Friend's 1991 overheating on mountain roads... - PeachParts Mercedes-Benz Forum

Brian Carlton · #1 09-11-2009, 11:37 PM

Quote:

Originally Posted by MercFan

"Run engine at 4000-5000 rpm. Once a coolant temperature of approx. 90-95C has been reached, the speed of th eviscous fan coupling must increase, which can be clearly heard"... so if I understand correctly: warm up the engine to normal temp, then rev it up to 4000-5000 rpm and observe the fan - if the fan speed increases then then clutch is working, Ja?!

Nay.

Sorry to disagree with the manual...........but, I'd never run that engine at 4500 rpm for an indefinite period without a load. Furthermore, it's almost impossible to keep the engine from hitting it's rev limiter when you attempt such a procedure.

Finally, the engine is making so much noise that your capability of listening for the fan clutch to engage is just about zero unless you've done it before and know what your listening for.

TylerH860 · #2 09-11-2009, 11:43 PM

I've made that exact run half a dozen times with Ol' Turbo. For sustained uphill jumps the temperature does rise, and hints at, but never gets above the century mark. I'd be curious how old and nasty the coolant is before diving into parts.

MercFan · #3 09-11-2009, 11:45 PM

Quote:

Originally Posted by TylerH860

I'd be curious how old and nasty the coolant is s.

I don't know.... but it looked like the green fluid that everyone around here hates...

Oldwolf · #4 09-14-2009, 02:19 PM

Wellll....my 2.5 behaved like that when I bought it 4 months ago. Temperatures would go up to 100C when idling or climbing a hill, especially after a highway run or a quick acceleration.

Turned out my fan clutch was bad. I installed a new one and this problem was gone.

Since then I also have replaced the coolant with Zerex G05 and Water Wetter.

Now, the engine rarely goes above 90C, mostly it stays between 80C and about 87C I'd estimate. This is in the summer too.

Running with the AC on will bump temperatures by 5C easy.

Highway cruising with AC off: 82-85C; AC on: about the same.

I went with a 40% Zerex mixture btw.

pawoSD · #5 09-12-2009, 12:42 AM

Quote:

Originally Posted by Brian Carlton

Nay.

Sorry to disagree with the manual...........but, I'd never run that engine at 4500 rpm for an indefinite period without a load. Furthermore, it's almost impossible to keep the engine from hitting it's rev limiter when you attempt such a procedure.

Finally, the engine is making so much noise that your capability of listening for the fan clutch to engage is just about zero unless you've done it before and know what your listening for.

I second that, a diesel is not a high rev engine, and I would surely not run it at 4500rpm with no load, that is bad! Drive it until it is up to these high temps it is reaching, quick pull over, shut it off, and try to turn the fan by hand, if it is stiff and won't move, then the clutch works. If the engine was running 100C+ and it still spins easily, then the clutch is shot.

On my gasser I can easily hear the clutch engage around 90C....its quite loud with the fan revving up.

compress ignite · #6 09-12-2009, 01:39 AM

With:
Good:
Fan Clutch
Correct coolant
properly serviced cooling system
fresh thermostat
operating temperature sensors
fresh surge tank cap (AKA radiator cap)

should be 80 to 84 degrees "C"

How ever if Ambients are over 100 degrees "F" And you're Freezing inside And
on an uphill grade with 800lbs in the trunk...op temps will climb.

MercFan · #7 09-12-2009, 03:35 PM

He's heading back from Glennwood Springs now - going up the Vail Pass will be the true test - told him not to exceed 95C no matter what.

He says that when he turns on the heat and runs the fan inside the cabin the engine temp goes down somewhat and helps a little - I'm sure keeping the speed down helps the most. It's cool up in high country already - which should help. Let's wish him all luck.

Does that fact with the heater running and cooling the temps help narrow anything else down for him?!

compress ignite · #8 09-12-2009, 03:52 PM

'Just lets him know the Heater Core is not totally obstructed.

sixto · #9 09-12-2009, 05:11 PM

Quote:

Originally Posted by MercFan

He says that when he turns on the heat and runs the fan inside the cabin the engine temp goes down somewhat and helps a little - I'm sure keeping the speed down helps the most. It's cool up in high country already - which should help.

Cool makes up for thinner air with less heat capacity.

Sixto
87 300D

MercFan · #10 09-12-2009, 08:14 PM

He'll need to service his cooling system - I'm assuming that means flushing the green old fluid out with water and replacing it with MB approved fluid: Zerex G-05 full strength and mix 50/50 with distilled water.

Would he need to do a citrus flush on the system or no?

If there is a good link on the procedure for doing that plz send it this way.

James

MercFan · #11 09-13-2009, 11:25 PM

Could someone confirm that the coolant needs to be 50:50 mix Zerex G-05 with distilled water?!

When is the citrus flush recommended?! Should it be done in this case?