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Cadillac HT-4100 Engine

The HT-4100 (option code LT8) was an exclusively Cadillac design that mated cast-iron heads to an aluminum block. HT-4100s failed in large numbers; thousands were replaced under warranty.

Note: Starting in 1982 and continuing to 1985, the Eldorado and Seville were only equipped with the HT4100 Engine, VIN 8. There were no optional gas engines offered.

Officially called the "High Technology 4100cc Engine", it actually used some old technology from the Chevrolet Vega and even earlier "V" type engines.engines. By this time steel sleeved aluminum block engines were still not perfected as todays engines are, and they had many problems.

Also see Engine Problems.

I've heard that reports of block porosity are a myth. But GM did and does recommend the use of the cooling system supplement tablets. And the coolant MUST be changed on a bi-annual basis, regardless of mileage. Put in 2 of these pills at that time. If you decide to use an aftermarket coolant sealer such as "Bars Leak" follow their instructions.

In 1985, there was a change in the casting of the blocks for these engines--reinforcements were added. Eldorados with serial numbers after FE623772 had this new block and are sought after by knowing buyers.

All of the engines are rebuildable, but when GM remanufactured the 4.1L engine it added welded reinforcing as part of the rebuilding. It's not something most machine shops can do.

Maintenance Items

Year Timing VIN Oil Cap# Coolant S plug/Gap* Air Filt* Oil Filt* Fuel Filt*
All 15o 8 4+1 qts 16 qts RS-46SZ/.080 A329C
**V8 Cylinder and distributer diagram**

Firing order: 1-8-4-3-6-5-3-2

Distributor turns Counter-Clockwise



Year Bore Stroke Comp. Ratio Torque @/RPM H.P. @/RPM
1982 3.465 in (88.0 mm) 3.307 in (84.0 mm)