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Update on 85 Seville - Buy or not to Buy ???

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I want to thank everyone on this forum for the many responses I have received in ONE day regarding my car search.   Specifically, I am considering a 1985 Seville (serial numbers over 3000) as a daily driver (perhaps a commute once a week) and otherwise a weekend cruiser and garage beauty.   My concern is the HT 4100 and the fact that the Carfax indicates less than 200-300 miles on the car per year.  It's a low miler - 50K- and has the original engine.  I've learned about using 15w oil, or maybe 20w, or some say only 10w - and most seem to think the coolant tabs aren't needed.  I didn't see them at my local auto parts store, so maybe it's okay not to need them.   

I like the Seville style. My concern is not only the proper maintenance for this engine but also the fact it has been driven so lightly over the 31 years that if I begin a commute 90 miles highway round trip one morning the gaskets, as old as they are and everything else, might leak.  

The radiator and thermostat were replaced on this car in 2014.   Makes me wonder if overheating occurred, and that's a concern, too.  

I'm still considering the car.   And I'm checking the huge 77 Eldorado too.  But I'm not as excited about it as I am a Seville.   ?

Thank you for being very helpful to me. I appreciate all of you - and this forum - very much!


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Coolant tabs ARE needed!  I may be wrong but you may even find a lable on the shock tower advising their use.  

I dont know much about this engine but I think it is similar to the 4.9 having orings for the cylinder sleeves and the tabs will prevent leaks.  In addition the intake needs sealing with the tabs.

OldCadTech and KHE are familiar with this engine and can guide you in more detail.

The arguement against using the is the potential to clog the heater core or radiator.  

I would use Rotella or Delvac 10W30 in it.  

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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BBF is correct the tabs are recommended.

The local auto parts store is usually NOT going to carry them but I bet any Cadillac parts department will.

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Personally, I use them. Could the HT-4100 survive without them - YES, of course. If you decide to use them, beat them to a chunky powder while they are still i the package with a hammer before putting them in the LOWER RADIATOR hose or if the T-stat is out you can pour them into the engine.

BBF is also correct, they do have the potential to clog a radiator or heater core in cooling systems that have received less than proper maintenance and are starting to restrict flow.

I would classify the 85 Seville in that category because of the time it has been sitting and do a coolant machine "Power Flush" with a cleaner. 

Warning: Be careful who you have do a cooling system power flush! This is a BIG rip-off "service" if not done correctly so pick your technician/mechanic wisely.


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