I have a 91 300D 2.5 turbo that I feel is running to hot. When I read the owners manual it says that as long as it stays out of the red it is OK. It runs around 100 deg C most of the time but sometimes when on the interstate at 75 or 80 MPH it will go up to about 110 deg C Is this really OK? Does anyone else have a 2.5 turbo deisel, and what temp does it run at say 90 deg F at 75 MPH? If this is OK then SO BE IT. If it is not OK then what do I do? Every thing checks ok, the fans work, 40/60 mixture, radiator clean both inside and outside, engine runs great, starts very easy hot or cold, uses no oil, coolent never drops or boils over, etc.
Thanks for any assurance or help.

__________________
84 500 SEL (307,xxx miles)

"Is this OK" by this lets say that you are not hurting the engine. But why so hot. This does not give you any "reserve" for the summer and stop and go or mountain driving. You should investigate this and fix the problem. There are a couple of things to check. The temp gauge could be off. The sensor for the temp gauge could be bad. The radiator could be collapsing, Had this happen in my 300TD. Water pump could be going bad. Etc. So either take it to a good mechanic or the dealer ($$$). A good mechanic can use a IR/laser temp probe and read the radiator. If it is not the same temp though the radiator face then its probably going bad or collapsing. Same for the engine. Use the IR/laser temp gauge to check the engine temp. it should be close to the instrument gauge. If not suspect the gauge system.

Or you can buy a IR/laser temp gauge for $50 and do it yourself.

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=91778

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

For what its worth - My 190D 2.2 runs at about 190c in the winter, now that the weather is warmer it is at 100c most of the time. Today with ambient at 80f, at 70mph it would hit 110c when climbing hills.
300SD runs somewhat cooler but will also spike over 100c in similar circumstances.

I will probably catch hell on this forum for saying this, but it is my feeling that MB cooling systems leave much to be desired. Location of the T-stat seems to cause swings in the temp not found in most engines with the stat located on the high side of the system. I changed the stat in the 190 3x in the first two months I owned it before deciding that it is just the nature of the beast.

Jim

i have never found the systems inadequate if in good operating condition.

although my dodge with cummins has a lot more reserve... it WAS designed to tow 12,000#.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I did not mean to say inadequate, just different. I have had all manner, size and make of diesel tractors, trucks and machines over the years (presently have seven) and the MB's are the only ones that don't seem to be able to maintain a relatively consistant temp. The stats just don't seem to react as they should (unless perhaps I just keep buying faulty ones, God knows I've bought enough of them). When working any other diesel hard the temp may increase somewhat (generally slowly) but then when the load eases the temp slowly goes back to normal; a function of cooling capacity.

With either of my MB's, when worked hard the temp will rise rapidly, and then temp will fall just as rapidly, often while still under load. These temp swings are often 10 degrees c, up and then down. I could be wrong (certainly wouldn't be the first time) but this seems to be a function, or malfunction, of the stat. I can't ever remember operating any other breed of diesel that functioned this way, although it just occurred to me that we did have a haybine back in the early eighties that had been retrofitted with an MB diesel engine that behaved in a similar fashion.

Jim

You must define "inadequate".

I believe that most of these cooling systems cannot handle the heat generated when the engine is under a fairly heavy load. The temperature will climb from the typical 90°C. up to say 105°C. Some vehicles will be slightly less, and some will be slightly more, depending on the condition of the radiator and water pump.

So, if you consider this performance "adequate" then so be it.

However, if you expect the temperature of the engine to remain at 90°C under all ambient temperature and engine loads, then the system is clearly inadequate.

In the case of this engine, I would strongly encourage you to pull the radiator from the vehicle and spend two hours thoroughly cleaning the cooling fins. This is not an easy task and requires some foaming cleaner and compresser air. Sometimes a low powered pressure washer can do the trick.

In 10 years of use, the fins get clogged with all kinds of foreign matter that you can't see unless you hold the radiator up to the sun. The you can see all the crap in there. Work on it until you get 75% of it removed. The temperature of the engine will likely drop by at least 5°C. under similar operating conditions.

I have to agree somewhat that these cooling systems leave some to be desired. I would be concered about driving my E300 though Death Valley, CA in the middle of the summer.

I did it in my crown vic last june in 120F heat climing some VERY steep grades with the A/C on and the car barely noticed.

well, excess cooling capacity increases weight. bigger radiator, etc. on a tractor extra weight is not a problem. on a car the performace will suffer. a mercedes is built light compared to other cars its size. lightness costs more. they build it big enough no bigger. if the temp increases on a hill it is not a problem unless it gets too high. everything is built just big enough and just strong enough, in no other way can you build a light car. if you think they dont think about lightness what other car do you know of that has aluminum door hinges? aluminum hinges must cost at least twice what the steel ones do. this is just one example there are many. that is also why a mb costs twice as much as a ford. it costs more to do it the right way... the mb way.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Thanks for all the replys. I have checked the temp of the rad with a IR/laser device and the radiator is constant top to bottom across the working surface getting cooler as I go across from left to right. The temp at the water outlet of the engine is approx the same as the indicator inside the car. I will clean the radiator outside using some cleaner. Before, I just used air pressure to clean it, but from what I have read in the above post, it probably won't help much. This is my first diesel and I have finally gotten accustomed to the diesel chatter, now I will have to get used to the higher temperatures.
Thanks again.

__________________
84 500 SEL (307,xxx miles)

I don't drive through Death Valley, but I've driven MB's of all models through plenty of 108 degree, or so, days with no coolant temp trouble at all. I think what the poster is concerned about is the temp gauge moving around a little.

The reason is related not to the thermostat, but the way that coolant is routed through the thermostat. On American cars the thermostat simply regulates coolant flow through the thermostat so it flows or it doesn't. On most MB's there is a bypass sort of arrangement that I can't describe and don't understand. That is why an MB engine will have coolant warm enough at the heater core in a very short time after starting the engine on a cold or cool morning. It seems to route the coolant through the heater while the thermostat is closed and then allows it through the radiator when it opens.

I realize that this is a poor explanation, but it is unlike other cars that I've seen.

This does NOT make the cooling system inadequate and I have no worry whatsoever crossing death valley in any MB as long as the cooling system is in good order. The only concern I would have is seeing that the fuel tank is filled before starting across.

Have a great day,

Larry Bible -

You (and the others) have confirmed the conclusion that I had reached early on; it is just "the nature of the beast".

it is a bypass thermostat. every mercedes i have ever had has one from '61 to '91. most traditional thermostats on the older us cars simply are on off and keep the water flow shut off completely until the engine reaches operating temp. this can lead to hot spots due to lack of flow. in the head area i would think.

a bypass thermostat runs all water from the pump to the block and back to the pump when the engine is cold. no hot spots. when the engine warms up the stat diverts the water so that it all flows form the pump to the rad and back to the pump. this is a superior system. it prob costs a little extra to build but it works best.

now if you remove the tstat on a benz you get some flowing back to the block from the pump and some flowing to the rad. so in cold weather it never really warms up and in hot weather you loose a lot of your cooling capacity. so never run a benz wo the t stat.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

My 240D runs between 80 and 85 in all seasons and in all conditions. I live in Alabama, and it gets pretty hot in the summer, although I admit our hills are not very high. However, I certainly would not consider it inadequate by any standards.

__________________
1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Brian,
Yesterday (Saturday) I took your advice and removed the radiator. I didn't see a lot of trash in it but it was dirty. I used a strong cleaner and a hose and cleaned it until it was completly clean. I also looked as best as I could inside and it looked clean. I then laid the rad flat on it's front (hose outlets up) and put some radiator flush in it, filled it almost full with hot water, blocked the outlets and rocked the radiator backand forth until I felt the mixture was mixed. I then continued to fill the radiator. I let it sit like that for 30 min. I also sprayed some more cleaner on the outside at that time. I then flushed it out with the water hose until it ran clean both inside and outside. The radiator flush probably didn't help but it made me feel better.
I also cleaned the condensor with the same cleaner until no more dirty water came out. So far it looks like this is the best saturday morning I have spent in a long time. The temp so far has droped about 10 deg under the same conditions, and the A/C even works better. The temp is still higher than I am accustomed to but I will have to get used to it. I'm going to do my 84 500 the next saturday I have free. It doesn't need it (it never gets close to hot) but your advice has convinced me that it is good maintaince.
Thanks again.

__________________
84 500 SEL (307,xxx miles)

I am convinced that the very fine air passages through these radiators accumulate enough debris that airflow gets restricted to a measurable degree.

I believe that anyone who has cooling issues needs to perform exactly the process that you have accomplished. Obtaining a low powered pressure washer might be even more beneficial.

Glad it was successful.

Help is what we do here.