I purchased a 78 Eldorado 4 years ago that had 18,000 miles on it. It was always garaged in a dry heated area and I think had some service attention and was driven occasionally.
I am unsure of what fluid change and flush should be done now and how often to change engine oil.
Hello, nice car you have there. I have a low mileage 70s Cadillac too, that was stored for many years. If your unsure when the last times the fluids were changed, I would just change everything. Engine oil and filter, transmission fluid and filter. I think the TH425 has a filter? I'm not an expert on FWD Caddy's. And change the differential gear oil too, that usually gets forgotten but is just as important. I believe its still called a differential on the 425. Also if the car has not been driven in awhile I would change the brake fluid in the master cylinder and bleed out the braking system with new fluid. Just as a safety precaution. Brake fluid is very cheap. My daily driver is a 1972 Coupe Deville with the 472ci. I change my oil and filter every 3,000 miles no matter what. I just use conventional 10w30. No synthetic. But I do ad the ZDDP zinc additive. I'm sure you'll get lots of other opinions here too.
Welcome to the forum!
-Gavin
What sort of plans do you have for this car? Are you going to drive it? If so how often and how far?
The 425 has a filter but it is different than the 400 as is the pan gasket. Be sure you or your shop has it in hand before you take it apart. Its an uncommon enough part these days that if there is one in stock locally there may only be one and they may not be able to find it.
The differential in these is called the final drive. Its got a fill / level check plug but no drain like most others in the era so to change it you need to pop the cover which then requires a new gasket. Its a special 2 part gasket that has a gap in one of them at the top that acts as the vent so you don't want to just goop it up with RTV.
Thanks for the comments, will try to get everything done before winter storage.
Dave