1987 300TDT Overheats on long hills - Page 3 - PeachParts Mercedes-Benz Forum

Brian Carlton · #31 09-02-2004, 12:13 PM

Quote:

Originally Posted by Alan Hamm

Regular driving in hot, humid DC weather my gauge climbs to just under 100 degress in stop and go traffic.

The SDL does exactly the same thing.

Eric Eliel · #32 09-02-2004, 12:35 PM

I don't believe anyone has mentioned that the temperature gauge reading system consisting of a sender, wires, fuse and a gauge is 17 years old. These systems (especially in the 300's) quite often don't read accurately.

The only way to verify the accuracy of your information is with a digital laser thermometer. A decent one is about $70 to $90 on ebay.

So you really don't know the real temperature, until its tested properly.

You aim it at the sending unit and read the temp of the metal sending unit base. That is the accurate reading. It will also find cold spots on the radiator AND it allows you to accurately measure the incoming coolant temperature at the thermostat housing vs. the sending unit temp. This gives you the temp rise of the coolant whiling its visiting its way through the head (generally about a 10 to 15c rise).

An inaccurate "system" gauge will give you overall temperature swing ranges AND it does seem the thread starter is experiencing too wide of a swing.

He needs to test his thermostat over the kitchen stove AND probably check the aux fan.

Alan Hamm · #33 09-02-2004, 04:19 PM

Quote:

Originally Posted by Eric Eliel

The only way to verify the accuracy of your information is with a digital laser thermometer. A decent one is about $70 to $90 on ebay.

So you really don't know the real temperature, until its tested properly.

You aim it at the sending unit and read the temp of the metal sending unit base. That is the accurate reading.

Problem is that these temperatures are rising under load. It is a ***** driving 75 MPH up a grade with the hood open and your friend standing over the engine pointing a digital thermometer at various engine components.

Sorry, I had to do it.

Eric Eliel · #34 09-02-2004, 04:25 PM

That was a pretty good one Alan!

Hatterasguy · #35 09-02-2004, 10:13 PM

My SDL never runs over 100C, maybe if I was pulling up a steep grade at 20mph with the AC on and 4 people+their stuff in the car. Even then the electric fan should come on at 105c and bring the temps down fast. On a hot day with the AC going full bore 90c is about what it runs, at 75-80mph.

BrierS · #36 09-03-2004, 06:47 AM

Having the same year & model I'll add my one year of ownership experience . . . mine has not visited the 100 mark here in the hills of NH. It flirts all around the 80 mark with typical being between 80 & where I believe 90 to be. Yesterday, with ambient temperature in the mid 70s, normal load w/o AC on and driving 50-65 mph it ranged from slightly under 80 > under 90+/-. With AC on it ranged from just over 80 > 90+/-. 133,000 miles & what appears to be a relatively new radiator, aux fan working both speeds, engine and all components under the hood quite clean.

goldenbear · #37 09-07-2004, 10:11 AM

I'm happy to report my cooling system passed its first real test with the new head yesterday upon returning from the central coast. A six hour drive with temps ranging from the upper 90's to low 100's the ENTIRE time. Two good 5+ mile, >7%, grades showed the cooling system worked as it should, just hitting 105C on the top of the second climb at 70mph under full load. Temp at the summit was 102F!

Hatterasguy · #38 09-07-2004, 11:52 AM

Good for you goldenbear thats how their supposed to run!

Brian Carlton · #39 09-12-2004, 10:20 PM

Quote:

Originally Posted by gsxr

That's definitely normal. Remember that the t-stat doesn't fully open until about 94C! It's temps of 110C+ that are not normal, unless conditions are very extreme, like the low-speed 15% grade mentioned by Danny, etc. I think most of the people here are talking about relatively low grades on USA highways, 6-8%, at 65-75mph... and in those conditions the temps should 'normally' stay under 105C even with the AC on.

I just got back from a 1700 mile trip with the SDL. I have taken it on the longest hill that I typically encounter. I-64 in West Virginia, headed west, about 10 miles before the I-77 intersection: 5 miles at 6% upgrade. 80 degree ambient. A/C on. 70 mph continuous.

Maximum temperature reached 105 degrees at the top of the grade. I presume that it was still climbing after 5 greuling miles upgrade, however, I cannot say for sure.

If it can remain below 105 under these conditions, I'm not overly concerned with it.

gsxr · #40 09-12-2004, 10:28 PM

Quote:

Originally Posted by Brian Carlton

I just got back from a 1700 mile trip with the SDL. I have taken it on the longest hill that I typically encounter. I-64 in West Virginia, headed west, about 10 miles before the I-77 intersection: 5 miles at 6% upgrade. 80 degree ambient. A/C on. 70 mph continuous.

Maximum temperature reached 105 degrees at the top of the grade. I presume that it was still climbing after 5 greuling miles upgrade, however, I cannot say for sure.

If it can remain below 105 under these conditions, I'm not overly concerned with it.

That's pretty much normal as long as it tops out at 105C, and I would not be concerned either!

swogee · #41 09-15-2004, 02:02 AM

Here's an update on the overheating problem.

The changing of the thermostat did not cure the problem.

I took the 300TDT to a different mechanic who happens to own a 1987 300D and he looked the cooling system over. He says the fan clutch is dead, and the lower engine encapsulation that is missing also helps to cool the engine since it has an air dam on it.

So at this point it looks like GSXR is right. The fan clutch is the culprit. Since I have the original metal fan, I am assuming that I will have to replace the fan/clutch as unit. Can the fan/clutch be replaced without special tools if I take the radiator out? If I can avoid spending $160 on tools that would be great.

Also, I noticed the vacuum pump is original, and I want to replace it. When replacing the vacuum pump, is it easier to have the fan and radiator out of the way?

Thanks for all of the replies.

-Steve

gsxr · #42 09-15-2004, 11:29 AM

Hi Steve,

Glad you diagnosed the problem - just make sure there's not a cold spot in the radiator in front of the clutch, or the clutch won't engage. Anyway:

1) The lower sound panel doesn't drastically affect engine cooling. I've driven the car with and without it in various conditions and it is almost entirely for noise encapsulation, along with some high-speed aerodynamic improvements (100mph+). I recommend installing it, if you still have it... btw, a new one is ~$250.

2) If you pull the radiator, the clutch is easy to get out. However I would buy the stubby socket from the dealer ($5) and make the spinner tool ($10 in parts) so you can pull the clutch with the radiator in place. Pulling the rad is NOT fun. With the tools you can have the clutch out in under 5 minutes. The "holder" tool, I'm told, can be done without by using a small Allen wrench in the water pump pulley hole (I have not done this personally but many others have.) The tools are shown here:
http://www.meimann.com/images/mercedes/W124_stuff/OM60x_serp_belt_tools.jpg

3) It will be MUCH easier to replace the vac pump with the fan clutch out, and probably the serp belt removed as well (also easy with the fan out). If your new pump comes with the "dam" gasket, you MUST remove the metal basket behind the pump. If it includes an "outline" gasket, you can leave the basket in place. More details in this PDF (1.5MB) :
http://www.meimann.com/docs/mercedes/OM603_vac_pump_mod.pdf

4) If the clutch bearing is ok (wiggle the blade front to back - if sloppy, the bearing is shot), you can refill the clutch with silicone fluid to repair it. This will save you ~$200 compared to buying a new clutch.

Hatterasguy · #43 09-15-2004, 06:32 PM

On the SDL I just need to pull the plastic fan shroud forward, and then their is a big allen bolt holding the clutch in. 12mm I think maybe? I should remember I have probably removed it 1/2 a dozen times in the past few months.

swogee · #44 09-17-2004, 02:12 AM

GSXR,

I have a few questions about the tools needed for removing the fan and clutch assembly.

What is bolt spinner (p/n 120 589 14 07) for? How does it work? What stuff did you use from Home Depot to make the tool? The picture shows a top view, but it isn't clear to me what is at the end of the spinner. I can see what the stubby socket and the water pump pulley holder are for. The shop manual seems to show that the there are some screws on the face of the clutch that need to be removed to take the fan clutch and fan off together. Is there enough space to get at the screws when the radiator is still installed? The shop manual states that the radiator should be removed, and I am a little worried about inadvertently putting a hole in the radiator. However, if I can pull the fan and clutch without taking out the radiator that would be great.

Finally, the vacuum pump pdf file on your web site mentions after installing the vacuum pump to pour 50 cubic cm of oil into pump before reconnected the vacuum lines. The Mercedes shop manual I have says nothing about pouring oil into the pump. Am I correct in assuming that pouring oil into the vacuum pump is not necessary if there is not an engine problem?

Thanks for all the info,

-Steve

dquance · #45 09-17-2004, 02:36 AM

Steve: I replaced my clutch last year, and I don't recall any special tools required. I did not remove the rad, just the 2 piece shroud, as I recall the inner half stays until the fan blade is removed. Then remove the belt.
The fan may have 3 - 10 mm bolts or hex bolts. I dont recall the exact size of the clutch bolt, but holding the clutch was done with a large screwdriver or bar as best I can recall.

Definitely replace the vacuum pump while you have the fan and belt off. The oil is to prime/lubricate the pump. Nothing to do with the engine.

If you get a new fan, check it carefully, the new one I received was a bit wider and larger, and would nick the shroud when the engine was under stress, I had to re-install the original.

Doug
87 300TDT
74 280C