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  #1  
Old 07-19-2004, 10:29 AM
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Location: Annapolis, MD
Posts: 650
300SD running hot. What's next?

I replaced the waterpump just in case, and put in an Autozone thermostat (I know, I was impatient and haved since ordered an OEM) due to high temps. In stop and go traffic with the AC on in 80 degree weather I was getting to 110 and shutting down the AC and even turning on the heat.

I removed the radiator (only 6 years old) and thoroughly hosed it out - it was very clean. I used a hose to run water back through the engine. I cleaned all the fins on the radiator and condensor. Removed and checked operation of fan clutch.

Sitting at idle for 20 minutes with the ac on (fan comes on), temp goes up to 100 in 80 degree weather.

I finally removed the thermostat and drove to work this am. Never even got to 80c on the gauge - about what I expected. On the drive home today, I'll see how hot it gets, but I'm pessimistic. I did a search on burping, but the consenus seems to be that after a while, it will burp itself.

One odd thing is that the coolant in the resevoir is never even warm. The lower radiator hose is much cooler than the upper. The radiator is hot at the top, becoming cooler at the bottom - I would assume that means the radiator is working, no?

When the thermostat comes in, I'll give it a try, but in the mean time, any ideas? By the way, a screw broke off of the t-stat housing (apparently common). I was able to drill it out a retap (english threads - gad) and put in a new screw.

My wife's new 300SD sits and smirks at me while I'm figuring out all these problems on mine. Pampered ***** (the car).

Thanks for the help!

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #2  
Old 07-19-2004, 10:49 AM
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Join Date: Feb 2004
Location: Double Oak, Texas
Posts: 296
Having just fought this war (and won), I know how you feel.

My major problem (along with new OEM thermostat and fan clutch repair) was that the outside fins on the radiator were badly clogged.

Yours outside fins are not clogged, but from your description, the radiator may be badly clogged inside. A good citric flush might help and if it does not, you are needing a new radiator.

Also, assuming your guage is accurate, 80 to 100 with a/c in stop and go is OK. Not perfect but not damaging either.

The general consensus is that running without a thermastat is not a good solution and in your case, may account for the cooler temps on the
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  #3  
Old 07-19-2004, 11:45 AM
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Location: So. California
Posts: 744
You didn't mention a few things, and you'll need to clarify them before we go off on a wrong tangent.

1) How do you know the temperature reading at the gauge is accurate? Your 20yo vehicle sensor/gauge system is notorius for inaccurate readings. Do a search, plenty of info about this.

2) Was the water pump a factory rebuild or an aftermarket rebuild (I assume you were too cheap to buy a new one from the dealer, me too!).

3) Did you test the thermostat on the kitchen stove with a meat thermometer BEFORE it was installed. In fact did you test the old one?

4) Was the Autozone thermo unit a Moto-Rad or Wahler?

5) Have you pressure tested the cooling system with a pressure gauge to determine whether you have a head gasket leak?

6) If you can locate a digital laser thermometer you can test the sending unit head temperature (normally 5 to 10 degrees hotter than the incoming coolant at the thermostat housing). You can also test the radiator for cold spots (plugged radiator).

Let us know your findings and report back to us.
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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)
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  #4  
Old 07-19-2004, 01:45 PM
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Location: Virginia
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Another possibilty is a defective A/C pressure switch. This should turn on the electric fan in front of the condensor when the refrigerant pressure exceeds a certain amount. The air across the condensor cools both the refrigerant and the radiator. If its defective, you will run hot at idle. A sepearate function causes the same fan to come on when the coolant reaches a particular temperature - 105 C sticks out in my mind, but I'm not certain and don't have time to check right now. Do a search on these for more info.
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Tjohn

82 300 SD
77 450 SL (gone)
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  #5  
Old 07-19-2004, 02:20 PM
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Location: Annapolis, MD
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Thanks guys.

Eric,
you're right I don't know the gauge is accurate, but I believe it is getting hotter than it should. When I had a slight problem with my 240D, a new t-stat fixed it, so I'm hoping that's where the problem lies. I don't have access to a laser thermometer (see below).

The water pump is new, but not OEM. The old one checked OK, but the seals were a little squeaky. The new one had more aggressive vanes which I think might make it more effective. I think the old one was OEM, since the PO always had an open checkbook for maintenance. I never tested the new t-stat, but I've had enough trouble with them to order an OEM - I'm thinking Behr. The autozone was a Stant.

The last time I had a head gasket leak in a car, I was getting exhaust into the cooling system and loosing coolant that way. I don't think that's the problem. Besides, it runs perfect without the AC - seems like the radiator just can't cope. And yes, the fan comes on when the pressure in the ac system is high enough - it runs all the time in traffic with the ac on.

I'd be OK with 100c in traffic with the AC with an outside temp of 95. My 240 in the same state never gets up to 100 ( am I crazy for selling this car? Why does a 300SD have this power over me?)

It's possible my pressure cap is defective since whenever I open it, there's no pressure, but I think that would have no effect on temp, only the boiling point of the coolant.

So, a hundred dollar weekend is past (water pump. brake caliper) and today another hundred dollars (wheel balance and t-stat, and vacuum hoses). IF this keeps up, I may get out of the MB club. Except my wife LOVES her 300SD (that smirks as I work on mine). Yesterday she said (my wife), after telling her that these cars last forever, "any car will last forever if you keep replacing all the parts!"
__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #6  
Old 07-19-2004, 02:44 PM
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Join Date: Apr 2001
Location: So. California
Posts: 744
I have not had good luck with Behr thermostats, others have. The Stant is $30 at Pep Boys and the Wahler was $14.95 at Autozone. Even the Behr isn't that much at the dealer.

You first need to get the car over to a gas station, indy or other and have them test the accuracy of the gauge. This way you'll have a point of reference. Without a reference point you are wasting time and money. You can buy one on-line for $75. While they are at it, have them check the radiator for cold spots with the digital laser thermo. Colder spots on the radiator are an indication of internal blockage in the radiator.

Are you sure the condensor and radiator are completely clean of road debris, dirt and dead bugs?

IF the gauge system is reading accurately AND there are NO cold spots on the radiator, I'd do the following in order:
1) Make sure the system has enough fluid in it by adding coolant directly into the big top radiator hose.
2) Clean condensor and radiator of bugs, debris etc.
3) Double check aux fan system for proper operation
4) Pull the thermostat and test it in the kitchen. Make sure you look carefully at not only the temp at which it opens, but also how far it opens. I like the Wahler because it opens farther apart than the Behr I tested.
5) Double check the viscous fan, do a search here and I think you'll find plenty of info about the fan.
6) Pull radiator and take it somewhere to have it boiled out. I paid $50 to have it boiled out and a seam soldered on my wife's metal Nissins. When they boil it out, all the fins are cleaned too.
7) Change back to a factory rebuilt water pump.

I'm guessing you have an inaccurate gauge system AND an improperly operating thermostat. Maybe an intermittent aux fan too, renew the fuse!
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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)
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  #7  
Old 07-19-2004, 08:06 PM
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Location: Blue Point, NY
Posts: 25,396
I'll offer another opinion regarding the SD.

Mine will show similar symptoms. It is just a question of how high the temperature will go. I can tell you that I cannot operate the SD in stop and go traffic with the A/C on with the ambient temperature above 85 or so. The gauge will immediately climb up to 100. I'm not about to find out where it stops so I roll down the windows.

My general consensus is that the system would need to have every part in it just about brand new, with no flow restriction of water or air for the temperature to remain at 95 degrees or less when running in stop and go traffic, 90 ambient, a/c on.

Both the SD and the SDL will run 95 degrees as a normal temperature when the a/c is on and the slightest amount of boost is used. Both of them can get up to 100 if the boost is on for 45 seconds or so. It does not even need to be full boost. Just a heavy pedal will do it.

I'm not really concerned with anything below 110 on both engines. I am quite sure that the SD will hit 110 if it runs extended boost (hills in PA) in 90 degree ambient with a/c.
I don't have enough info on the SDL yet, but, I would not be surprised for it to do the same thing.

I did get a benefit of about five degrees or so on the SD by removing the radiator and thorougly cleaning the fins. It is quite amazing how much crap will accumulate in there, and, unless you look carefully, you will not see any of it
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  #8  
Old 07-20-2004, 02:34 AM
greasy griddle
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My SD does the same temp thing, but my mech told me that unless the car is redlining, I shouldn't worry. So I try not to but...
What do the mech specialists here think about that advise?
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  #9  
Old 07-20-2004, 07:51 AM
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Join Date: Jul 2004
Location: Annapolis, MD
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OK, after work, I drove Hans home in 85 degree stop and go traffic with the ac on and NO thermostat. Never got over about 92c, which is about 15 degrees cooler than with the t-stat in (maybe more, since I never let it go above 105 before - I turned off the ac). As soon as the new t-stat comes in, I'll install it and see the difference. The weather is supposed to be the same for the next few days.

If you remove the fan and clutch (4 screws) , it's real easy to spray water from the rear to front through the radiator and condensor. You can see the spray pattern and how it improves when the dirt is blown out. It helps to remove the electric fan (4 screws) and clean behind it - it will have an accumulation of junk behind it.

I got the tires balanced and decided to see how good a job they did. Now I can drive 80 smoothly! The temp stays at 100 when I do that (with the ac on). Sounds about right to me.

Today, I drove my wife's 300SD to work - I'll see what she does on the commute home. I have a feeling 100c is going to be normal for both cars in heavy hot traffic witht the ac on. I can deal with that since that's only 212F. Anything over that and I get nervous.
__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #10  
Old 07-20-2004, 08:07 AM
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Location: Blue Point, NY
Posts: 25,396
Quote:
Originally posted by tenknots


If you remove the fan and clutch (4 screws) , it's real easy to spray water from the rear to front through the radiator and condensor. You can see the spray pattern and how it improves when the dirt is blown out.

I must respectfully disagree with you here. The only way to get the fins clean is to remove the radiator from the vehicle and spend about 90 minutes with foaming cleanser and compressed air to get MOST of the crap out from in between the fins. After you remove the radiator, and you believe it to be clean, just hold it up to the sun. You will see the internal fins thorougly clogged with very fine debris. The outside of the fins look perfectly clean.

Even after 90 minutes work on the SD, it still was not fully clean. I need to find a better chemical other than the Dow Foaming Bathroom Cleaner that I had around. There are special cleaning agents for condensers that would do a much better job.

You absolutely cannot clean the radiator fins properly with the radiator in the vehicle. I did not fully clean it with the radiator out of the vehicle
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  #11  
Old 07-20-2004, 09:03 AM
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Location: RI shore
Posts: 2,937
Brian is absolutely right. I just had my radiator repaired by a indy radiator shop (top seal leak) and I decided to clean it. Kerosene, lots of compressed air, brass brush and an hour of work - took a lot of crud out but there is plenty left, more than I'd like. Had no idea it would be that difficult to get that thing clean. Quick shot with a garden hose? NFW
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  #12  
Old 07-22-2004, 07:24 AM
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Location: Annapolis, MD
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Well, I drove my wife's 300SD to work Tues, and it noever got over about 90. Installed the t-stat in my car last night and at idle with the ac on, it will hit 100 (fan comes on). I don't think I've found the problem yet since without the t-stat the car never got over 85 during the same conditions.

Radiator is a Nissens with 20k miles on it. New water pump, t-stat, flushed radiator, cleaned (apparently not very well ) radiator fins, checked fan and clutch operation. The radiator is self burping through a hose on the top that leads to the overflow.

I'm missing something, but it will eventually come to me.
__________________
1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer
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  #13  
Old 07-22-2004, 08:04 AM
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Join Date: Feb 2002
Location: Virginia
Posts: 550
Quote:
Originally posted by tenknots
Installed the t-stat in my car last night and at idle with the ac on, it will hit 100 (fan comes on). I don't think I've found the problem yet since without the t-stat the car never got over 85 during the same conditions.

I'm missing something, but it will eventually come to me.
Don't forget, a properly functioning thermostat moderates the engine temperature, not just lowers it. Our T-stats are closed until I think 85 C, and will make the temperature go up faster until it reaches this point. It then opens slowly until its fully open at 94. Idling with A/C on a hot humid day normally = the highest temperatures you'll see. 100 under those conditions is perfectly acceptable in my book. At 105 C or if the refrigerant pressure gets too high the electric fan should come on (either condition will cause it to do so). If it goes up after that you've really got a problem.
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Tjohn

82 300 SD
77 450 SL (gone)
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  #14  
Old 07-22-2004, 09:02 AM
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Location: Blue Point, NY
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As a consequence of this thread, I was paying attention to the temperature on the SDL yesterday.

Operating conditions: 85 degree ambient.

I ran the SDL with the a/c off and the windows down just to see what it does. Again, when boost is used, the temperature climbs up to 95 degrees immediately. This occurs when leaving a stop light and accelerating up to 60 mph using heavy boost in third gear between 25 mph and 50 mph.

Then, with the a/c on, the temp will go right up to 100 when using heavy boost for more than 30 seconds at 65 mph in climb.
In fact, on one hill in CT, it actually peaked at about 102 degrees.

As soon as the boost is released, the temp will gradually return to 90. If the engine is unloaded completely, the temp will return to about 85.

One possibility:

There is a differential between the gauge and the thermostat.
The water temp. that the thermostat sees is not exactly the same as the water temp. seen by the gauge. Under heavy load, the temperature at the gauge creeps up to near 100 degrees but the thermostat sees water at somewhere near 92-94 degrees.
This can be the only possible explanation because, as stated in previous posts, when the thermostat is removed, the temp. never gets above 80 or so.

This would explain why the 100 degree barrier is not easy to cross. The gauge will climb right up to 100 or so, but seems not to want to go too much beyond 100. This would imply that the thermostat is now seeing hotter water and is opening further.

However, the heat produced under full boost does appear to be more than the system can dissipate. I do not think that the 603 could run at full boost for more than about 90 seconds before getting into trouble.
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  #15  
Old 07-22-2004, 09:29 AM
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Location: RI shore
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If in doubt, cook 'em! I did this with my daughter last weekend with a water filled pan on the grill using the grill meat thermometer and another dial thermometer for greater accuracy. We cooked 2 thermometers and she got to see how they both opened and closed where they should (statically). It should be noted that the position of these thermostats is also affected by flow load (according to the FSM), therefore at higher flows they are probably full open before they would be at idle for the same temperature

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