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engine swap on '98 sls. with a '95 engine!? Help please


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I have a 1998 seville sls and the head gaskets are blown..?(see below) It overheats extremely fast and I decided I should just get a new engine rather than redoing the head gaskets because it has overheated so many times I figured something is wrong(head cracked?). I do not know much about cadillacs and need some help. I found a northstar engine out of a '95. Will it bolt up and also will the ecu be a problem since its a diff. year? any info helps.

I am not 100 percent sure the headgaskets are blown, but almost certain. It over heats extrememly fast and also blows white exhaust smoke. Thats what makes me think it is. Also smells like coolant under the hood and also steam/smoke will come from the hood which smells like coolant. Also when it is at running temp. and the car is at idle or low rpm it will stall, and not just instantly but will almost studder and then die.. not sure what the problem is but is it because the head and the block are spaced out becuase of the head bolts seperated and loses compression? What are some things I can do to make sure its the head gasket?

I know thats alot, but anything will help me. Thank you very much!

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No, it will not work, totally different engine controls.

Someone will stop by and tell you what years you can use, also, you can NOT use an ETC, STS or Concours Engine from ANY year, you need the 275 hp version

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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No, it will not work, totally different engine controls.

Someone will stop by and tell you what years you can use, also, you can NOT use an ETC, STS or Concours Engine from ANY year, you need the 275 hp version

Thank you very much. Also can you tell me more about how to tell if it is the head gasket?

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Thank you very much. Also can you tell me more about how to tell if it is the head gasket?

NAPA has a "coolant test kit" that sniffs for combustion by-products in your cooling system.

That test "might" be worth doing in your situation. However, keep an open mind that your symptoms are not always the result of head gasket failure.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Thank you very much. Also can you tell me more about how to tell if it is the head gasket?

NAPA has a "coolant test kit" that sniffs for combustion by-products in your cooling system.

That test "might" be worth doing in your situation. However, keep an open mind that your symptoms are not always the result of head gasket failure.

What else would it be besides the head gasket?

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What else would it be besides the head gasket?

There are several possibilities 'besides the head gasket'. And a thorough diagnosis is not possible at the distance of the internet.

In Post #1, you mentioned a "coolant smell under the hood". That would indicate an external coolant leak and not related to head gaskets. Locate the external leak and repair.

Confirm that your air purge line (rubber hose attached to the top of your coolant reservoir) is flowing coolant properly.

Confirm that your coolant pressure cap (on the coolant reservoir) is operating properly.

Confirm that your coolant mixture is 50/50 (DexCool) ethylene glycol/water ratio.

And you do not want the heartache of mixing and matching powertrains between STS models/SLS models because of the difference in valve timing and final drive gear ratios. And that's before you address the issue of PCM programming.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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What else would it be besides the head gasket?

There are several possibilities 'besides the head gasket'. And a thorough diagnosis is not possible at the distance of the internet.

In Post #1, you mentioned a "coolant smell under the hood". That would indicate an external coolant leak and not related to head gaskets. Locate the external leak and repair.

Confirm that your air purge line (rubber hose attached to the top of your coolant reservoir) is flowing coolant properly.

Confirm that your coolant pressure cap (on the coolant reservoir) is operating properly.

Confirm that your coolant mixture is 50/50 (DexCool) ethylene glycol/water ratio.

And you do not want the heartache of mixing and matching powertrains between STS models/SLS models because of the difference in valve timing and final drive gear ratios. And that's before you address the issue of PCM programming.

So a 98 engine out of a sts will not work with a 98 sls?

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So a 98 engine out of a sts will not work with a 98 sls?

The engine, transmission, and PCM need to match. So if you pull all three from the STS that works.

If you take the heads from the SLS and the base engine from the STS that would work, but I suppose you are trying to avoid opening the engine is why you are swapping?

Bruce

2023 Cadillac CT4-V Blackwing

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So a 98 engine out of a sts will not work with a 98 sls?

The engine, transmission, and PCM need to match. So if you pull all three from the STS that works.

If you take the heads from the SLS and the base engine from the STS that would work, but I suppose you are trying to avoid opening the engine is why you are swapping?

Interesting Bruce, I had not considered that thought, that replacing the PCM would fix all incompatibilities. One thing however, he would need to change the TRANNY also, as the gear ratio is different.

So, if I wanted to make my Deville a Concours, I would change the PCM, Engine and Tranny to the 300 HP version?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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So a 98 engine out of a sts will not work with a 98 sls?

The engine, transmission, and PCM need to match. So if you pull all three from the STS that works.

If you take the heads from the SLS and the base engine from the STS that would work, but I suppose you are trying to avoid opening the engine is why you are swapping?

Interesting Bruce, I had not considered that thought, that replacing the PCM would fix all incompatibilities. One thing however, he would need to change the TRANNY also, as the gear ratio is different.

So, if I wanted to make my Deville a Concours, I would change the PCM, Engine and Tranny to the 300 HP version?

Thank you guys for all your help.. I found a 98 sts engine with tranny and also found a pcm for cheap.

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To summarize, the main differences between a STS and SLS of the same year are the engine cams, PCM calibration (not the PCM itself, but the programming), and the transmission final drive.

SO, if you want to keep the SLS transmission and PCM you need to use the SLS heads and the STS bottom end (rest of the engine).

Alternately you could use the STS engine, transmission, and PCM in the SLS, which would then have the complete STS powertrain.

Mike, if you swapped a Concours PCM, Engine, and Tranny to your car then you'd have a Concours powertrain sure. Might be easier to just swap your license tags over to the Concours lol.

Bruce

2023 Cadillac CT4-V Blackwing

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Hope that someone can correct me if I am misinformed, but I read somewhere that the PCM is programmed with VIN data which can be written only once.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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