car: 300D 5 cylinder
Year: 1978
color: yellow
miles: 300,000 + (2 years with odometer broken)

for those who are having troubles with heating in there 300D's

I have been dealing with a huge overheating problem for the past 4 years and didnt do anything until now. Driving the car past the 100C mark (in my car its the 212F marker) was always the norm, eventhough the A/C wasnt even on at all. On some days, having it redline was sometimes ok for me...if i could get to point B within 10minutes.---> really!..dont ever do this in your 300D's...it really sucks!

Well I did a flush about 2 years ago...not knowing a lot about mercedes benz back then...and just drained out the old radiator fluid from the geezer and replaced it back up with a 50/50 mix of some generic brand antifreeze. I also replaced my aux fan, aux fan temp switch and thermostat but it still had all of the problems.

Time to take up the deal again. This time i drain the bastard out of antifreeze (really dark green color), not touching the engine block drain plugs and removed the whole entire radiator out (requires you to remove the transmission oil lines too). No sign of oil in the antifreeze ------>thanks god!. I sprayed out the radiator inside and outside and tons and tons of black oil and residue came out which was caught in the threads of the aluminum housing. Some shout from a local grocery store prooved a great degreaser for this job and mind you a great smelling radiator too!

Reassembled the radiator back into the car and filled, ran car for 5 minutes, drained....this procedure for 3 times (thermostat off). Antifreeze color faded from dark green to light green.

I performed the "De-oiling" technique devised in the online 300D W123 manual found at forum member: boostnbenz website. I used half a bottle of Shout from the local grocery store as then "De-oiling agent" ( recommed by some other people in this forum). and topped off the radiator with water. Ran the car for a good 30 minutes trying to reach 175F (or 80C) temp. Drained, had a ton of soapy suds come out with brown greenish water!. Refilled, ran car for 5 minutes, drained......this procedure for another 5 times to get all the Shout out.

At this point, the antifreeze is almost gone with a little bit of green left in the solution. I then dumped 2 bottles of Prestone Super Clean and topped it off with water. Drove the bastard around.

I live here in colorado and there are plenty of mountains to climb! I took the geeze up and drove her for a good 30 minutes up a mountain side, constantly going up. With the thermostat out and the Prestone Superclean flush in the radi, she could only put out half way between 175 and 200F marker!....

Damm was i relieved...

After driving her for the next three or four days (letting the Superclean kick in to remove all that rust), i plan on switching out a new radi cap, temp sending unit, and water pump. I also plan on using water wetter and a whole bottle of MB coolant..no more cheap stuff..

with a temp like that at such a great hill to climb, i must say there really is life in these guys if you take care of them well!

muybweno,

Sounds like you did a good job of cleaning your cooling system, but you have not solved the problem of the oil getting into the cooling system. It might be a leaking head gasket or cracked head.

P E H

sorry but wanted to clarify...
the oil deposits were only found on the outside of the radiator fins--> thats when i had sprayed the hell out of it with a high pressured water gun. Inside of the radiator had only green antifreeze in it. Although, when i was draining out the old fluids, it looked rather dark green. I think this was the rust build up that made it have a dark green color. I let the old radiator antifreeze fluid sit for a good couple of hours...and i didnt find any emusified oil deposites floating on top... I then knew that i didnt have any oil in the system.

I hope that i dont have a cracked head...

Congrats, cooling problems can be frustrating.

Be careful with high pressure water wash on radiator fins, they bend easily. Bent fins decrease the air flow through the radiator.

alright the quick update on the process!!!

I am still runing the super flush in the car now.. and it has been about a good 3 days since my last post on temp readings. The temperature is currently running at between temps of 175-200F, that would be around 80-100C...100C if i were to climb heavy mountains for a good 30-40 minutes on an average temp day. Note that this is with the thermostat off the car..so when its really cold, it will hardly get up to 175 if i were to drive it for a long time.

I put in a new behr thermostat in today just to see if everything else is going well. Now the temp read as it normally should after 5-10mins of hard driving. (between 175-100C). it will stay at this constant temp range even after going up hills too on hot days ....but now its running close to 95-100C after hot climbs up mountain hills...it will go down if i go down a hill but it will stay at this range of 95C most of the time....

with this kind of result, i think that i may want to change my water pump because without the thermostat...the water pump had free flow with no restrictions to the engine block. Now that the thermostats in there, it has to work a little harder to force water to the engine block..also i dont think that its working to well...i can here some squeaking sounds comming from it too..

thats next on my list...will post updates to see the difference afterwards..

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer

careful of that sqeaking sound! I had that for a while on my '78, I always assumed it was the fan clutch. It wasn't, it was the water pump. Temp always stayed normal until one day when i was driving to the Y to go for a swim. The squealing was present at as I drove down the block from home, just like normal, and then went away, just like normal. Three minutes later, in in town traffic, the temp needle was pegged at 250. I think I tempered the rings when that happened, started going through 3-4 quarts of oil per tank after that.
A rebuilt pump is only about $25 at the dealer, but the two that I had both started to squeal after about 14 months. Warranty is a year. I finally got a japanese made brand new one for about $60 and so far so good.

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andy t
'78 300d
'95 volvo 850, wagon
'86 300sdl - engine out, maybe I'll have it rolling by June

whole bunch o' bicycles

good to hear that that squeaking sound is the water pump!!!...I picked up a LASO brand one from the internet just recently and i plan on changing it out tomorrow along with draining out the rest of the acid wash flush currently in the cooling system.. they asked for 3-5 days of hard driving with at least 300-500 miles on the acid treatment for best results.

any word of advice when i do this change out on the water pump?...also i did that deoiling process in my first flush and i really want to get rid of the entire green coolant in my radiator system.. is there a special way of removing all the radiator fluid from the engine block without removing the plug that on the side of the engine block?... I finally found where that engine drain block plug is at and it doesnt seem very appealing to me to get all the way down there, removing the headers and air intake pipes just to reach it. Someone stated on using a shopvac to do this without removing this drain plug and also prooved to have better results in removing all the iddy griddy stuff thats built up in the engine...but i dont know how that would work.

remember, i want to get all of the griddy stuff thats built up in the engine block as well (ie rust particles and calcium deposits)


thanks for all the replies
allen

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer

the water pump is pretty straightforward, you will need a good open-end 10mm wrench to loosen the bolts that hold on the fan. As far as the drain plug, I was able to snake my arm in and get to the plug without removing anything except a small amount of skin. I could get there from the top, once I found the plug. If your car has the AC in place (mine does not) then you might have to go from the bottom, but I don't think you will have to take anything off to get there.

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andy t
'78 300d
'95 volvo 850, wagon
'86 300sdl - engine out, maybe I'll have it rolling by June

whole bunch o' bicycles

sounds pretty easy then.
tell me wheelguru:

what kind of socket wrench size did you use to remove the drain plug from the engine block...a 15mm?? it looks pretty big to me and i fear that since i have a 5 cylinder diesel..the exhaust and intakes are taking almost 95% of the space from the top. i definetly would need to remove the air filter housing just to even fit my hand in that area.......
you might want to show me a picture of where it actually is..i might be making this harder on myself in that mistaking the drain plug from something else...

from the bottom of the car facing the engine head on in front of the hood, the drain plug that " i'm seeing" is at the left side of the engine..right below the exhaust pipes..the throttle linkage guides me to that drain plug.

i do have A/C on the car too so i guess from the bottom its a bad idea..

If i am sucessful in removing th engine block drains...how do i prevent getting air pockets within the cooling system when i do fill it back up again? Can i just fill it through the usual opening area of the vent nut bolt located on top of the thermostat housing? or just fill it the normal way through the radiator...

sorry for asking so many questions. i just want to do it the right way and not have to waste another 12-15 bucks on genuine mercedes coolant...that stuff is pretty expensive to the regular bottle of coolant.

thanks for all the help guys
allen

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer

ooh dammit dammit dammit ...i shouldn't have thought that i could have changed that water pump!!!!


when i was taking out that water pump...2 of the five screws that were attached from the water pump to the water pump housing has broken off complete...threading still in the housing...OMG!!!!

now i'm freaking out..

stopped what i was doing and put the rest of the screws back in...finished the flush and filled with OEM MB coolant. i Plan on driving her for a while tomorrow...god i hope that gasket and its 3 super tight screws are strong enough to hold pressure of that pump!!! but then again it should because the threadings are stillin there...

yeah thats what i get for fixing something that aint broken...or necessary to replace...--> i guess i just didnt want to see my beautiful laso water pump just sitting around...waiting for the next 25,000 miles to come around for the next flush job.

also...i cant get that stupid retainer bracket that holds the A/C compressor and completely covers the water pump housing....how do you get this off??

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer

yup! so i took my 300D down to the shop for them to replace that water pump that i bought over the internet...well since the bolts were rusted off the water pump...i couldnt do the job myself due to the lack of tools and ratchet extenstions involving in the removal process of the A/C bracket that covers the water pump housing....

I had them removed the old housing and replace it with a used one that only had less than 100,000 miles on it...so it was ok for 50.00 bucks. Labor was really expensive at 90.00 per hr. so it took them a good 4.5 hours to do the job.

well when the car was finished i had strict orders for them to not put the thermostat back into the engine. I wanted to see if it can cool itself with it having a hard time to get up to at least 80C or 175F. I was wrong...
While paying for the bill, the car's aux fan was kicking on, by the time i had gotten of the shop and looked at the diesel...it was leaking radiator fluids everywhere!...

I told the mechanic that this wasnt right, and the temp gauges were reading an outstanding 250F way past pegged!!!!. well it turns out that since they had to drain all the fluids out of the engine block...the stupid mechanic didnt even bother to have the incentive that maybe the radiator was cooled and the engine was hot----> DUH! an airpocket!...

they put one of those handy air pumps to the radiator cap and started to pump with the thermostat vent bolt off. Well low and behold the radiator was empty of fluids after 20 pumps or so...refilled the radiator back up and it seemed to run at normal temps now between 90-95C idle...with the thermostat off ( just a little high for me!)


got home and the next day checked the fluid levels and guess what i see in the radiator fluid....OIL DEPOSITS!!!!!....arrrhhh!!!!!...

those bastards especially that mechanic had probably caused me a blown head gasket!!!...arrrh i'm going insane with this cooling stuff...

anyways....yup that felt good!...just wanted to get all that steam out!. I plan on doing the valve stem seals and guides myself in the next 6 months or so... so when i take off that cylinder head...that would be a good time to replace that gasket and get rid of these ultra ubber stupid cooling problems for good!...and besides i need those valve guides to reduce the amount of oil consumption in my diesel


The take home message here is:

READ READ and READ as many posts as you can before you try to do your radiator cooling problems. I am strickly a novice at diesels and did know about the precautions about blown head gaskets and temps over 100C. but if your gonna do your radiator you self...remember to VENT VENT and also make sure to VENT the radiator system before you run these bad boys!


well thats it for my little series of engine cooling...this little project had cost me well over 600.00 in labor and parts especially 3 days of time too...i should know better than this!

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer