This i got elsewhere, but it is applicable to the 4100 & 4500 engines of many Cadillacs:

Based on what we know, what we seen, what I personally have seen in 5 years of Allante ownership,
this is the premise:

The Allante 4100 engine seems to be a big improvement over the standard 4100 of the other Cadillacs.
The Allante 4500 seems to be a much improved engine over the Allante 4100.
The Allante 4100 & 4500 engines almost never post engine failures, many running 150,000 and 300,000 K miles,
still running strong.

For those of you that are facing engine issues on the other Cadillacs, do consider the Allante engines. The Allante cars are going into the salvage yards in ever increasing numbers and the engines often get scrapped by the lb.

It is not uncommon to see one sell for $100. I wasnt able to sell a HT4100 a few years ago and since I had no room for it, it went by the lb. I may soon be facing another similar decision.


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here it is:
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"The HT4100's put into the Allante's are Allante only, and were built to a higher standard, never used on the other Cadillacs. The 4100 evolved over time, beginning around 1982. They had many issues. Some of the common 4100 failures:

1. Aluminum block/steel head design led to head gasket sealing problems.

2. Porosity in Aluminum castings necessitated the use of a GM coolant supplement. If not used, internal leaking and coolant can contaminate the oil, leading to total engine failure. The milky oil sludge is nicknamed the GM Milkshake.

3. Oil pump and cam driven off of gear on the rear of the cam. The distributor gear can wear prematurely if oil return holes are not kept clear. Engine failure soon follows.

4. GM replaced many 4100 engines under warranty in the Deville, Eldo and Seville cars. Allante engines came later, in 87 and 88. The earlier failures led to design changes and improvements for the Allante HT4100.

5. Many 4100's develop a hot knock noise, never seems to get worse, and usually does not lead to engine failure, but it is still a knock. Not seen in the HT 4100.


* The Allante 4100 engine seems to be a big improvement over the standard 4100 of the other Cadillacs.

* The Allante 4500 seems to be a much improved engine over the Allante 4100.

* The Allante 4100 & 4500 engines almost never post engine failures, many running 150,000 and 300,000 miles,
still running strong.


note:
nothing written here applies to the 1993 1st gen NorthStar engines, NOTHING.

 

some of those engines are not going for $150 .. can you believe it?