Diesel fuel filter change procedure

I understand it is good to pour type f transmission fluid into the new filter prior to install. This is for a 1995 Mercedes 300E

Is this true?

It’s a good idea to fill the oil filters with the proper oil prior to installation. But transmission fluid?

Transmission fluid is just 10 weight oil with higher detergents and different friction modifiers.

Is it just me? You use transmission fluid in a transmission, and engine oil in an engine?


It’s a good idea to fill the filter with diesel fuel before you install it, given that it’s possible. If it’s a spin-on type filter then you should be able to do that. If it’s a cartridge type filter you may not need to and there may or may not be a specific procedure to prime the system before starting. Consult a service manual.

Why you would consider using transmission fluid–or any other fluid that isn’t designed for the system–is beyond me.

I have changed many diesel filters, never used or would use anything but fresh clean diesel. I might put some Heet in the tank in cold weather but would prefer to buy treated fuel.

Some VW people do this to supposedly clean the injectors; use any type transmission fluid. I have never done this. I have often changed fuel filters w/o prefilling the new filter. The engine starts and then almost stops but does stay running until the air slug is purged. At idle speed, apparently no harm is done.


Why do you have type f atf? Your transmission uses Dexron . . .

You should fill the fuel filter before installing it.

While others may disagree with me . . . at my job, where I work on large commercial vehicles with diesel engines, I fill the fuel filters with atf

The reason is this: if I want to fill them with diesel, I have to ask the supervisor for the “fuel card” first. Then I walk over to the fuel pumps, fill the the filter with diesel, possibly making a mess, walk back with the now full filter, hopefully without spilling any.

Oh, and when I come back, I have to tell the supervisor this:
How much fuel did I get
Which pump did I use
Then he enters all this into the records

We are NOT allowed to keep fuel in containers in the shop. The only fuel allowed in the shop is the fuel in the vehicle fuel tanks.

Bottom line:

I know what I’m doing is technically wrong
I also know that doing the right thing would easily cost me 1/2 hour of “lost” productivity

Now you guys can condemn me for knowingly doing the wrong thing

There’s technically wrong and there’s productivity wrong. There’s no way I would do that for a paying customer, but for fleet maintenance I’m fine with it. Like you say, technically it’s wrong, and I don’t want the slightest chance that someone with a Mercedes diesel may have an injector pump problem and be able to come back to me and question the manner in which I changed his filter. I also know there’s a one-in-thousand (or less) chance that would ever happen. But I keep a gallon jug of diesel under the bench just to prime filters.

As far as advice to the DIY crowd, I always recommend the proper procedures. If they want to deviate from that on their own cars, fine.

BTW, what kind of company policy prevents you from keeping diesel around? Must be insurance requirements. It’s no more flammable than the waste oil drainer, far less flammable and toxic than brake cleaner, the propane in your hand torch, or the gasoline in old filters.


The safety guys at our fleet are VERY anal

We are not allowed to keep any fuel containers in the shop, as I said

At one point, the safety guys even forced us to throw out our metal oil containers (you know, the ones that hold a few quarts and have a flexible spout)

They forced us to throw them out while they watched

So, if a vehicle operator drops by and needs an oil or atf top off, this is how it goes:

The vehicle operator fills out a "trouble ticket"
The supervisor generates a repair order
I roll out the 55-gallon drum with the dispenser and connect the air line
I top off the vehicle (oil or atf)
The vehicle operator signs out the vehicle and leaves
I finish out the repair order and turn it in

It would be very nice if I could just keep those atf or oil containers on top of my bench, ready for those top-offs . . . but it’s not to be

When asked why we’re not allowed to keep these small fluid containers, all we’re told is “safety”

How does the engine respond when its fuel becomes ATF ?? Does it run normally? How do you explain abnormal operation to the customer? Will ALL diesel engines tolerate operating on ATF without problems?

If needed, I suspect there are procedures to purge the air from diesel fuel systems after fuel filter changes without filling the filter with ATF…


While I realize what I’m doing is technically wrong . . .

ALL of those vehicles started and ran normally

And the commercial trucks I work on are NOT antiquated and low tech, in case anybody is wondering

So . . . I have NOT had to “explain abnormal operation to the customer”

I can’t speak for anybody else

On my diesel Olds, I used to have to leave the outlet line on the filter loose and crank the engine to fill the filter and prime it. Otherwise you would have to crank quite a while to start it. I don’t see any reason to use ATF if you have diesel available to prime the filter.


“I don’t see any reason to use ATF if you have diesel available to prime the filter”


I DON’T have diesel available to prime the filter

Can you imagine trying to slowly fill a fuel filter with the large nozzle that is used to fill a vehicle’s fuel tank? It’s not meant to dispense fuel so slowly, so making a mess is literally impossible.

As for OP, I wish him the best

Ok thanks. This question was for fuel filter, and when I saw the German mechanic do it, I never considered that is because it is what he had laying around. It never choked or sputtered at all, he said something like whawho suggested about injector cleaning. Thanks for the replies and have a great day.

You are welcome…That’s the nice thing about diesels…They will burn a wide range or fuels without complaining too much…