I just picked up a 1987 Sedan DeVille with 88,000 miles. It of course has the HT 4100 engine in it that seems to be problematic for various reasons. This one runs extremely quiet and smooth. I removed the oil filler cap and saw no signs of white gunk that might indicate coolant leakage, so I am assuming that the engine, for now, is in good condition. However, since I do not know the service history, the first things I would like to do are an oil and filter change and a coolant flush. The owners manual didn't come with it, so I need to know what is the recommended grade, type, (dino, synthetic), and quantity for a complete oil and filter change and what is the capacity and recommended type, (orange or green), of coolant to use? I know from reading this forum that I need to add the tablets to the system when I flush the coolant.
Does anyone have any other suggestions on how to prolong the life of this engine other than keeping up with the oil and coolant changes? I love the way the car rides and I intend to just fix the minor trim work that needs to be done on the interior and keep it as a Sunday driver.
Some other people might have an oil preference, I use 10w-30 in mine and you don't need synthetic as I have yet to see justify the added expense. I see a lot of the 5 qt oil jugs now on parts shelves, I usually grab one of those and an extra quate just in case. Do not overfill above the full mark. I use either a WIX or ACDelco oil filters and stay away from the cheapies, same with air filter. The regular green coolant with distilled water 50/50 mix and crushed tabs. Too much of the coolant tabs only plugs the heater core so don't always need more than 2 or 3 of the tabs. I do my coolant every 2 years. When I do the flush, I always take the coolant reservoir off and flush it with spray nozzle, clean out the hose from reservoir to radiator. Inspect your radiator cap carefully, look for cracks in the sealing surface and replace if needed.