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79 Deville 425 Engine trouble


AtlantaMc

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Hey guys,

Having trouble deciding which way to go with some engine trouble I've had lately. Recently had the rear main seal replaced on my 425 due to major oil leak. Sending unit replaced too. Still leaking, so had the valve cover gaskets replaced. Still leaking from the upper rear side of the engine is where I am now. The car was my Aunts with 85,000 miles. Problem found is she wasn't great with the oil changes allowing the insides to become gunked up and baked on. Not driven much in the last 10 years which has not helped other seals, Plan to keep it in the family and pass it down eventually, so wanting get it up and running for me to enjoy now! I guess my question is rebuilt vs new crated engine? Cadillac dealerships won't touch it. Person replacing the seals doesn't want to tackle a rebuild. It's also ideling rough and no one found yet that wil tackle the rochester carb.. I feel like I'm running around in circles at this point. Thought I'd reach out to some of you with more experience. Atlanta, GA.

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Mark McDermott

79 Deville 84,000

97 Deville 279,000 :yupi3ti:

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If you can't (or don't know how to) do part of the work yourself, it is going to be expensive either way you go.

I would check around with local shops and get prices on a complete rebuild vs a new crate engine.

If the price of the crate engine wasn't TOO MUCH more... I would probably go that way.

Remember that over and above the actual cost of the crate engine, you will still have the additional expense of having the old engine pulled and the new one installed.

Both Edelbrock and Holley used to make a replacement for the Rochester Quadrajet.

The common name for them was a spread bore.

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Thanks, Jim. Sort of leaning towards the crated engine myself. Went through that with my 97 deville too. The car was purchased at Lone Star Cadillac in Dallas off the Show Room floor. So it's from your neck of the woods and an Atlanta transplant like me... :) Thanks for the help!!

Mark McDermott

79 Deville 84,000

97 Deville 279,000 :yupi3ti:

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If your problem is sludge and the engine wear isn't too bad, all you may really need is to pull of the valve covers, intake manifold, and oil pan and clean it out. If a compression test looks good, I wouldn't go so far as an overhaul or crate engine.

The clean-out is pretty straightforward, if dirty and tedious. You will need to run large pipe-cleaner looking things down the oil drain passages from the valve covers and possible from the lifter valley, for example. I would change the oil pump while I was looking at it. Check the crank seals for wear and leaks and replace as necessary while it's easy.

Be sure and check out the rocker arms for wear. The pushrod socket, pivot, and valve depressor are lubricated by spiritual forces in many engines and if the rocker covers are filled with sludge, they can wear pretty badly; this can account for power and driveability issues, and possibly even your idle issue.

With the lifter valley cleaned out, you may be able to evaluate the major risk items with poor oil change habits, the lifters and cam lobes. If necessary, you can put in a new cam, cam chain and tensioners, and lifters and have basically a new engine, if the compression checks good.

This should give you a great engine that you can depend on for a lot less money than a full tear-down and rebuild.

I don't know if your carburetor has a "divorced choke" (thermally operated) or an electric choke. Holley makes 650 CFM carbuetors with both types of automatic choke. Here's a new electric choke model on Amazon for $465 plus tax and shipping:

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=Holley+0-9895

The "divorced choke" model is $460 on Amazon:

http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=Holley+0-6210

But I suggest that you look into rebuilding or exchanging your Rochester carburetor. Get the part number off of it and do an online search an see what you can turn up before you buy a whole new carburetor. There are scands of rebuild kits online, which means lots of people do it. Drive an hour, to people who are interested in taking a job that comes in the door, and try again. You can do it yourself in a couple of hours, not counting letting parts soak in cleaner overnight (or two nights!). Rochester publishes instructions on how to rebuild their carburetors here:

http://www.quadrajetcarburetors.com/bushingkitinstructions.html

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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The engine should not need to be replaced or rebuilt at 85,000 miles... Sounds like the carb. could use a rebuild - minor job, minimal cost and the oil leaks need to be fixed. If the rear mail is still leaking, something was not done properly on the repair or the seal surface was nicked.

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

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Kevin, thanks, what seal is left that could still be leaking? Valve covers(replaced), Rear main(replaced), oil still coming from the upper back of engine. Can't picture that one...

Mark McDermott

79 Deville 84,000

97 Deville 279,000 :yupi3ti:

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Intake manifold.

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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Kevin, thanks, what seal is left that could still be leaking? Valve covers(replaced), Rear main(replaced), oil still coming from the upper back of engine. Can't picture that one...

The intake manifold could be leaking along the "china wall". The original rubber seals are probably like stone by now and could be leaking. If you can degrease the engine and then drive the car for a few days, the leak should be easy to spot. It is also possible the valve cover gaskets are still leaking if they were not installed properly and/or the cover bolts were not torqued properly. It might not be a bad idea to obtain the torque spec (most likely in inch-pounts) and re-torque the valve cover bolts.

You might be able to spot the oil leak without degreasing the engine but I would not tear into it to fix the leak without cleaning the exterior of the engine.

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

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  • 2 weeks later...

If you can install some dye and have access to a blacklight for the oil leak. The use a rubber gasket for the intake manifold rails and it rots out. How does the engine perform off idle?

Too bad your far away, I would have no problem tackling the job.

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  • 4 months later...

I have pulled apart several big block Cadillac's 425-500 with well over 150,000 and they still had hone marks in the cylinders and were well within specs for a simple rebearing, re ring, new gaskets and put it back together, they ran very well. I love those old big block Caddy's theyre an exc engine. The 472's and 500's being my favorites. I would think that at 85,000 miles its barely broke in.

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The last reply from the original poster, AtlantaMc, was September 24, 2013. I would hope that all is resolved by now but we haven't heard.

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 months later...

Hey guys, quick update on the 79 DeVille.

Car still leaking after the third or forth time in shop last year(tried to forget); they had just replaced rear manifold seal and it blew again on the way to work the morning after picking it up, so back to the shop(still last August/September). They were redoing the manifold seal, and also informed me the new rear main seal, the other shop just replaced wasn't holding. Frustrated at that point ,,, I said for them to fix for yet another 600.00.... versus having it towed to the other shop, and do it the right way. I've spent thousands at this point and losing ground! I went to pick up after work, only to start the car and have it sound and look like a thrashing machine(engine knocking!!). They said to drive it home and see if the kinks get worked out. Next morning, I thought it was going to explode!!! So back to the shop! They took the oil pan off and informed me I had two bent push rods. I knew at this point that whomever was hot rodding or test driving it the day before testing for leaks,,, did this,,, but hey, don't tell the customer( and a great customer over the years at that!). Let him think that starting the car caused the trouble. Long story short, I limped it back to storage where it sat until this past April. A friend of mine that has old cars recommended a place near by, so I finally got the nerve up to give it another try. It's May 15th 2014, and the car has been in the service bay for 6 weeks. I just got the newly, rebuilt original engine back 04/12/14. Everything was repainted in the engine compartment while the engine was out. I had just redone the air the summer before, so that was good. I opted to have the radiator, starter, alternator and all hoses and belts replaced to hopefully get all repairs out of the way for a LONG, LONG TIME!!! :) And just have fun driving it again!!! Will post pics once it's all back together.

Mark McDermott

79 Deville 84,000

97 Deville 279,000 :yupi3ti:

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I hope (for your sake) that it is all fixed.

The 425 engine was a really good engine and would run practically forever.

I have had a couple of them...

They are also fairly simple to work on which is a big plus.

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Do you mean bent rods as in piston rods? That's what you'd see removing the oil pan. Push rods would need to have the intake removed to see.

Glad you got it fixed - Not sure what would have caused the rods to bend other than a hydrolock situation.

I liked the '77-'79 Cadillacs - the tail lights on the 1977's were one of my favorites until the 1980-1984 Cadillacs and the '85-'92 Broughams. The '77 tail lights reminded me of the 1969 model year only the '77s were slanted and the '69s were vertical and the backup lights on the '69s were directly below the tail light lens. The '78-'79 Tail lights were a refined design of the '71-'72 versions - again the '78-'79s were slanted where the '71-'72s were "bent at the middle".

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

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If it's blowing oil seals then the crankcase vent is clogged, as is the PCV.

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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If it's blowing oil seals then the crankcase vent is clogged, as is the PCV.

Exactly what I was thinking, and from the reports of sludge, a very likely scenario. Hopefully the people that did the rebuild cleaned all those parts out before reassembling.

Never underestimate the amount of a persons greed.

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