The 84 Deville I just got is a 5.7 Diesel and so far I have had no problems with that. I was wondering, however, if I were interested in the future, what kind of work is involved in converting that to a regular engine. One of my friends had that done to an 84 he had, but it was already done when he bought it. Would it be to much work for one to do by themselves, or would it cost to much. Also what would be the benefits of such a change, and is it even recommended. Any input would help. Thanks.

ps I am very unfamiliar with diesel engines so any maintence advice or anything else that is imperitive to know would be great.

I'm also interested in hearing the responses to this one. As I understand it, these engines were awful and most all of them were replaced with gassers. These engines are held up as one of the prime examples of why the U.S. got so turned off to diesel cars to this day.

Benefits: The engine that wasnt meant to be ran as a diesel, will now last longer in its original fuel spec! It will be quieter' not only because its a diesel, but the 5.7 has thin cylinder walls that allow excess noise leakage because it wasnt meant to be diesel!



It shouldnt be that hard, but challenging atleast... It really only needs regular gas engine heads, gas fuel pump fuel lines, and a carburator or fuel injection system... but my only question would be if there is still the spot for the distributor and if it'd work with the crankshaft.

you know, the diesels only were bad becuase people ran and treated them as gas engines... I heard people that got 300k and 400k+ miles out of them and the engine/driveline was fine, only got a new car because they wanted something differnt..... who were they? TRUCKERS!

Really, diesels are not the engine to start up and run for 10min to go to the local store and back, or other quick driving... once started, they are made to run for a long time, why do you htink truckers leave the big Cats running when they are at a truck stop or something? I am sure someone that knows more aobut the diesel will be able to help you with it... I would personally keep it diesel, you never see them around anymore.... even at the least, diesel is cheaper then gas....

The "Olds" diesels were actually far more robust than people give them credit for... there was no real problem with "thin cylinder walls" ....that is a new one!!

The issue was that people treated them like gas engines and maintained them the same way....that is to say poorly. Treated properly, the engines would run forever.

Several things happened that caused problems. The most single common mistake was that most people used the WRONG OIL in those diesels. They put automotive 10W40 oil in them (since that was the most expensive "trick" oil of the early 70's...). 10W40 oil was specifically NOT recommended for the Olds diesels because the high viscosity improver concentration in the 10W40 oils and the relatively poor quality of that viscosity improver package in the oils of that era (those were SE grade oils in that time frame) caused severe ring belt deposits. NO diesel engine maker in that time frame recommended any multivis oil...much less 10W40 that had more viscosity improvers than any other product. So....people would use the 10W40 oil and it would form deposits in the ring lands and eventually restrict the ring movement and then the engine would loose compression and not start......

Which then brings us to the second big mistake people made with the Olds diesels....they used starting fluid or ether or sometimes WD40 sprayed into the intake to start them. This worked for awhile when the scenario above played out and caused a loss of compression. It would also work in the winter when they were late for work and had forgotten to plug the block heater in and it wouldn't start.... hit it with the ether and hammer down. Trouble is....the pistons in that engine were not the cast iron crowned HD pistons like in big trucks....AND the Olds diesel had much more compression (22:1) than class 8 diesels SO....the violent reaction from the ether combustion on the intake stroke would collapse the top ring lands, trap the rings and the rings would stick and loose compression. See above.

Trust me, most all the Olds diesels were "killed" by their owners in the above fashion.

I worked on those engines and I know how sturdy they were. There were NOT a class 8 truck engine...but they were plenty robust enough for passenger car use....if maintained and treated correctly. Possibly it was GM's fault for not informing the owners or promising "too much" in the haste to sell them for the fuel economy.....owners really needed to be coached and schooled as to how to treat, operate and maintain them... They are poor engines for short tripping to the post office and food store on a daily basis. But they were sold for that use. They probably should have been sold on a limited basis in the Northern states due to poor cold weather startability (as is with most diesels) and/or clear instructions in using the block heater and the importance of it should have been stressed....but, then, if people knew how much trouble they were they wouldn't have bought them....does this seem to be going in circles.???

The other issue in the early ones was the fuel gelling. Most people would buy the wrong fuel during the winter (of course the cheapest fuel was the wrong fuel....) and the fuel would gel and plug the fuel filter. So the can of ether came out of the trunk....see above. Later models of the engine came with an electrically heated fuel filter to avoid this problem. Probably should have been there all along...but....if the right fuel was used, then it wasn't an issue to begin with.

One other "problem" that came up in operation was people's haste to start them....they would not wait for the glow plugs to warm up the engine (and they didn't use the block heater in the winter of course) and they would just start cranking. Then they would remember the glow plugs...trouble is , now there is all this fuel in there. So...they would crank and crank. Then they learned how to "jump" the glow plugs to turn them on longer...trouble is, then the glow plugs would burn out. When the glow plugs burned out and melted they wouldn't come out of the combustion chamber...so the mechanic/owner forced them...and the tips broke off and stayed in the chamber....where they were crushed by the piston the next trip around....with 22:1 there isn't much room in there and the resulting damage would take the engine out. Is this the engine's fault???? the mechanics and owners claimed it was. I cold never burn out a glow plug using just the key to start the engine....but they came in under warranty "burned out" and "melted" all the time. The only explanation was the owners "jumping" them for too long .

The weakest link in the early diesels was the flat tappet cams....those early engines required frequent oil changes (3000 miles at the most) and the correct oil (oil for HD diesels...not automotive oil....and especially NOT 10W40 oil) People, once again, used to gasoline engines, used the wrong oils and killed them... Wtih the roller lifter cams in the later engines this problem with the oil was largely avoided but the problem with the 10W40 oil sticking the rings was still there.

Regarding the one that is still running...!!!! Someone obviously treated it correctly. Nothing special to do really, just be aware that it is a light duty diesel:

NEVER USE STARTING FLUID. NEVER. NO MATTER HOW TEMPTING. NEVER.

Use the current heavy duty Delvac or Delo or Rotella oils. They are readily available in 15W40 grade at Walmart. Those are excellent oils for that engine. Too bad they weren't around in 1975.....or we wouldn't have had so much trouble.

Change the oil every 3000 miles. Contrary to a gas engine and longer change intervals the diesels put so much soot (very abrasive) into the oil that it needs to be changed constantly. Keep it fresh and it will run for a long time.

Change the coolant in the cooling system yearly and use the GM coolant supplement as the diesel could possibly seep coolant into the oil if a small seepage developed. Use the supplement to prevent any stray seepage...and change the coolant yearly to fresh, green conventional 50/50 coolant/distilled water.



The mulitvis oils of today are so much better than the multivis oils of 1970's that there is no comparison. The SE and SF 10W40 oils that ruined the diesels back then (and a lot of other engines) are history. The current SL oils for diesels are dramatically better. The VI package is fully synthetic and there is ample wear protection in the oil.. Gasoline engines should use an SL oil that is rated GF3 or GF4 (the starburst symbol on the can). You will not that the Delvac, Delo or Rotella oils are NOT GF3-4 rated. That is a good thing for diesels. The GF rating means that the oil is friction modified (among other things) and you do not need nor want that in that early diesel. Use a non-GF3-4 oil such as the Delo , Delvac or Rotella and it will be fine.


It really is a shame that the Olds diesels got such a bad rap....they were not nearly as frail as people thought if treated correctly. Slow? yes! Frugal? yes! Frail? No! Easy to kill if treated wrong? Yes!!!

It really soured people on diesels for a long time....but it made it easier on the next generation of diesels as people will certainly be better informed and the manufacturers will not take so much for granted in terms of the necessary maintenance and care. Much like the Cadillac V-8-6-4....but that is a story for another day.


BTW....use Google for a "Oldsmobile Diesel" search. There are some excellent websites devoted to the engine as there is still a strong (but small....LOL) following for them out there....people that can use them correctly and understand their shortcomings get excellent service out of them.

BTW2....you cannot convert the diesel engine itself to gas operation. Just changing the heads and such will NOT work. You would need to get a complete driveline from a scrap yard car or buy a crate engine to convert the car to gas.

There is some confusion here as some racers use the diesel block as a foundation for a really stout Olds race engine...but there are many many mods required to do this....the basic diesel engine will not just convert...you have to replace it with another engine within all practical reason for a gas "conversion"

Keep the diesel running and maintained. It will be a real conversation piece in the future and you can use the rant above as a conversation starter....LOL

BTW2....you cannot convert the diesel engine itself to gas operation. Just changing the heads and such will NOT work. You would need to get a complete driveline from a scrap yard car or buy a crate engine to convert the car to gas.

There is some confusion here as some racers use the diesel block as a foundation for a really stout Olds race engine...but there are many many mods required to do this....the basic diesel engine will not just convert...you have to replace it with another engine within all practical reason for a gas "conversion"

Keep the diesel running and maintained. It will be a real conversation piece in the future and you can use the rant above as a conversation starter....LOL
I don't have any information per se on the GM diesel engines. But having driven a Mercedes diesel for some time I agree with Bboyinski analysis of diesels. These engines are not for everyone. For example, I would not buy an old diesel Mercedes for my teen drivers because of the car's poor acceleration characteristics. I don't want my kids racing around, but if they need to quickly pass on the freeway, most diesels are a poor engine choice because it takes "planning" to execute the passing maneuver.

But if you are an experienced driver and you know how to treat a diesel "right" these engines will last forever. By design, diesel engines are inherently stronger than comparable gas engines. Fewer parts (no distributor, no plugs, etc.) mean less maintenance and fewer things to go wrong. My former Benz turbodiesel was a reliable performer, it was fairly fast for its size and weight, and it ran forever. It doesn't get much better than that...

Oh yes, one more thing, you can now use "bio disel fuel" which, in its many forms, can be obtained from recycled oil left over from the grills and kitchens of fast food restaurants. You will not only save money and help cut US dependency on OPEC oil, but your exhaust will smell like french fries...:)

wow, i found out alot today :bighead: . now i can look smart when talking to my friends about engines :D .

My parents have run diesel Mercedes forever....literally. Last year i bought a VW Jetta diesel for the wife and absolutely love that car. It is so peppy that you don't even know it is a diesel and gets 50mpg. I put a tuning box in it which basically messes with fuel amounts but does not change turbo boosts. She went from 90hp & 155lbs of torque to 115hp and 200lbs of torque. She will run 16's in the 1/4 mile and NO smoke. Few friends run Veggie oil in their cars, little bit more to it than dumping it in your tank. They will make you hungry for McDonalds if you drive behind one. Go to www.tdiclub.com (http://www.tdiclub.com) and you will learn a mess of deisel maintenence tips no matter what you drive. Oil type and change intervals are VERY imprtant in the old ones. I run Amsoil synthetic at $11/qt and go 10k between changes but don't even think about doing that with yours.

:Poke: Hi, I have a 79 Caddy Eldo with the 5.7 litre Diesel in it and it runs great and gets 29 mpg, not to mention lots of stares at the fuel pump. It has 200k miles on it and still runs great. The answer to your question of "coverting" the diesel to gas is NO. An engine with 22.5:1 compression ratio will not work with gasoline. It is a misconception that the olds 350 diesel was a gas engine converted to run on diesel. The confusion comes from the fact that they both have the same displacement and almost the same drive train and ran in what were previously gas powered cars. The two engines are totally different and cannot be converted one to the other without extensive modification and then it would not really be a simple conversion. Go to http://members.tripod.com/~A350Diesel/index-17.html
for some very interesting info on this engine and you will see that, as the previous posts alluded to, it is in fact a very robust engine. (provided you have the DX block which I am sure that year of car does). There is a link on that site to the olds 350 discussion forum which has loads of usefull info on this engine. Here is the lind for you convenience http://login.prospero.com/dir-login/index.asp?webtag=350Diesel&lgnDST=http%3A%2F%2Fforums%2Edelphiforums%2Ecom%2F 350Diesel%2Fstart
Just click on the guest link on this page if you are not a member.

Hope this provides some good information for you. You will grow to love your diesel :worship:

Bye, BCWayne

I have a 1979 Fleetwood Brougham diesel which I bought new. Drove it for about 2 years and then only a few miles now and then since. I keep thinking it might be worth something someday. Can someone tell me how many Fleetwood Broughams were made in 79? I can't imagine they made very many. Mine is 100% original and runs the same as it did out of the showroom. Yes some smoke and 25-27mpg.

total production of the fleet broghams was 42,200
diesel was a $849 option and was only avaible late in the model year for your car

unforetuneatly my book isnt breaking out prod numbers by engine ....

They aren't collectible yet. But in a few more years, if yours still runs, it could probably fetch some money...:lildevil:

Ben how has your diesel been to you?

Thanks for the info! I'll continue to house and enjoy it.

Ben how has your diesel been to you?

Fine. It's been maintained over the last 25 years and I just had it overhauled in September, so its doing a bit better than average now...;)

Glad to hear it. As time goes by the fact that you have a diesel Caddy is going to get better and better.