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  #1  
Old 06-22-2008, 03:07 PM
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81 300SD Running a bit hot

It's summer and outside temperatures are up to 105F +.

Probably, it is normal the way the 300SD runs, but since I am going out to the desert in a couple of days, I wanted to make sure I check everything.

I replaced the thermostate it has a 80C now. There was a 75C in it. Temp gauge shows the same, close to 90C in this kind of heat. Yesterday, the aux fan came on, which is really rare.
(I suppose the mark between 80C and the top white mark next to the red one <120C>, indicates 90C)

I am wondering, because I also replaced the thermostate in the 300D (80C) and it stays right on the 80C mark under the same driving and outside temp circumstances.

What else should I look for? I know there are a lot of elements throughout the cooling system, but what would be an obvious catch. Coolant level is up fan clutch seems ok, no belts slipping.

I should mention the 300D (also turbo) has no A/C belt. I have no need for it in that car. But, I never run the A/C in the 300SD

Else, maybe I should have the radiator checked...?

However, temperature is steady and no overheating so far, just a bit warmer than usual, when the outside temps are cooler it also runs cooler, unless I go uphill, in which case it will go up to the same level. But here I am not too surprised since the 300SD body is prolly heavier than the W123.

Any suggestions?
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Old 06-22-2008, 03:22 PM
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To be honest with you I have always assumed the mark between the 80C and the 120C was 100C. I certainly could be guilty of Assuming. But the distance and placement about half way between the two lead me to believe this was the case.

Doing the math half of the difference between 80 and 120 is 100. Which is exactly where the mark is.

But, unfortunately, I have learned not to trust that gauge on mine because I consistently get 10 degree cooler reading with an Infrared on the hottest area I can find (the area right behind the thermostat as its coming out of the head/engine) from what that interpretation of the gauge point really is at that middle mark. If I am wrong concluding that mark is 100C rather than 90C then this would mean the cars Temp Gauge is reading correctly.

What say you folks? Is that mark 90C or is it 100C?
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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
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  #3  
Old 06-22-2008, 03:49 PM
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I don't object your assumption. I too thought it was the 100C mark, but thinking it is 90C just makes me feel a little better.

However, the watertemp stays just below it, maybe half way or 3/4 up from the 80C mark. At a current outside temp of 100F -105F.

Out in the desert it will be 110F -120F maybe even higher, usually the gauge shows slightly below the dubious mark of 90/100C.

I think I will be ok, I was just wondering why the 300D indicates a straight 80C. Could be the gauge, but than, yesterday the aux fan came on, which is about correct once the temp starts hitting 100C ...

...So, I suppose it is the 100C mark and as long as I stay below while cruising, I should be fine ...

I could take the thermo out, going through the desert, how's that? But I thnk it won't seal, because without the thermo, there is no pressure level for the rubber gasket.
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Old 06-22-2008, 03:57 PM
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I was actually hoping YOU were correct in it being 90C! LOL....

I can tell you that you should really shoot a Infrared Thermometer around in there and see if yours is off, of at least get the real reading.

I found something recently that no one seemed to comment on that the actual opening of a thermostat is a gradual thing and just starts to open at the rated temp and doesn't fully open for about a 10C range. So that a typical thermostat is not open until around 90C anyway.

There is also a fair number of things I have read about drilling some hole sin the sides of the thermostat to increase the pre-heat flow. But eventually it runs where it runs.

I can also tell you that, so far I have replaced my radiator, coolant, thermostat, temp sender, recovery pressure cap and still I run around 95C to 105C (assuming that middle mark is 100C) on the gauge. But yet when I shoot the hottest are area of the motor, where that coolant it coming out the hottest and its surrounding metal, the hottest areas I can find consistently are from 83 to 91C. So my gauge is lying to me. By about 10C. And I too have seen some hot days, 100F here a few times and it does seem to settle in at that temp. But the REAL engine temp is what I find on the Infrared, not the gauge it seems.

Now, also remember that aux fan is triggered by the AC condenser too.
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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

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Last edited by cphilip; 06-22-2008 at 04:06 PM.
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  #5  
Old 06-22-2008, 04:19 PM
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If you stay below 100C. in 105F. ambients, you've got absolutely nothing to worry about and I wouldn't do anything to the vehicle.
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  #6  
Old 06-22-2008, 05:14 PM
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I also have assumed the mark between 80C & 120C is 100C, which would be a very nice mark to have as that is boiling point. I know that is correct in my 82 300SD as it starts to boil with plain water at that point when the pressure cap is off. I didn't think about infrared. The 80C mark is also useful because that's where the 80C thurmostats open and being in a hot climet I like my thurmostats to open at 176*F.
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  #7  
Old 06-22-2008, 06:38 PM
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Thanks guys & Brian. I feel more confident now

Usually, I stay out of the mid-day heat anyways, but just in general, the last thing I wish on myself is a breakdown out there, by the coyotes and the oxen skulls ...
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Old 06-22-2008, 09:49 PM
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So now I am back to worrying. They say it was only 94F today.

I think the 300SD runs on the hot side. Thermo is working coolant is full.

Any way to check if the waterpump is spinning at full rpm?

Could there be a worn bearing that keeps the pump from running at full rpm? ... or something like that.

Any alternative on a larger radiator for the 300SD???
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Old 06-22-2008, 10:04 PM
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Why not simply verify the gauge is even near accurate first? Then start working from there?
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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

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  #10  
Old 06-22-2008, 10:39 PM
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Quote:
Originally Posted by LaRondo View Post
So now I am back to worrying. They say it was only 94F today.

I think the 300SD runs on the hot side. Thermo is working coolant is full.

Any way to check if the waterpump is spinning at full rpm?

Could there be a worn bearing that keeps the pump from running at full rpm? ... or something like that.

Any alternative on a larger radiator for the 300SD???
There is nothing wrong with your temperatures. But, if you want to run 5-10 cooler, then remove the radiator from the vehicle and spend two hours with a pressure washer and/or some industrial condenser cleaner and get all the fine debris out from between the fins.

Or, just spend the $300. and buy a new radiator.

Either will get the engine to run slightly cooler.........which will only affect your peace of mind.........not the performance or longevity of the engine.
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  #11  
Old 06-22-2008, 11:03 PM
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Quote:
Originally Posted by cphilip View Post
Why not simply verify the gauge is even near accurate first? Then start working from there?
Yeah, I was planning to stop at the radiator shop tomorrow, he will hit the spot with an IR temp reader in all the possible places. He's a good guy he alswyas galdly does that for me. With that he can find "hot pockets" in the radiator etc.
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  #12  
Old 06-22-2008, 11:06 PM
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Quote:
Originally Posted by LaRondo View Post
Yeah, I was planning to stop at the radiator shop tomorrow, he will hit the spot with an IR temp reader in all the possible places. He's a good guy he alswyas galdly does that for me. With that he can find "hot pockets" in the radiator etc.
He can find dead spots too where the coolant is not circulating through at all and tell you if a new radiator is in order as well.

I had to put a new Radiator on because of a broken nipple but it did not change my readings because mine were simply wrong. And a new sender did not change them either. I am sort of hoping your in the same boat and find that to be the case. If not, nothing wrong with a new radiator and sender at all!

by the way... and infrared thermometer can be had for less than $100 and is real cool tool to have. Lots of uses for it, including determining if the wife has reached her boiling point or not! As if you couldn't already tell....
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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

www.cphilip.com
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  #13  
Old 06-22-2008, 11:21 PM
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Quote:
Originally Posted by Brian Carlton View Post
There is nothing wrong with your temperatures. But, if you want to run 5-10 cooler, then remove the radiator from the vehicle and spend two hours with a pressure washer and/or some industrial condenser cleaner and get all the fine debris out from between the fins.

Or, just spend the $300. and buy a new radiator.

Either will get the engine to run slightly cooler.........which will only affect your peace of mind.........not the performance or longevity of the engine.
Well, thanks Brian. I will do some pressure cleaning, at least a bit. The engine compartment needs it anyways.

I am just a bit iffy on that one.
After blowing a couple of engines in my younger years I always tediously watch for proper cooling.

Hey, did I tell you guys, about 25 years back I was on a trip across Southern Spain.
One morning, between wake up and coffee time I headed out on this back road in my bountyful white /8 220 D.
That pista was a real rollercoaster, I guess I got high on the up and down as I was shooting down the trail for coffee.

Sure enough, one of those dips pressed the car so close to the asphalt, I heard something touch down on it ... I thought of the exhaust pipe.

As it turns out, my oil pressure gauge drops out of the clouds straight to rock bottom.
Good thing I saw it and pushed the clutch immediately and hit the shut off on the dash.

As the car was stopped I look back the road and you would see the trail of oil and as I looked under the car, I could see the oil plug curled open like a tuna can.

Trust me when I say, the most sweating took place at the end of the day, after the plug was welded, the engine filled with oil about to be restarted.

It was not a nice sound, what came from the first 2 or 3 turnovers.
She took it, yet with a few grains of dust ...

Morale of the story, whenever LaRondo is piloting, the instruments are under 100% surveillance...
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Last edited by LaRondo; 06-22-2008 at 11:30 PM.
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  #14  
Old 06-22-2008, 11:24 PM
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Originally Posted by LaRondo View Post
Well, thanks Brian. I will do some pressure cleaning, at least a bit. The engine compartment needs it anyways.
Don't even think of trying a shortcut and cleaning the fins with the radiator in the vehicle. If you want to do this job, the radiator must be removed from the vehicle and the water jet from the washer must be perfectly square with the fins to prevent bending them over.

Personally, I like the chemical cleaner.
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  #15  
Old 06-22-2008, 11:34 PM
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OMG, you guys are sooo bad ... I guess I just take the other car ,

Which means I have to stop at the tire store before I go and have 'em slap on a set of new rubber ...
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