Oldsmobile Diesels :: 1964 - 1990



Oldsmobile produced diesel engines in 4.3L 263 CID V-6, 260 CID V-8 and 350 CID V-8 variety. The 263 V-6 diesel was available in Cutlass Cieras and Supremes from 1982 to 1985. The V-6 diesel featured "styrofoam" "lost foam process" cast heads.

The initial 260 and 350 diesels were very bad engines as they were delivered. Definitly, one of the major problems was an uneducated public and GM's unwillingness to do anything early on. Most people didn't have clue about diesels and neither did the mechanics. Most likely that, coupled with bad fuel, and water in the fuel, and bad head bolts did them in. Engines of the first few years have everything from alternator mounts breaking, injector pumps blowing seals, to top end problems with head gaskets blowing, push rods bending, to rockers breaking. Generally the problems are with head gaskets blowing and injection pumps rusting.

According to a number of sources, the newer diesel engines were like night and day compared to the original ones. After Olds worked out the problems, many owners have 200,000 - 400,000 miles on them, and they are still going strong. The 260 diesel apparently holds up better than the 350 though.

The Olds 260 CID V-8 diesel, produced from 1979-1980, with a whopping 90hp and 170 ft/lbs of torque, it made the 2.5L "Iron Duke" motor look like a W-30 by comparison. I wonder why you never hear about buildups based on a "diesel-block 260"? Perhaps the only engine whose main journal bores were larger than the piston bores! (well, very nearly)

The 263 V-6 diesel was available in the Cutlass Ciera and Supreme from 1982 to 1985, 85 hp, 4.057" and 3.385" stroke. The V-6 Diesel was an option in the newly designed and FWD 1985 98.

An experimental diesel, reported in the pages of "Motor Trend", when Olds was in the thick of diesel development, highlighted a high-speed diesel that Olds developed, using tuned-port air induction, on a 263 CID V-6. They put it in a modified Ciera, and it bested the acceleration of the gas version by a wide margin.

Intake manifold is specific to the diesel. Cast iron and fits like any other manifold. Topped off by a crossover aluminum casting which is topped off by an air cleaner which is ducted to an intake box at the front driver side fender/header area. The manifold has a deep valley with a machined approximate 3 1/3" opening at the front for the injector pump. No distributor, but in the place of the distributor (with the same type of clamp) is the vacuum pump. A required item since it drives the oil pump. Non A/C or non cruise control equipped cars may not have the vacuum head.

The diesel mains have all the metal of a solid-web block, plus all the metal that should have gone in those windowed-main gas blocks. Pretty hefty. Good for nitrous and turbo/super charger applications. The crankshafts are supposed to be nodular.

The diesel rod is slightly shorter than the gasoline rod, for the increased ring-land necessary for a diesel, I'm assuming.

The 350 diesel block with a 425 crank and the stock bore size block (4.057") will yield a bulletproof 411 CID small block. The 350 diesel block can be safely overbored .125" without sonic testing, to make a 437 CID small block. The 350 diesel block can be bored out to 4.25" when sonic tested. With a shaved down 425 crank and a 3.975 stroke, that works out to 451 cubic inches.

The 350 diesel block cannot be bored to 403 size; you can't bore a 455 to use the 403 sized piston (4.351") either. The CID displacement and the letters "DX" appear in raised letters on both sides of the block. The block heater was installed in the driver side front freeze plug.

Diesel production continued until 1985 when all diesels were discontinued for the 1986 model year. Diesel parts were being handled by Detroit-Diesel-Allison, and not Oldsmobile. Both AC-Delco and GM Goodwrench rebuilt 350 diesel engines are available. In terms of rebuilding, try a competent diesel truck mechanic. Olds diesels were also used in Chevy trucks.

Diesel Maintenence

Simple maintenance:
They either start or don't. Change the oil & filter @ 2000 (2500 max), but usually at 1500. Change the air filter once a year unless dirty. Change the fuel filter twice per year: one change in mid winter. That's it.

Diesel has a cetane rating, usually in the 40 to 45 range. This is comparable to an octane rating. The 350 doesn't like anything under 42. Try different brands to find the one(s) that your Olds diesel likes. Never let the tank get below ½ full unless on a long trip.

The winter blend (25% kerosene) must be used during winter. This is blended at the pump. Even with this, when below 15°F, it is wise to use an additive that prevents fuel gelling, and lowers the pour point.

Diesel fuel contains parafin which will precipitate out at lower temperatures. Yes, it's wax that clogs the fuel filter and everything, and is tough, tough, tough to dissolve and work out. Never use any crap fuel, heating oil or unknowns. It's just not worth it.

Water rusts the injector pump, and besides, diesel fuel is the lubricant for the pump. Due to nature of diesel, firing any appreciable slug of water into head by injector pump, into a rotating engine, will squirt in when piston is at near top of stroke, and will definitly blow the head gasket if you are lucky (be happy that the noncompressible water did not bend a rod, the crank, streath a head bolt, etc.).

Alcohol ruins the governor vane in the injector pump. This was supposedly corrected in later years. Any additive you use must say "for diesel engines".

Is critical. To set the original timing, the pump and pump ring are lined up, and a "special tool" (chisel in a guide) is whacked, producing a line on both the pump and pump ring. Supposedly the width of the line is worth 1-2°. Use a razor blade in the chisel groove to assure line up. Reports from the street indicate that only a few degrees off will produce major problems and blown gaskets. There are also reports of increased performance, which is very tempting to some, hence many blown gaskets.

Glow plugs:
Last about forever.

Two- definitly clean terminals 4-6X per year. Use the largest diehard that will fit, but you can usually make two kids or friends happy if you feel better changing them out at 3 years.

Head Gaskets:
Did anyone know there are two different head gaskets? A standard, and a 0.010" over (thicker) for engines that had their decks milled. With an engine at 22.5:1 compression ratio, this makes a big difference. You can imagine the interference on a decked engine with a standard thickness gasket, BUT the final critical compression would be incorrect, so a loss of performance would be experienced with 0.010" thicker head gasket on an un-decked engine.

Block Dowel Pins
Olds sent out many relacement blocks with dowel pins in the deck that stuck up too high! Olds issued a Tech Service Bulletin about the problem. So, you should check this when doing any head work. Put the head on naked (no gasket), and poke around with a 0.001/0.002" feeler guage, and if it slips around, grind the dowel pins a bit and recheck.

Compression Test
Don't "squirt oil into the cylinder to check the rings on a diesel!! The cylinder is hot enough at ½ compression stroke to ignite the oil - with potentially damaging results. You must use a diesel compression guage to accomodate the higher pressures and threads of the glow plug.

Crankcase Pressure
Olds replaced a number of engines where the crankcase pressure was up to 3½" W.G., which met criteria for new engine courtesy of Oldsmobile. To test this, you need a guage that measures inches of water. These are available at any heating supply store in the tool rack (~$30). To test, run the engine, hook up to dipstick tube, and measure the pressure.

Decent fuel economy:
18.5 around town, 25 on the road, not taking it easy, 4000 lb car loaded with extras and baggage.

Gasoline is ~118,000 BTU/gallon. Diesel is ~140,000 BTU/gallon. With all other items to the side, (efficiency, burning rate, etc), diesel has more power per gallon than gasoline. Reportedly, the precombustion chamber's swirling and mixing properties are the key to the diesel's economy.

When a diesel goes into the compression stroke, and at near TDC, the air is compressed so much that it is hot enough to ignite the diesel fuel. In the timing sequence, the injector squirts (at 1,200-1,800 psi) the diesel fuel into a preignition chamber where it ignites and results in power.

Clean fuel, clean oil, clean filter, life is usually OK.

[ Thanks to Bob Barry, Joe Padavano, Steve Ochs, Greg Pruett, Tom Lentz, Kevin Wong, Lloyd, Paul Hartlieb, Thomas Martin, Kevin O'Brien for this information ]