Leaking fuel out of thermostat - 1987 300D turbo - PeachParts Mercedes-Benz Forum

a2t · #1 04-08-2006, 09:55 PM

Changed the fuel pre filter today and now the thermostat is dripping diesel fuel on my 300d turbo 1987.

Since its about summer, think I can just bypass the thermostat and go straight to lift pump? The part costs $130 and Id rather not spend the money on a car with 250k miles on it. Maybe if theres a metal version somewhere I Id be more inclined to spend the $. Is this common problem, and is there one from another model I can scout for in the wrecker yards?

Second question - this is first time changing prefilter and main filter. It took me 2 hrs of cranking to get this pig started again. I especially like the line in the manual that says the system bleeds itself. Yeah just dont plan going anywhere for a few hrs and have some good jumper cables. Is there some trick to bleed the fuel system so it starts in a reasonable time? Seein how
Im going to have to open it all back up again...fun.

Thanks

Paul

dkveuro · #2 04-08-2006, 10:10 PM

Try to fill the filters before they are installed.
Those motors will need a lot of cranking otherwise.

.

a2t · #3 04-08-2006, 10:27 PM

tell me about it...

well i ordered the fuel thermostat, its leaking all over the place so i figured i cant wait on it.

next time i change out that fuel filters i'll be sure to fill them up 1st! Man I was about to get a tow truck to haul it into the dealer before it lit off.

Diesel Giant · #4 04-08-2006, 10:41 PM

You have something wrong. It should not take more than 30 seconds or so to get a proper systems to start.

a2t · #5 04-08-2006, 11:08 PM

well it runs perfectly other than trying to prime after fuel system is cracked open. This was my 1st shot at a diesel so I probably screwed something up (although I did read the manual and it seemed quite easy). Its running great now (aside from the dripping fuel thermostat).

Hey while Ive got the resident experts online, is there some kind of manual primer pump on this car? I talked to an MB mechanic who SWEARS my 603 engine has a manual pump on it to prime system for avoiding such long, l-o-n-g cranks after fuel work. Ive looked all over but this engine is covered like a duck in the wake of the Exxon Valdez, so perhaps Im missing it.

DieselGiant, are you an MB mechanic, or do you just sell? Im guessing this Benz will get the best of my limited time (obviously, as I just bought a $135 part I didnt need 5 hrs ago).

Anyways, thanks for help so far.

dkveuro · #6 04-09-2006, 04:28 PM

There is no mechanical pump to prime the system on the electronic 300SDL.
Prefilling the filters and a good battery.

I do pressurize the tank on systems I have stripped down ...use about 2 psi .
this allows the fuel to bleeed out of the lines when I crack the unions.

Even then, it takes a good total of 45 seconds or more cranking to get the engine to run.....I just crank for 10 seconds at a time and let it rest for a few minutes.

.

P.E.Haiges · #7 04-09-2006, 10:30 PM

a2t,

Why did U replace the fuel filters? Did U notice a loss of power, especially ascending hills?

If there was no noticable loss of power, the filters did not need replacing and U wouldn't need to replace the fuel thermostat.

Sounds like another case of "if it ain't broken, don't fix it".

P E H

a2t · #8 04-09-2006, 11:29 PM

cuz Im a dumb ass and I felt like spending $135 for no reason.

Actually I was told by many Benz mechanics that the plastic fuel prefilter must be changed every 3,000 miles, with the oil change.

The main fuel filter went better, and was done because I was told to change it every 12,000. I had no idea how long it had been in there, so I figured if I was gonna crack the system and spill diesel all over the place, might as well do it all.

The problem with the fuel t-stat occured because the PO had installed some strange prefilter that did not have the 90 degree bend. I looked everywhere and couldnt fit it. All I found was the 90 degree bend one, like whats supposed to go in there. So..to install it I had to re-route the fuel lines going into the fuel t-stat back to how it should have been. I think in doing this I pulled on a cheap plastic part that had a quarter million miles on it and it broke. From what I can tell on this Benz though, there aint too many plastic parts like this. Im so used to Volkswagen maintenance where its like play toys. Everything breaks in your hands. This old benz though, its like an old bus. The oil filter is pretty cool and its housing is really strong. Someone went out of their way to make this thing rock solid, well except for that t-stat housing.

I still cant believe with all the engineering that went into this rig, it takes so long to start after filter changes. I guess if I had filled up the main fuel filter it wouldnt have been so bad.

PanzerSD · #9 04-10-2006, 12:45 AM

Okay, I'll claim ignorance......What the hell is a fuel thermostat??
do I have one on my 617??

P.E.Haiges · #10 04-10-2006, 03:30 AM

a2t,

And you believed them about changing the prefilter every 3000 miles. What a crock. Even the manual says to change fuel filters every 30,000 miles.

Think logiocally: What's the worst that can happen if you didn't change the fuel filters? The engine would loose power as enough fuel couldn't get thru the filters for the engine to develope full power. OK, eventually it would stop running. BUT, when this power loss becomes noticeable, that's when its time to change ONE of the filters. I always remove the the pre filter first because its easier to R&R and I can test it by blowing into it. If the fuel squirts out easily, the pre filter is OK and the secondary filter is the culpret.

My old '79 300SD still has the same primary filter it had 8 years and 72,000 miles ago when I got it. It would probably have the same secondary fuel filter too but the original developed a leak in the side of the can and had to be replaced. The replacement is going strong after 30,000+ miles.

Logoically, its rediculous to put a mileage figure on fuel filter changes. They don't plug proportional to miles, they plug proportional to how much dirt is in the fuel. Thus if you always have clean fuel, the fuel filters will last indefinately. Air cleaners are the same way. Someone who drives on dusty roads has to change the air filter more often than someone that drives in clean air. So putting a mileage life on air filters is also rediculous.

I'm not talking about engine oil filters here. They have a life proportional to engine mileage because soot and crud get into the oil are pretty much proportional to mileage.

BTW, the SDL 603s use a straight filter but the 300D turbos use a 90* bend filter like the SD 617 engines.

Remember: "If it ain't broke, don't fix it"

Got

The fuel thermostat sends cold fuel thru the cylinder head to warm the fuel. When the fuel from the tank is warm enough, the thermostat sends the fuel directly into the secondary filter. It works similar to the thermostat in the engine lubricating system that doesn't send oil to the oil cooler until the oil reaches a certain temperature.

This is great for WVO users. It keeps the viscocity of the WVO lower in cold weather.

P E H

a2t · #11 04-14-2006, 06:00 PM

well the motor has 250k on it and it still chirps second...so...Im inclined to overdo the maintenance rather than let it go for 70k miles. The car has been well kept for its years.

the prefilter costs all of $3 and should (read *should*) take about 1 minute to change. My case was hard due to PO using wrong prefilter type, and modifying the lines to allow for it.

Good info though, but Im sticking with aggressive mtc schedule, and hope to get many more miles off the old beast.

P.E.Haiges · #12 04-14-2006, 08:26 PM

a2t,

If I changed my filter every 3000 miles, I would have used 24 filters @ $3 each that's $72. If I changed the secondary filter at $8 as often it would be another $200. That's $272 wasted.

Besides a filter blocks finer particles when it starts to get full of dirt. So it actually works better.

P E H

Maroon 300D · #13 04-14-2006, 10:49 PM

Quote:

Originally Posted by Got_The_Benz

Okay, I'll claim ignorance......What the hell is a fuel thermostat??
do I have one on my 617??

i've never heard of one, either. Now I'm kind of wondering the same thing.

#14 04-15-2006, 12:20 AM

Quote:

Originally Posted by Maroon 300D

i've never heard of one, either. Now I'm kind of wondering the same thing.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ41S300KQHW&year=1987&make=MB&model=300-DT-002&category=All&part=Diesel+Fuel+Thermostat

psfred · #15 04-15-2006, 12:25 AM

The 603 (and probably the 601 and 602) have a fuel pre-heater in the head. Fuel is diverted through the heater when cold, mainly to heat the tank, I think.

You can get an o-ring set to rebuild them when they leak, but if you broke something, o-rings won't cure it.

You can also use a MitiVac hand pump with the reservior used to bleed brakes to prime the IP, just disconnect the return hose and attach the MitiVac and pump till fuel runs out. Much faster than cranking the engine, especially if you have pulled the pressure valve holders for some reason.

I always fill the filters with clean diesel fuel or diesel injector cleaner when changing the main filter -- avoids long cranking. I also change them with a hot engine, starts easier.

I change the filters every 30,000 miles or when I have performance problems -- much cheaper to change the filters than get rear-ended in the mountains at night when the car won't run faster than 40 mph up hills, as happened to my brother last year (he didn't get hit, but was very concerned).

Peter

Peter