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Whats your beef with the V8-6-4


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Love your show but when I watched your video on "Never buy a car with this engine" I was really disappointed. I have had several cars with this engine, especially my 81 Deville I drove daily for 6 years. I often find that they work fine. It's a modified 500 engine to 368ci, with simple throttle body injection, and the best transmission GM ever made the TH400 to back it. The way the cylinder deactivation worked was the same way a Lock up torque converter and overdrive worked. Instead of lock up, it would go to 6, instead of overdrive, it would go to 4, under normal conditions it would switch to 4 without 6. It's a separate box from the computer and hardly a 'computer'. And the computers in 1980 and 1981, weren't even manufactured by GM, actually they were made by Eaton and had less problems. If you didn't want the v8-6-4 feature you snip 1 wire. As long as you changed the oil and maintained the car fair, they are solid as a rock. I'm tired of YouTubers bagging on this engine, when it was the most powerful cadillac engine of the 80s until the 4.9. One thing I will note as a flaw, if you didn't change the oil but rarely, like any engine the piston rings would wear out. When the cylinders deactivated it would suck up blow by oil and burn it. But that rarely happens unless the oil wasn't changed in 5 years. Please tell me, what makes it worse than the HT4100, because I have replaced them before the car hit 50,000 miles! The 368 was dropped because of emmissions only, the HT4100 was bad, my seville is on its 3rd. Please explain or stop this misconception. It's getting thrown under the bus to much with no good explanations to those who have one (or many in my case)


4 Answers

Modern engine cylinder deactivation sucks like Scotty said.  IMO, the 700R4 is a far better transmission than the TH400.  It is still a mechanical trans, as opposed to the 4L60E and it has the over drive feature.

No, it's not. The TH400 runs in drag cars win no modifications under 400hp, and I've never had to rebuild one. The 700R4 especially when it came out in 1982 would eventually lose reverse after wear and tear. It was better than the 200R4, but if you bought a larger GMC or Chevrolet pickup for towing in the 80s you didn't get the 700R4 you got the TH400. Did you know the 1980 and 81 cadillac had a towing package? The 90-92 did not and had lower pound capacity.

@tbar1 - Whatever.


The main beef is this. If you shut cylinders off on an engine, some are running and some aren't. The thermal differences between the cold non-running cylinders and the hot running cylinders is enough to eventually warp the engines. Now your old caddy was cast. Iron doesn't have that problem, but the new ones are all cast aluminum and aluminum warps easily from thermal differences

I understand that on newer engines completely. I just know the 81 has been a mistreated child since the click bait 'times worst cars' came out. The Nicole content in the big block cad is high enough it doesn't hurt anything. The 4100 on the other hand warped if you looked at it funny.


Ask some of the many people who had that system deactivated when it started malfunctioning early in their ownership. I'm not talking about "click bait" either. I'm Scotty's age so was around when those engines came out and knew people who owned them and mechanics who worked on them. However here's a little "click bait" for members who may be too young to personally remember:

Ask? I know. All my family drove Cadillacs in the 80s-90s. I've seen every engine in them, 5.7 diesel, 4.1 V6, HT4100, I've served them all. I found the problem child 81s had wires snipped off the solenoids (most common) and wires snipped of the computer and so on. Once you read the factory service manual and revert it back to how it was, you could clip one wire from the transmission (3rd gear sensor) and you have a typical GM throttle body V8 with only typical GM problems. It was 1981, and new tech no one knew how to service. It's a GM product,, it's not perfect. Although very adaptable. If you want a carburetor on one, buy a diesel adapter for the computer, hooks right on the back of any cadillac computer from 1981-1985. Then you can keep factory cruise and not have a check engine light. I might be new to the forum, but not to these cars. My current 84 is running a modified 4.1, with 4.5 sleeves and a 6.0 throttle body so it won't throw any codes, 3rd engine and brother in law bought it new. It's a pretty simple system.

The underlying engine was certainly decent once you disabled the troublesome cylinder deactivation mechanism. As you say though when new nobody really knew how to work on them and many were hacked up. Fact is those systems were simply not ready for prime time. Typical GM using the buying public as beta-tester.

You're right, it's just a typical GM motor, it should be loved because it's the last big block in a sedan. I'm not a mechanic, just a hobbyist, I actually got involved with these cars because I was an TV-Radio-Electronic serviceman. It's just a shame that they get this running misconception when the HT4100, the V6, and the diesel were much much worse, and the 307 in the later broughams wasn't nearly as powerful. The newest car I've owned was a 97 Lasabre, I wouldn't know what to do with this new stuff, tolerances seem to be getting so tight and I like to service my own cars.


Why do you care so much about what people think about some ancient engine? It's long gone.


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