Help me to improve and maintain this nice car

December 1, 2012 | By Richard Prince


I believe that I have just hit the jackpot with the purchase of a 1950 Cadillac Coupe de Ville that has only 14,000 miles. After buying the car I drove it home to Tennessee, a distance of 328 miles. The drive train seems to be excellent. The engine is smooth and quiet and the Hydra-Matic shifts well. The car is equipped with a two-barrel carburetor, single exhaust, power steering and hydraulic power windows, which work well. The brakes seem adequate and stop the car evenly.

I’m writing to request your help so that I don’t, through ignorance, mess up a nice car. As with any car I own, I plan to drive the Cadillac regularly and for long distances, so I would like to make the car more reliable and enjoyable by making some improvements.

Specifically, I want to change from a 6volt to a 12-volt electrical system with an alternator. I also want to add air conditioning and firm up the suspension just enough to make the car wallow less. I plan to tune the engine with new plugs, points, wires, etc., flush the radiator and block, change the thermostat, change the engine oil and filter, change the transmission fluid and filter, and change the differential fluid.

What engine oil should I use for an engine with only 14,000 miles but that is 62 years old? What problems can I expect from using today’s gasoline and what can I do about them? What transmission, differential and power steering fluids should I use?

What advice do you have for the 12volt conversion? The original wiring in the car looks good.

What advice do you have for the addition of air conditioning? Should I use a late-model GM system or an aftermarket A/C system?

The original paint and chrome are in excellent condition. Some interior work, including seat covers and carpet, are needed but the dashboard, headliner and glass are excellent.

I plan to install new weather stripping throughout the car.


When converting from 6v to 12v you need to replace all of the 6v bulbs with 12v ones. The HVAC, hydraulic window pump, and windshield wiper motors need to be replaced with 12v motors or you have to install voltage reducers in the circuits. If you do use voltage reducers make sure they are designed to handle the amperage loads your motors and other components require. Your original 6v electric gauges need a voltage reducer. Your original 6v electric clock can be converted to operate with 12V and that’s preferable to running it through a voltage reducer because that tends to make clocks inaccurate. You can buy voltage reducers and just about everything else needed to do the conversion from numerous vendors, including Ron Francis Wiring (; 800-2921940).

There are many ways you can firm up the suspension in your car. The simplest and least expensive is probably to just replace the springs and shocks with markedly stiffer new ones. A shop that specializes in springs (such as a truck chassis shop) should be able to help you with this. They can remove the old springs, measure their rate, and replace them with new springs with a higher rate. I can’t tell you how much stiffer the new springs should be because that’s ultimately a subjective call. At the other end of the spectrum, you can replace the stock suspension system with a new air suspension or coil-over setup. Either of these offers adjustable spring rate, adjustable ride height, and improved ride quality, but both are relatively expensive to buy and somewhat complicated to install, and both will require some modifications to the car’s chassis.

For the air conditioning installation, I recommend going with an aftermarket system rather than a late-model GM system for several reasons. To begin with, any late-model GM system was designed for a specific application and various parts were configured to fit and work in very specific spaces while an aftermarket system is intended to be more generic and to fit well in a lot of different cars.

As far as the engine oil and other lubricants are concerned, I am generally quite partial to full synthetics but in your case I would not use them because they will almost certainly lead to leaks because your car’s seals were not designed for synthetics. So the obvious alternative is conventional oils. I’d adhere to the viscosity recommendations in your owners or service manual and would stick with a major name brand such as Castrol, Mobil, Pennzoil, Kendall, etc.

Your hydraulic power window system may be filled with brake fluid and this is a potential problem.

Brake fluid is hygroscopic, which means it readily absorbs moisture, and this leads to corrosion over time. Also, leaking brake fluid will damage paint and promote corrosion of the car’s body and anything else it contacts. You can replace the old fluid with a different type of hydraulic oil but you’ll need to completely flush the old fluid out of the system.

The potential problems with using modern gasoline in your old Cadillac stem from the absence of certain additives intended to inhibit corrosion. For example, one function of the lead that used to be in gas was to lubricate exhaust valve seats and thus slow down their wear. Modern engines have hardened seats that don’t need the lubricating effects of lead but your car does not.

One option is to disassemble your engine and modify it internally to not need the missing additives but I recommend against this. Another option is to put an aftermarket additive package into your fuel or mix some leaded gas into the tank with each fill-up. Both of these can be somewhat expensive and a nuisance. Choice three is to run the car on modern gas and take your chances that your engine won’t experience premature wear as a result.

And finally, on the subject of replacing all of the car’s weather strips, I definitely recommend against that unless they are in very bad condition.

Exact, correct reproduction weather strips are not made for your car so you will struggle to find many if not most of the pieces.

If you do choose to replace the original pieces don’t remove them until you have the new replacement pieces in hand and then remove the originals very carefully so that you can reinstall them after you discover that the new ones don’t fit or function properly.