I took my '85 300d to the shop today to have a new block heater installed. Before they started work I showed them the inline hose fitting installed in the upper heater hose at the rear of the head and specifically asked them to refill the system through it.

I happened to look in from the waiting room when they were almost done, and what do I see but the owner filling through the tank instead.

I went in and reminded him that wasn't what I wanted -- to be fair I was a bit testy, been on meds for a back sprain for almost a week and they're making me quick on the draw, temper wise.

He more or less said that's complete BS, and continued to pour. I started to say it's a rule not to fill the system on a Mercedes diesel that way and he more or less sarcastically replied that them there mechanics on the Mercedes Internet must have some darned special knowledge that no one else in the trade has, to say that.

I left furious. I know the point of filling through the upper rad hose or the rear heater hose is to avoid an air bubble, but what is the WHY behind that statement?

This is for my future reference as I am not leaving this be.

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

MB has a bypass thermostat that contributes to the problem. In other words, coolant only circulates through the block until the engine reaches operating temperature. So, the closed thermostat is reluctant to let coolant into the engine if it is filled strictly via the radiator. Better to directly fill thru the top radiator hose or heater hose to get coolant directly into the block immediately and avoid an air bubble.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Hey Mac,
Time to get a new mechanic.
That sort of arrogance causes things to be missed.
Its your car & you are paying for the job, so you get to call the shots. He needs to have that explained to him.
The only exception would be if you wanted the guy to do something that could damage it.
I hope you filled & burped after you got it back.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

Why does it make a difference where it's filled in the long run? Will the method of filling the overflow cause a air bubble to stay there past the first few extended road trips and thus cause damage to your system?

Problem is that the first time the motor gets to operating temp there will be a hot spot in the head where the air bubble is.
You risk head cracking or warping.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

How does one "burp" the system?

I hear this more often than I can count, and it's something I don't quite understand...
the expansion tank has an upper hose, and a lower hose. filling through the tank fills the radiator, and the water pump up to the thermostat, then when the rad is full, the upper hose flows the water into the head. IF, (and it's a big IF) the mechanic verifies zero air is left in the upper hose when he's filled the tank, there should be no air bubble in the head.
this is ONLY on the turbo 617's, as the N/A radiators do not have a vent line built into the cooling circuit.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Thanks SO much for pointing this out, I was starting to get real confused!

Additionally, the 617.95's have a thermostat bypass passage built into the thermostat housing.

I have to change the thermostat on the E300. Does the same technique apply to this as well or can I use the overflow?

__________________
Sent from an agnostic abacus

2014 C250 21,XXX my new DD ** 2013 GLK 350 18,000 Wife's new DD**

- With out god, life is everything.
- God is an ever receding pocket of scientific ignorance that's getting smaller and smaller as time moves on..." Neil DeGrasse Tyson
- You can pray for me, I'll think for you.
- When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.