Luke

1992 Allante head gasket

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Sadly, I recently totaled my 2006 DTS. Since I already had my 2008 DTS performance, I used the insurance money to buy a 1992 Allante. It only has 40k miles but I was told it needs head gaskets. The only thing I can think is it sat for so long that the gaskets just rusted out. But, there is a possibility it only needs intake gaskets. According to "the guru" back in the day, the majority of head gasket failures on HT4100's and 4.5's were misdiagnosed intake gasket leaks. 

I am going to have my mechanic tear into it next week, most likely. I've read very little about 4.9's being direct swaps with the 4.5 which is tempting but would probably rather stick with the existing engine since the Allante 4.5 has aluminum heads and has just as much power as a 4.9. 

Can anyone offer any advice? Anything specific I need to watch out for? Is there a specific brand of head gaskets I should buy that would be the most reliable and last the longest? I want to make sure and do this right the first time so it will be a reliable car. It will most likely be driven quite a bit once it's running good. 

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You have a good memory, I recall the guru saying the same.  

There is something you can do if I recall, I think the intake with throttle body from the 4.9 fits, someone else will pop in and confirm that. 


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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The Allante 4.5 had a special intake manifold that was exclusive to the Allante.  The special intake manifold is what gave it the additional HP over the 4.5 engines that were in the Devilles, Sevilles and Eldorados.  I'd bet the intake gaskets are what is bad as the 4.1/4.5/4.9 were not known for bad headgaskets.

If it were my car, I'd just repair the existing engine - much easier and you won't need to worry about solving any compatibility issues between the two engines.


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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s-l1000.jpg


CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Yes. That is what the upper intake looks like. I've heard it will fit the 4.9. Would be interesting to see what power the 4.9 would have with that intake. But I think we will repair the existing engine. Hopefully it just needs intake gaskets. But, I'm tempted to replace the head gaskets anyway to avoid problems down the line. Is this overkill? I just don't want to do the intake gaskets and then find the head gaskets are bad and have to take the intake off again. 

Edited by Luke

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You can check the coolant for combustion by-products with a test kit, or have a radiator shop do it.  If it's clear, I wouldn't pull the heads.  Even with no OHC on the 4.9, R&R the heads a big job, and Timserting the block is probably necessary.


CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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3 hours ago, Luke said:

Yes. That is what the upper intake looks like. I've heard it will fit the 4.9. Would be interesting to see what power the 4.9 would have with that intake. But I think we will repair the existing engine. Hopefully it just needs intake gaskets. But, I'm tempted to replace the head gaskets anyway to avoid problems down the line. Is this overkill? I just don't want to do the intake gaskets and then find the head gaskets are bad and have to take the intake off again. 

that must be what I am thinking of, that it fits the 4.9


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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Has anyone ever heard of the Allante DFI intake being used on a 4.5?


CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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1 hour ago, Cadillac Jim said:

Has anyone ever heard of the Allante DFI intake being used on a 4.5?

The Allante is a 4.5.  I think you meant to say the Allante intake on a 4.9.  I have not heard of anyone doing that but that doesn't mean someone hasn't tried it.

5 hours ago, Luke said:

Yes. That is what the upper intake looks like. I've heard it will fit the 4.9. Would be interesting to see what power the 4.9 would have with that intake. But I think we will repair the existing engine. Hopefully it just needs intake gaskets. But, I'm tempted to replace the head gaskets anyway to avoid problems down the line. Is this overkill? I just don't want to do the intake gaskets and then find the head gaskets are bad and have to take the intake off again. 

If it were my car, I would remove the intake, then fab up blocker plates to block off the ports on the heads, plug any coolant hoses that would have connected to the intake manifold, then pressure test the system.  If it passed, you would know the headgaskets were OK.

I assume there is coolant in the oil on the Allante?  If so, I would think you could do a combustion gas test and if it was negative, you could conclude the headgaskets were OK and it is just the intake gaskets. 


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Yeah, I meant the 4.9; I was in a hurry to leave for an errand.  I suspect that the Allante cam and intake together on a 4.9 would make about 20 to 25 more horsepower.  Some adjustment to the fuel injector capacity and the valve lift (read:  rocker arm ratio) might be needed to adjust to the 9% larger displacement and horsepower.  It's possible that the air through the intake might be high enough with the 4.9 to need a little porting there too for full advantage of the design on the 4.9.  But this always struck me as a really good idea.


CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I wish I could contribute to this thread but I know little to nothing about the Allante. I have not worked on one in at least 10 years.

End Hijack. Oh Wait

:nopicssmiley:


GM FAN FOREVER

Nice, clean, luxury= fine automobile

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