy was to keep their diesel engines 'hot enough to fry eggs'.

EDIT: Just to add the point that actually getting the M47R to reach 90°C as the normal running temperature may not be easy to arrange. Some examples also run cooler than others, but the in-line stat modification generally proves that it can be done. I guess the question is how far?

TC

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Old 16th September 2020, 17:20   #8
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Quote:
Originally Posted by Arctic View Post
I think you have a little air in the system after fitting the inline stat did you raise the header tank as high as you could when you refilled the system, and let the engine run a while, then slowly pen the bleed screw on the hose next to the FBH if you have one?

Once you have done that take car for a good run with the OBD on 19 then 7 so you can read the temp as you drive once it get to the 92 -96 if it does open the A/C on HIGH then watch the reading go down.

Once back home let engine run on tick over again watch the reading if fluctuation then use the bleed screw again.

1

2

3

4

5

Check it again over the next day or so for level.

Quote:
Originally Posted by Arctic View Post
I think you have a little air in the system after fitting the inline stat did you raise the header tank as high as you could when you refilled the system, and let the engine run a while, then slowly pen the bleed screw on the hose next to the FBH if you have one?

Once you have done that take car for a good run with the OBD on 19 then 7 so you can read the temp as you drive once it get to the 92 -96 if it does open the A/C on HIGH then watch the reading go down.

Once back home let engine run on tick over again watch the reading if fluctuation then use the bleed screw again.

Check it again over the next day or so for level.

Thanks Arctic.
Yes, header tank was raised as high as it could go, bled through FBH bleed screw and then engine run with expansion tank cap off for a while until temp reached 60, before putting cap back on. But I’ll redo at the weekend anyway, using the bleed screw with engine running.


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Old 16th September 2020, 19:00   #9
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Quote:
Originally Posted by T-Cut View Post
I've always had a radical (scientist's) view on this. Most petrol engines run in the mid-90s and members are perfectly happy with that. They'll almost certainly worry of it drops to much below 90°C. Why should a diesel not be encouraged to run in the same range? By doing so, its inherent thermal efficiency will be better utilised. Though using different fuels, they're both heat engines, so keeping the block 'cool' reduces the energy available for work. I remember reading a comment from a forum member who was associated with a haulage company running lots of lorries. To minimise operating costs, their philosophy was to keep their diesel engines 'hot enough to fry eggs'.

EDIT: Just to add the point that actually getting the M47R to reach 90°C as the normal running temperature may not be easy to arrange. Some examples also run cooler than others, but the in-line stat modification generally proves that it can be done. I guess the question is how far?

TC
My understanding has been that diesel engines inherently run cold because they are more efficient and hence generate less 'waste' heat which is why they always take that much longer to warm up, particularly in cold weather.
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Old 16th September 2020, 20:56   #10
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Originally Posted by kelvo View Post
My understanding has been that diesel engines inherently run cold because they are more efficient and hence generate less 'waste' heat which is why they always take that much longer to warm up, particularly in cold weather.
You are correct in your assumption that diesels ‘run’ cooler than petrols because they are more thermally efficient than petrol engines, but that does not mean they ‘have’ to run colder than petrol engines. Because diesels take time to get ‘hot’, they can have a later opening thermostat. This will allow the engine to run more thermally efficient, which means more MPG. It also cuts down on ‘shellacking’ of internal components. I can reveal a secret that I have kept for many years now. My transport manager at work wondered why my lorry used to do more mpg than any other same make lorry, over a similar type of terrain. I put a higher opening thermostat in without anyone knowing about it apart from one other driver.I did it with every lorry I drove Volvo, Mercedes, Daff.
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