I own a 1974 Dodge Dart Swinger with at least 113000 miles on the original Slant 6 engine. With my next oil change which is soon due, I am considering using Mobil 1 Full Synthetic 10W30 for engines with over 75000 miles (which mine qualifies) and an 8 oz bottle of FR3 Friction Reducer to cap it off. I use this same oil and the FR3 in my daily driver, a 1998 Dodge Ram 1500 SLT Laramie. What are the thoughts of the group? I am the third owner. The previous owner only had it for a short time and never changed the oil. When I learned of this after my purchase, I immediately changed oil & filter using STP's brand of full synthetic oil with the same weight previously mentioned and adding a bottle of 8 oz FR3 a little later. "Goldie" runs & drives great. I want to keep her that way. She gets a lot of compliments and looks. I only want the best for her.

 

The slant six was basically indestructible when it came out...... Change the oil semi-regularly, and it would run forever.... The rest of the car wrapped around it would rust to dust before the engine gave up.

Personally, I just can't justify the expense of synthetic oil in a vehicle that old. If you don't have oil leaks now, you will with synthetic...... it will find the tiniest crack to drip out of. And the additives? They don't do enough to justify the cost...... But, that's just me.

Welcome to DF!

 

I would agree, All the seals/gaskets are 50 years old. And they were not the best when they were new.

 

Thank you for the valuable insight on the synthetic oils. I was unaware of their propensity to create or find leaks. I don't need that. So far, I have not experienced that with my Slant 6. I will stick with a good conventional 10W30 oil and filter when I change it later this month.

 

Plain old motor oil is just fine for that car. It doesn't have the tight tolerances for synthetic oil to be needed. If your oil pressure is okay, go with regular 10W-30.

A little tip for an old engine with unknown history, get a couple of large ceramic magnets at the hardware store. Put one on the oil pan next to the drain plug and tape one in place on the oil filter. Drive the car for a bit then change the oil. Remove the magnet from the pan while the oil is draining. When you put the new filter on, cut your old one open. You want to look for ferrous particles. Metal shavings from worn steel parts. The Leaning Tower of Power is pretty tough but I like to get rid of worn steel parts as soon as possible. The magnet will stick to the metal pan. It should stick to the steel filter housing but I've seen odd ball filter with aluminum housings. Magnets don't stuck there.

 

Thank you for your expertise and that great idea. I never thought about doing either of those things you mentioned with magnets. In fact, no one has ever offered up that advice before to me. Based on your and the others advice, I'll use good conventional 10W30 motor oil and a good filter (not a cheap one).

 

The magnets on oil filters is nothing new. You may opt for a rare earth drain plug also.

 

I've worked on engines that didn't even have oil filters. I've added cartridge containers with oil hoses and when the right cartridge wasn't available I've used a roll of toilet paper. I have rarely found any metal parts but when I built a 400 into a 406 (and nearly lost my drivers license) I did scavenge some ferrous metal particles on the first oil change. I used a quart of oil the first 50 miles and nothing after that until 25,000 or so miles when I sold the car.

I've had a bunch of the slant 6 engines over the years. Usually 190 and 225. I've learned the hard way that when there IS a failure, it's usually cylinder #5. I've had two where that piston exited the block. I drove both home with a LOT of smoke coming out.

One other tip, if you put a new thermostat in it, if it doesn't have a jiggle valve, drill a 1/64 hole to let air out. Also, do NOT use a Failsafe thermostat as every single one I've worked with had either locked open or locked open soon after. Once on the initial run up to operating temperature.