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Matt Petty 07-06-2003 01:41 AM

Hi, I ran out of diesel and since then my 300td has...
run quite a bit hotter, according to the gauge.

I'm new to this board and am very impressed with the weatlth of previous posts. I've searched the forum for my particular problems and have formulated a few theories.

Here is what happened: I ran out of diesel in my 1979 300td about 2 gallons prematurely. I ran the car about a mile with it sputtering and trying to die at low rpms. Fill-up and the wagon runs fine after a couple of seconds. Since about a day later my temp gauge, on the freeway, has read from 175f to just under 200f. Before this change in temp I was rock solid at 175f regardless of load, even really tromping on it. Now the temp. fluctuates much more depending upon load. It also seems to heat up a bit faster. I haven't owned the car for very long but I would swear that the hot idle is a bit shakier also. I realize that mt new temp. is acceptable, but it has changed quickly and I do not trust the car anymore in extreme temps.

So far I have spun on a new fuel filter, new thermostat and coolant (old was rustynasty).

To begin to troubleshoot this problem I am first going to do a comp. check and valve adjustment just to start removing variables and to learn the procedure. I'll change the second underhood fuel filter as well as the tank screen. Probably flush out the tank.

My questions are:

1) Could grit from the tank have caused this by blockage of one of the three fuel filters resulting in constant mild fuel starvation?

2) Could grit have made it past the filters and into the IP or lift pump or injectors and caused the jump in temperature? Remember that I ran it for a bit while it was sputtering.

3) Could air be in the system? I am unclear on bleeding procedures and can see small bubbles in the second transparent fuel filter.

4) Whatelse could it be?

Everybody seems to like a challenge in this forum. Please ask any questions which may help troubleshooting. Hopefully I will have my skills down to the point of helping someone else out soon.

engatwork 07-06-2003 08:29 AM


coolant (old was rustynasty).
This statement alone would make me pull the radiator and have it cleaned. Did you drain the block when you changed the coolant? Personally, I don't think running out of fuel caused the running hot issue. What was the "mix" that you put back in? You may need to run some of the cooling system flush through it.

oh yea - welcome aboard:).

leathermang 07-06-2003 08:33 AM

One of the most frustrating things in dealing with machines is when two things happen at about the same time but are not related.... I suspect this to be the case just like Jim says....
However, you should also check to see if you have any algae indications... are you using a clear 90 degree inline filter ?
Also, if you have not been good about the coolant system, or the car is really old ( and yours is )...then I suggest at the same time you pull the radiator and clean it that you pull the core plugs ( freeze plugs ) and use a 90 degree tip on a pressure washer to flush everything out of the coolant passages ,,,, do it untill they run clear water... parts of the block always have places where the coolant flow is less than others.... and just like bends in the river are where the gold nuggets get deposited.... stuff accumulates from the rest of the block into cavities in those areas....
Too often on these old Mercedes blocks people do rebuilds without taking everything apart and having the block VATTED.... so at some point this catches up with some owner with lessened thermal capacity of the coolant to take heat to the radiator...

MVK 07-06-2003 09:38 AM

It appears like two unrelated events happened at the same time.
So dont try to co-relate them. Just concentrate on the overheating part.
i.e. coolant, coolant/water ratio, air in the coolant system, thermostat, temp sending switch(or its connector if any) etc.

On my 85 300DT temp needle jumped for a few days after the coolant and thermostat was changed. It was bleeding the air bubbles out itself during this time. Now the Needle is steady.


Matt Petty 07-06-2003 10:38 AM

Yeah, coincidence was my first instinct. I flushed the cooling system, sorta, but couldn't find the drain plugs on the block. Where are they? How high up and whereabouts?

Is bleeding the cooling system as simple as using the bleeder bolt on top of the thermostat?

How do you check the fan clutch?

Thanks for the help!

leathermang 07-06-2003 11:48 AM

"I flushed the cooling system, sorta"= " I did not really flush the cooling system "

The block drain plug is low on the front passengers side of the engine...

The block core ( freeze plugs ) are in a line on each side of the block . They are about an inch and half in diameter. One of the will probably have a block heater plugged into it... typically the back one . Get new Brass plugs before you start, then take them out and flush with as hard a stream of water you can manage until the water is clear coming out of all the orifices..

Matt Petty 07-06-2003 04:17 PM

Thanks, sounds good. My "sortaflush" was a very involved halfassed attempt. I used two cans of flusher and ran and dropped five loads of coolant. It changed from verymurky to prettymurky. So I'll get my pressure washer out and blast away.

Are you describing a drain plug, plus two freeze plugs on either side or a drain and two freeze plugs total?

Thanks in advance!

william rogers 07-07-2003 02:56 AM

after fill of new coolant dont forget to put heater on highest setting and let run car for ten or so minutes ..........
William Rogers........

300SDog 07-07-2003 12:09 PM

Maybe not coincidence !!! Am professional truck driver who has been warned against running diesels out of fuel - causing permanent damage to the engine.

Basically, engines starved of fuel continue to combust "dry"..... without lubrication of combustion chambers, internal parts (valve seats, pre-comb chambers, etc) can get scorched.

Look for oil in your coolant system. Also check engine oil for water bubbles while engine is running.

Maxwell 07-07-2003 12:29 PM

That sure sounds nasty, i'm definitely carrying some emergency fuel now. No Limping home for me

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