: Seville Swap: from 83 HT4100 to 81 368

07-27-11, 02:11 PM
Hi Guys,

I have 83 Seville with a HT4100 which in my opinion doesn't have long to live (white/gray puff of smoke).
So I'm on the lookout for a replacement but I'm in doubt what to do.

The car I have is in good condition. No rattles or such, drives and brakes straight, starts ok etc. In my point of view worthy of keeping it on the road.
(If the car was crap to begin with,I wouldnt be thinking about swapping or replacing an engine :) )

So far I have thought about getting a remanufactured HT4100 since there arent a lot of other options. But then somebody told me that a '81 368 (8-6-4) would fit as a direct swap. Now, I know that the 368 of that year is pretty bad, but if you remove the hardware of that system you would have a nice base engine.

The point is, is this true? Can you swap the HT4100 for the 368 direclty with minumum of fuss?

P.S. I live in Rotterdam, The Netherlands so any tips for junkyards to visit in the USA is not an option :)


07-27-11, 09:09 PM
Your Seville was has the same drive train as the Eldorado, Rivera, Toronado of the same years. 1979 to 1985. These cars had several engines available as options. Any of which would swap in. The HT4100 was standard in the Cadillacs after 1982. The 368 V864 was also used in early production. (I had one in a Cadillac Limousine once and it worked flawlessly) All of this series also had the 5.7L Oldsmobile Diesel as an option. This is good as the Olds Diesel used most of the hardware and mounts of the Olds gas motors of the time. This makes Olds swaps fairly easy. There was also an option of the 252 Buick V6 available in the Rivera and the Eldorado. These are fairly rare though. I think the Rivera had a Turbo option on the V6. The Rivera T Type. To do one of these conversions without a parts car with the desired engine would be difficult as there are a lot of small items required to do it right and finding all the pieces would be difficult. Eg mounts and brackets and special oil pan (Drive axle goes right through the oil pan space).
Almost any engine that used the BOP bell housing could be made to work. you could even swap in a Cadillac 472 or 500. Will bolt to the trans but will probably fry the trans!

As attractive as a conversion is, I think the most cost effective and simplest option would be to replace the original HT4100. These engines will last when taken care of. They are also silky smooth and underpowered. But they are adequate for the job and give respectable fuel economy.

I i where to pick a conversion engine it would probably be an Oldsmobile V8 (307?).

07-28-11, 03:47 PM
It was my first idea to get a parts car since there is a Dutch guy living in Texas and you can stall you parts car on his lot and if you need something, he will get it from your spare car and send it over to you.
However, I have been struggling to find an 368 V8-6-4 engine let alone a junkcar with a good engine.

So I have to agree with your idea of replacing the old engine with a new one. Of course this would need to be one who has been overhauled at least.
Other option that I have is that I know someone who has a HT4100 lying around which I can buy for not a lot and get it overhauled.
I dont have any further details on the engine but I will ask.

Thanks for the help sofar!


08-10-11, 01:12 PM
small update

I did manage to find an 368 V8-6-4 in a Eldo together with an TH325. It does need some checking since it uses quite a lot of oil apparently. Transmission is sill supposedly good but will be checked of course before installing
The "only" thing I have to do is to get it out of the Eldo and in my car somehow :cookoo:
But for that, I will be going to a workshopgarage who have done this before.

09-06-11, 09:47 AM

I have decided to go for the 368 I managed to find.Got it already out of the donorcar. Also heard it running before we got it out of the car.
I tried to get it complete as much as possible, only thing I would need is a new radiator, not sure if my current one can fit with the other engine in place.
engine will be checked this week for the oil consumption
Btw, I got the whole engine for $300....

Other question springs to mind, somebody told me that it would run even smoother with camshafts from a 80' 368
Any truth to that?

10-27-11, 03:21 PM

The 368 I pulled out of the Eldorado was too far gone. It needed a major overhaul (about $4500 worth) and that is way to much money for me.
So we are now trying to find out what exactly is wrong with the 4.1 at this moment. If its not to much trouble to fix we'll do that I think.
Other option of course is to get a remanufactured 368 and have it shipped to the Netherlands. But i'm looking at import taxes, transport etc so I'll have to do some calculation before we go down that route....

11-13-11, 01:45 PM
Well ok, this is getting stranger by the minute
Apparently I already have a 368 in my 83 Seville and somebody had the same idea I had, engine still does need an overhaul but not as much as the one I bought before. But I will be taking the alternator,startermotor, headers, inletmanifold etc along

The saga continues.......

02-01-14, 10:21 AM
Just to give an update on my last post here, the 368 EFI engine was partly rebuild at the end 2011 / beginning of 2012.
The crankshaft was rebalanced, the cylinders were rehoned,new main and connecting rod bearings., waterpump, oil pump, pistonrings, pushrods and valve seals , headgasket, camshaft and some other small bits and stuff.
At the end it came down to a lot of money but I was happy……

I do have another issue but i will start a new thread in the 368/425/472/500 section