Uh-oh our son put gas into his Diesel car!

diesel
gasoline

#1

Our 16 year old was half asleep one morning and put gas into the empty tank of his 1983 Mercedes 300CD. He called and said the car was shuddering and wouldn’t go. We had it towed and pumped out but now it has an intermittant problem. It runs fine at first, but when he stops at a light, it won’t accelerate. It starts out extremely slow and sluggish and takes about 5-10 minutes before it will accelerate to a normal speed. We’re trying to decide if it’s worth trying to fix. It has about 200K miles, and always ran well before this, and the body is in very good shape. What do you think? And how much should it cost?


#2

I would simply get an estimate for a fix at your trusty mechanic and then proceed.


#3

First off, the question of whether it’s worth fixing is a silly one-- there are a lot of people who think this was the best car ever made and if the body is in good shape there are no mechanical issues that can arise that will not be worth fixing.

However, what’s likely happened is that your injection pump has been damaged. This is the part that controls when the diesel gets squirted in and how much gets squirted in. This part gets lubricated by the natural lubricity of the diesel and if you’re running gas through it, it’s not getting lubricated. A really skilled Mercedes diesel specialist might be able to fix it, but more than likely you’ll need to get a new one, which unfortunately is a pretty darned expensive part.


#4

Yup! You run gasoline through a diesel engine fuel system, and it will take out the seals in the injectors and in the injector pump.

Tester


#5

Since it’s 26 years old, has 200k miles, and has had gasoline run through the system I might be inclined to have a compression test performed on the offchance the gasoline could have caused some piston ring/cylinder wall damage. Diesels won’t tolerate low compression.


#6

Yep, have to concur with the pump and injectors. In the 80’s my Dad worked at the Olds garage and this would happen more than you’d think with the diesels. Always towed in and major service work. Whats a rebuilt pump go for these days-mayber $500.


#7

It is possible that the injection pump is damaged, but the symptoms sound a little strange. Does it run normally the rest of the time? I’m assume you replaced both fuel filters. You can try replacing the injector pump (I think I’ve paid about $900 for a rebuilt one for that engine), but I don’t understand why that would cause an intermittent problem. Does it have any injector knock (maybe an injector problem)? Any other problems (smoke, oil consumption, coolant loss, etc)? I would take it to a good shop and have it checked out if it’s nothing obvious. Let me know if you decide to sell it. (-;


#8

About $900 for a rebuilt or about $1600 for a new one, plus a few hours of labor for installation. But those pumps are pretty sturdy and they tend to be misdiagnosed. I would have some diagnostic done before I assumed it was the pump.


#9

Possible, but I don’t see how that would result in an intermittent problem. At the moment, I think I have a broken ring in one of mine (430K miles), but I haven’t had a chance to get the compression checked (mines not intermittent). I’m probably just going to toss in a reman engine.


#10

Gas in a diesel is very bad, particularly in small diesels. Some truckers do mix small amounts of gasoline in a diesel tank during the winter to help prevent freeze up, but were talking about a couple gallons to a 150 gallon tank.

Small diesels aren’t near as sturdy as heavy truck engines and a lot of damage can occur with gas in the tank. It can ruin the seals in the injectors and injector pump. Injectors on these are probably the Bosch type and could be rebuilt by a diesel shop. The pump could also be rebuilt by a competent diesel shop. Dealerships would never consider that option, they want to sell new or remanufactured. Rebuilding an injector pump frequently costs better than $1000, it just depends on the pump some will be several thousand. Injectors shouldn’t cost that much unless the Mercedes version is some sort of hollier than thou proprietary version.

Other damage can occur to the engine itself. Diesel engines are under a lot more compression than a gasoline engine. 30:1 is common where most gassers are in the neighborhood of 10:1 Since there is no ignition system on a diesel, by the time you get enough gas in the cylinder to ignite under pressure, you have a very bad situation. Detonation can occur bending rods, breaking pistons, busted crank shafts. You can also easily create enough pressure in the cylinder to lift the heads off the block in which case you’ll most certainly have to replace the head gaskets and stud and possibly have the heads worked or replaced.

Fixing a mess like this is more than a simple matter of draining the tank. You need a competent diesel mechanic to check it out and see what kind of damage you have. It doesn’t necessarily have to be a dealership. Older diesels of that age aren’t that difficult to work on for competent diesel techs.

Skipper


#11

I’m not a Benz diesel guy so my opinion is based on VW diesel experience. About all the same I guess; Bosch.
If one has a gas engine car with lowered compression the car can be very anemic on acceleration and may require far more than the usual length of roadway to pick up speed.
Some of the older VW diesels were slow anyway and with lowered compression one could count the wheel rotations on acceleration.
A guy I used to work with had a VW diesel that was getting a bit tired and when 4 of us were in the car on the way to lunch somewhere, he would shift the auto trans into LOW gear, turn off the A/C, and nail it to the floor. Within a block or so it would sometimes approach 35 MPH!

A compression test is easy to do and the cost of this test would be much, much less than the cost of rebuilding the fuel system and then discovering after the fact the motor is flirting with junk status.


#12

is there ANY ‘trucker’ out there who can confirm the idea of ‘putting a little gas’ into the diesel tank?

are you sure you didn’t mean kerosene?

gas and diesel aren’t in any way compatible. (either for use in an engine or storing together)


#13

The owner’s manual for my 87 VW diesel permitted up to 30% (thirty per cent) regular gasoline mixed with jelled No 2. diesel fuel in cold weather to dissolve the jelling so I would tend to doubt that you damaged your Benz injection pump which is made more substantially than a VW pump. If your son’s diesel runs poorly intermittently as you state, then it can be said that it is also capable of intermittently running well. I’d try a new fuel filter before concluding that the engine is damaged. Make sure too that there is no leak in the supply fuel line that can allow air into the injection pump. The symptom that you describe is consistent with air bubbles in the fuel line. The people who pumped out the system may have left a leak in the supply line.


#14

“Make sure too that there is no leak in the supply fuel line that can allow air into the injection pump. The symptom that you describe is consistent with air bubbles in the fuel line. The people who pumped out the system may have left a leak in the supply line.”

That’s a good point, you can see if there are air bubbles by checking the clear fuel lines or the plastic pre-filter.


#15

“The owner’s manual for my 87 VW diesel permitted up to 30% (thirty per cent) regular gasoline mixed with jelled No 2. diesel fuel in cold weather to dissolve the jelling so I would tend to doubt that you damaged your Benz injection pump which is made more substantially than a VW pump.”

The earlier benz manuals allowed some percent of gasoline in cold weather, the more recent ones only allow the use of up to about 50 % #1 fuel oil (kerosine) in very cold weather. The problem with straight gasoline is low lubricity in the fuel system and it’s tendency for “pre-ignition” when injected into a 21:1 compression ratio engine.


#16
They used to do it in the old days.  Today I believe most of them know better.  I can remember back in the 70's when it was the standard recommendation, but by the end of the 70's that had changed.

#17

True, most don’t do it anymore. Back then we didn’t have winterized fuel. These days the winter diesel comes pre mixed with Kerosene to prevent that.

Skip


#18

It may also be worth pointing out that an older VW diesel has the fuel pump and injection pump combined into one unit that is mounted on the engine. There is no in-tank pump so if there is a leak in the fuel supply line (there is a return line too), it will draw air in rather than leak fuel out. An older Benz may be similar.


#19

That is correct, the “lift pump” and injection pump are both on the engine, there is no pump in the tank. I leak anyplace in the fuel line from the tank can cause air to get into the system, especially when the tank is near empty.


#20

How much of a mix are we talking about? Was it bone dry? A 50-50 mix? I can’t imagine that a few gallons . . . say $20 . . . in a tank of 20 gallons would matter that much. And what 16 year old actually fills the tank? Don’t kids usually put a $20 in and drive for awhile? Isn’t diesel a;most % a gallon nowadays? That’s only 4 or 5 gallons. Anyway, I hope for the best . . and parrot the advice given above . . . talk to a good Benz guy . . . my friend works for Cummins (now called something else) and repairs them all day long. I’ll run this by him, but I know he’ll ask what the mix was. Rocketman