This is the fundamental question. Let say, for argument, that I am running 10 psi boost at 3000 rpm in fourth gear travelling upgrade at 70 mph in the SDL. The pedal is not floored but the engine is working pretty hard. No visible smoke, however. The engine is presumably still getting more air then it needs.

Now, I plant my foot into the throttle. The boost climbs to 11 psi. The question is whether the IP knows that I am now at full throttle and enriches the mixture beyond what would normally be required for 11 psi boost ?

If it does this, I would like to know the mechanism on the 603. I can tell you that it is not apparent because there is no additional smoke when the pedal is floored. If it kicks down to third, however, and the rpm's climb, the volume of air and fuel is significantly increased and there will be some smoke, but not the heavy black smoke that is characteristic of an overfueled condition.

On my 1998 E300 TurboDiesel, when I ask for more power at 70 mph and press the pedal down to the floor without inducing a downshift, I get some extra particulate. In fact, I am at a loss as to how the engine would respond to a demand for more power if you did not have the abiity to chuck some more fuel into the combustion chambers. Normally the driver is the feedback mechanism that decides if the car is running as it should for the conditions. The inter-relationship between boost pressure and fuel load is not in the driver's control loop, so the only thing the driver has to manipulate is the mechanical (or electro-mechanical in some cases) fuel enrichment lever.

To address your question directly we would have to know a little more about the situation than I do. Maybe others are more knowledgeable and can pipe in. But as I understand things from a steady state running condition to increase speed or climb a hill, the fuel is enriched first, then the boost climbs, and you settle at a new equillibrium. The driver controls this sequence with his/her right foot. So, in my opinion, unless 11 psi boost only happens with fuel load at maximum (pedal floored), then yes, at 11 psi boost you can have varying degrees of fuel enrichment, depending on the accelerator pedal position. In the case I was responding to, I believe the boost pressure might have been limited to something like 8 psi, and then, when the right foot signal arrived to ask for more power by enriching the mixture directly, the boost did not go up and the mixture stayed too rich, or richer than desired by the engine controls' normal measure of goodness, resulting in increased temps and some smoke out the back.

My view on this is the driver has ultimate control since no electronics to date can understand the driver's intent and deal with it electronically. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

I don't think I was very clear on how much fuel is considered to be over-fueling. I believe overfueling to be a very dark smoke from the exhaust while a lighter smoke on full throttle I consider to be normal.

Some poor quality fuels, cold engine or worn engine wil also contribute to smoke so this shouldn't be confused with overfueling.

Overfueling will produce higher exhuast temps because the fuel will continue to burn after the normal combustion period which doesn't give the combustion gas as much time to cool before leaving the combustion chamber. High exhuast temps in petrol engines is usually late ignition timing.......similar sort of thing.

Petrol engines don't like being run lean, diesels don't like being too rich.

Some overfueling is ok, but once it starts pushing up the exhaust temps without any more power then it's a bad thing, especially with newer diesels with particulate traps and cat converters.

As for the low boost and high temps, this is more likely to occur with turbo setups without alda (IP has been adjusted) or when the ALDA or ECU isn't getting the correct boost signal. Brian Calton has already expained the other cause (smaller air excess for same HP).

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

Do you know of any mechanism in the IP of either the 617 or 603 that deliberately adds additional fuel when the pedal is mashed to ensure a "fully fueled" condition? Calibrations being varying depending on a particular vehicle, this can certainly result in "overfueling" with some engines.

I don't see it on the 603 in the SDL, and I can truthfully say the same regarding the 617. Neither of them exhibit the heavy black smoke that characterizes overfueling when they are at maximum power. Even at low rpm's, they don't put out any black smoke at full pedal application.

GSXR,

I finally have the money to fix my 300TDT.

I noticed that in your ealier posts you mention making your own bolt spinner out of items from Home Depot. I can see from the picture that some flat bar stock, a bolt with an aircraft nut, and an 8mm allen wrench are needed but I was wondering if you would be able to provide more info.

1) What are the dimensions of the flat bar, (i.e. thickness and width).
2) What lengths are the flat bar pieces cut to?
3) What size are the holes and where along the length are they placed?
4) What size bolt is used (dia. x length), and are washers between the flat bar pieces?
5) Is the 8mm allen wrench glued to the back of the short piece of flat bar?
6) Was the 8mm allen wrench cut short?

Also, would I be correct in assuming that if my 300TDT has the aluminum fan cooling fan that the whole new plastic fan/clutch must be installed since the clutch for the aluminum fan is no longer available?

Thanks in advance.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

(Bump)
Did you find anything related to this, swogee?
I am looking at some PM on my '87 300D turbo in preparation for some possible trips to LA (and the dreaded Grapevine! )

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

I have a 1997 280c, its overheating, I also live in Phx., Az. where its 116~ out.

While at low speed, low RPMs it overheats,

Was told it may be the fuse that runs the auxiliary cooling fan.

Which should kick on even when the car is off and parked right?

Anyways I was attempting to check the fuses, was told its one of the square type behind the standard fuses.

While popping out one labeled "E" I dropped it down in the hole in the body i think where the shocks are, anyways its gone,

My question is the one labeled "E" the right fuse?
Or is it the one labeled "F"

Can a tech test the fuse?

If its not the fuse, then i am told it is the fan/s itself, is that right?

Thanks alot guys Ron

UPDATE:

I finally got around to replacing the water pump and thermostat on my 300TDT. I used the OE thermostat and water pump.

I tested the thermostat before installation and it seems to start opening at 80 degreees C and it is fully open by 90 degrees C or so.

The old water pump I took out had a rusted impeller, but it looked like only surface rust. I compared the old water pump to the new one and it looked like the impeller on the old pump had no missing material. I suspect the rust on the old pump impeller was probably caused by the use of the green coolant instead of the zerex/MBZ coolant. I went ahead and installed the new pump and thermostat and filled the cooling system with a 50/50 mixture of new antifreeze and water.

I was able to test drive the 300TDT yesterday and the temperature seems to sit right around 90 degrees C around town. With the previous thermostat, the temperature sat closer to 85. Originally temperature was close to 80 degrees C with the first thermostat that was in the car when I bought it. Since I don't feel like changing the thermostat anymore, I figure 90 degrees C around town will do.

I also tested the 300TDT on Cuesta grade nearby and the temperature gauge rises up to a needle width above the 100 degrees mark (102 degrees c?) when I reach the top of the grade. My speed is 70 - 75 mph, the ambient temp is 72 degrees, and the grade is 3 miles long with a 5 to 6% incline. This is with no A/C running and one person in the car with 1/2 tank of fuel. Is this normal? I would have preferred only a temperature rise of 5 to 10 degrees C on hills but it looks like the radiator just can't get rid of the heat fast enough. Does anyone know of a drop in upgrade radiator with more cooling capacity?

I have replaced just about every part that would cause the engine to heat up. I am pretty much out of ideas for troubleshooting the overheating (or heating up) of my 300TDT on hills, so I guess I will have to live with the increased hill climbing temperature and hope that it won't crack my "14" casting head. I guess it is time to figure out why the 300TDT takes 20 seconds to get to 60 MPH, but thats for another thread.

Any ideas or thoughts are welcome.

Thanks for all of the ideas and suggestions,

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

Your temps are absolutely normal. My car does the same - will run about 100-105C under load up a grade, but never goes past that. I think the t-stat doesn't reach fully open until more like 95-97C, and if that's the case (noting that it sees INLET temps), 100-105C outlet from the head would be about right. Regardless it's nothing to worry about. With the AC on and extra weight the temp should still be in the 100-105C range, ditto if ambients are higher. I recently went up a 5-6% grade for several miles at 75mph in 90F ambients and topped out at 100-102C on the gauge.

My car is usually 90-95C around town in cool ambients, you were seeing 85C more likely due to a worn/old t-stat (which usually fails so that the car runs cooler than normal). You want temps to be in the 85-95C range, cooler is NOT better... you get improved efficiency with medium temps.

You can probably get by on 60% water is SLO.

Sixto
95 S420
87 300SDL

603 gurus:

Do you think adding Redline Water Wetter will help at all? I suppose it couldn't hurt...

Not reading back into your earlier trials (sorry), are you running max. of 50% coolant in distilled / de-mineralized water? Have you tried RedLine Water Wetter or RedLine Diesel Water Wetter?

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Gone to the dark side

- Jeff

first off. you live in CALIFORNIA!!! dump that antifreeze mix, do a thorough citric acid cleanup of the block, and get the proper 60 or even 65% WATER to 40/35% G-05/MB antifreeze in there. also lets be SURE you have the right radiator cap. your car should have the 140K mark on it. you need ALL the protection you can get!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks for the additional replies.

I am using a 50/50 mix of R.O. water and Zerex G05 anti-freeze. That is the factory recommended ratio so that is what I am using.

I have considered using the water wetter by Redline, but I'm not sure how much of a difference it makes or if it is just snake oil. I'll have to look into the water wetter and see how much it actually helps.

The cooling system cap has been replaced with a new OE unit. I believe it has a 140 marking on the cap if that means anything.

I have been reading other threads on overheating with the W124 OM603 engine and I have yet to see any definite solutions. The threads never seemed to get resolved. If I do get this problem fixed, I'll post it.

Thanks again.

-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

First - my opinion - unless you've got another TDT to test this against, if the temp climbs to 100 or even 110 and holds - I wouldn't be "too" concerned. Having another car of the same model helps to figure out if this is typical behavior or not.

Remember that 100 is only 212F, 110 is 230f. A properly maintained cooling system with a 15# cap (or thereabouts) will boil water at 239f. Adding antifreeze further increases this number to something just over 260 degrees. (The manual for my '92 300SE says the coolant boils at 266f).

No question that elevated temps beyond the normal 85-90c operating temps create additional stress on the system - affecting the weakest link in the chain (the hoses) first, following on to the radiator, heater core and headgasket. Older cars, like older people, tend to be more fragile.

The issue with overheating is more one of preventing the coolant from boiling. Think about what happens to water in a pan as it approaches the boiling point - bubbles begin to form. What are the bubbles? Water converted to steam. Steam, while a great transporter of heat, does a really poor job of absorbing the heat produced in an engine. When the water boils, the heat transfer effectively stops, and that's what causes damage to the engine - things get really hot really quickly. Oil begins to break down, thermal expansion differentials between dissimlar metals like the engine block and pistons get into the danger zone where you start to have interference between moving parts, etc.

I digress...

The suggestion for the citric acid flush is a good one. Again, the age of the car suggest that there is bound to be some mineral deposits that have formed in the radiator and cooling passages of the engine. Those deposits will reduce the cooling efficiency of the system - get rid of 'em with a citric acid flush.

Water wetter is not snake oil - it's a chemical that is intended to reduce the surface tension of the coolant so that it "grips" the surfaces of the radiator and cooling passages better.

Soap is an effective surface tension reducer, but doesn't work so good in systems involving an impeller like a car's cooling system. As an example of surface tension, on a freshly waxed car, water from the hose will bead into small drops - but soapy water won't. It's an exaggeration of the conditions inside the engine and radiator, but the concept remains the same. You want as good contact between the water and the system surfaces as possible - a water wetter helps with that.

Best bet is to get the system as clean as possible.

Also - again given the age of the car, is it running the original water pump? I've seen many situations where the original pump, although not leaking or squealing, had so much corrosion (in the case of pumps that use cast-iron impellers) and/or mineral deposits that the pumping efficiency was greatly reduced. Poor water flow in a hill-climb situation is a bad thing. I've even seen pumps come out where the impellers were practically gone (stamped steel impellers).

I'm not completely sure about MB - but some cars use a spring inside the return radiator hose (usually the lower hose), to prevent the hose from collapsing under high engine (and consequently high water pump) revolutions. You can test this by getting the car up to temp and opening the throttle to produce the same number of revs as you see climbing the hill and watching the return hose for deformation.

What speed are you climbing the hill at? If the engine is "lugging" (running slowly in a higher gear), that will reduce the coolant flow and allow the heat to build. Downshifting to a lower gear and letting the motor "sing" a bit will help ensure good coolant flow and lower engine load.

A TDT is a big car with a "low power" motor - the turbo is going to cause it to run hotter anyway - don't let it lug on the hill - downshift (obviously don't redline it) and see what happens - assuming of course you can maintain a speed safe for the roadway conditions in the lower gear.

Good luck.