Author Topic: The 6.9 operating temperature thread  (Read 312 times)

revilla

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Re: The 6.9 operating temperature thread
« Reply #15 on: 06 June 2019, 09:27 AM »
Yep, that’s the warm up regulator. I’m not sure there were different versions as such, although you could set the control pressure on the lower side to allow it to run relatively rich at full operating temp.

Tim

That's the famous WUR.  A capricious piece to fine-tune... M110s have them too. It's designed, as Tim suggested, to enrich the mixture while the engine goes from cold to op temp.  It facilitates starts at cold temps together with the CSV.  However, it works on the temperature parameter only and not to compensate for the air density differences at altitude.  The vacuum line is to enrich under WOT operation only.

Fuel pressures are all spot on.  I have no reason to believe that I'm running lean, but no reason not to either.  I don't really know how to check.  In any case, no pinging or knocking ever.

Understood, the 3 fuel pressures are to spec.  How about the mixture control on the FD (the 3mm hex screw "hidden" inside). Have you tuned your rich/lean condition using that screw after pressures were set to spec? Clockwise = richer Counterclockwise = leaner. I think if you set your mixture for the altitude you live at the engine should not run hotter due to high altitude.  I fully agree though that the cooling capacity is reduced at altitude due to thin air (less flowing mass) and this situation is worse on hot days where that air is even thinner.  However, that should be taken into consideration in the design of the radiator/pump as worse case scenario + a safety design factor (i.e. extra cooling capacity available but limited at the other end by the thermostat which doesn't allow to cool "too much").  As a quick practical test I would enrich the mixture using that 3mm hex screw (if not done yet!) and try the same run to see whether the op temp to goes lower.  True 105C seems high.  The (small) swings are normal though depending on up/downhill runs.

 Cheers
Robert
W116 1977 280SEL & 1979 280SE

raueda1

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Re: The 6.9 operating temperature thread
« Reply #16 on: 06 June 2019, 09:56 AM »
Quote
Fuel pressures are all spot on.  I have no reason to believe that I'm running lean, but no reason not to either.  I don't really know how to check.  In any case, no pinging or knocking ever.

Understood, the 3 fuel pressures are to spec.  How about the mixture control on the FD (the 3mm hex screw "hidden" inside). Have you tuned your rich/lean condition using that screw after pressures were set to spec? Clockwise = richer Counterclockwise = leaner. I think if you set your mixture for the altitude you live at the engine should not run hotter due to high altitude.  I fully agree though that the cooling capacity is reduced at altitude due to thin air (less flowing mass) and this situation is worse on hot days where that air is even thinner.  However, that should be taken into consideration in the design of the radiator/pump as worse case scenario + a safety design factor (i.e. extra cooling capacity available but limited at the other end by the thermostat which doesn't allow to cool "too much").  As a quick practical test I would enrich the mixture using that 3mm hex screw (if not done yet!) and try the same run to see whether the op temp to goes lower.  True 105C seems high.  The (small) swings are normal though depending on up/downhill runs.

 Cheers
I've played with the mixture control screw a little, but not in a systematic way.  I was always afraid to mess it up and so ended up leaving it where it was.  But, given some of the other oddities I've discovered with the car, I don't have much confidence that "where it was" is where it ought to be.  Just ordered fan clutch.  I'll take it for another spin after replacement and see what it does and reestablish my baseline.  After that will come a more systematic approach to the mixture.  Stay tuned.....  :)
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: The 6.9 operating temperature thread
« Reply #17 on: 06 June 2019, 10:05 AM »
Brings to mind this movie - "Breakdown", actually worth a watch ;D


Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: The 6.9 operating temperature thread
« Reply #18 on: 06 June 2019, 10:30 AM »
Brings to mind this movie - "Breakdown", actually worth a watch ;D
LOL, just read a sysnopsis.  Love Kurt Russel.  Sounds great, will watch it tonight!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: The 6.9 operating temperature thread
« Reply #19 on: 06 June 2019, 11:01 AM »
Brings to mind this movie - "Breakdown", actually worth a watch ;D
LOL, just read a sysnopsis.  Love Kurt Russel.  Sounds great, will watch it tonight!

Pretty watchable in a 90's sort of way ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: The 6.9 operating temperature thread
« Reply #20 on: 07 June 2019, 09:32 AM »
Brings to mind this movie - "Breakdown", actually worth a watch ;D
LOL, just read a sysnopsis.  Love Kurt Russel.  Sounds great, will watch it tonight!

Pretty watchable in a 90's sort of way ;)
Yes!  Watched it last night.  Quite entertaining.  The classic red rocks, mesas, buttes etc were in southern Utah.  ALL the movies with that stuff is in Southern Utah.   And that is my high speed 6.9 proving ground.  Nothing beats triple digit speeds through that country on state roads and nobody within 50 miles.  It's like a crazy dream.  But.....    You can count on not having phone coverage.  If something happens you're screwed.  That always makes it a bit more exciting, so I really don't want to overheat.   ;D
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: The 6.9 operating temperature thread
« Reply #21 on: 10 June 2019, 05:24 PM »
Have you installed a new fan clutch? Anything over 20 years old probably doesnt work correctly.

>>>snip<<<
You are, as usual, 1000% correct.  New fan clutch just arrived (Behr).  It was immediately obvious that the old unit is toast, or something very close to toast.  It doesn't freewheel and there is some resistance to spinning.  But compared to the new unit, not much.  The new one is MUCH stiffer. I'll report on the difference before changing thermostat so the effect of the clutch isn't clouded by other changes.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0