I just picked up, yesterday, a '78 F100 with the 300 I6. First off it runs fantastic and starts as new but there is a ridiculous amount of oil leaking out of it. So much oil that I don't even know where to start because it is everywhere. It looks like someone got carried away with the Permatex trying to seal all of the engine gaskets from the outside (like that ever works). I know that the oil pan/valve cover gaskets will be a good start and need fixed regardless but I'm just wondering if there are any other common issues with these engines (front/rear seals, timing chain cover, ????). I'm quite familiar with the 289/302/390.....but the "quirks" of a 300 are unknown to me.

Once I get a chance to dig in I'm sure I'll be able to dry this thing up but was just looking for some tips on where to start. To give you an idea.....after driving it from the Pittsburg area where I bought it to the Cleveland, Ohio area and leaving it in the barn overnight I have plenty of oil drip marks under the rear bumper. Ugh! :-)

 

Welcome to the forum, Incubus2432!

Begin by giving the engine a thorough cleaning... then you can see where the oil is leaking. My best guess is the valve cover gasket. There or the lifter / pushrods cover on the side behind the distributor.

It is not at all uncommon to find the bolts loose or just finger tight. Do not over tighten them!

Good luck!

 

Also, oil pan gasket, rear main seal and timing gear cover...there are no timing chains on a 240/300. Transmission and rear end seals can also wear out.

 

Agreed on the above. Clean the engine up, get all the permatex off of it, and then just replace the valve cover and push rod cover gaskets. They're about $20 - $30 for the pair, they're super easy to replace, and at that age are nearly guaranteed to be leaking anyway. If you have oil on the sides of the engine, that's most likely where it's coming from. If nothing else, you know they're all sealed up, and you'll get a nice peek at the valve train to see how it's doing. Give them a light coat of black RTV before installing them, and as said, don't overtighten. Both are measured in in/lbs of torque to install.

If you still have oil leaks after that, then look into the oil pan, timing cover, and possibly the rear main seal. Those are a bit more involved, so try the first two, since they really only require getting a few externals out of the way.

 

On top of what the others have said also make sure your PCV valve is in good working condition. If it's plugged up it can build up pressure and push oil past every seal and gasket. Don't ask me how I know.

 

"I'm just wondering if there are any other common issues with these engines..... the "quirks" of a 300 are unknown to me."

I've got 180,000 one-owner miles. No quirks inherent to the engine.
Everything around the engine has been replaced, but internally......havent even removed the valve cover!!
Of course...Maintenance is my middle name.

Steve

 

Thanks everybody!

I picked up the oil pan, valve cover and lifter cover gaskets today so I'm gonna go with all three. There is so much Permatex (orange) smeared around the oil pan that I can't imagine that's not an issue. The oil pan looks pretty straight forward so I might as well jump right in.Thanks for the heads up on the "lifter cover"......never even heard of such a thing. :-)

I doubt it's the rear main since the clutch it working fine. Also.....the oil being deposited all over the truck underside doesn't stink like used gear oil does so I believe the rear/front diffs and tranny aren't major contributors either. Once I get these gaskets checked I'll see what I'm dealing with. Thanks as well for the PVC tip....I'll be swapping it out anyway as part of the tune-up and filter changes I usually do when I get a "new" vehicle.

It's good to hear that there aren't any inherent weak points with the 300. I had heard they were great motors before but I was always more of a v8 aficionado. I'm a maintenance freak as well so the truck will be well cared for from now on. My concern is what was done prior to my ownership......hopefully at least the oil was changed regularly.

 

If I were you, I'd look into upgrading your oil pan to the 1 piece rubber gasket. Get an 89+ gasket (a little more expensive, but worth it), and then take your oil pan and grind all of the little ridges around the bolt holes down flat. That's all it takes.
The 1 piece is vastly superior to the 4 piece older cork / rubber gasket and you'll be glad you went the extra mile.

 

X2 with what AbandonedBronco said!

 

Good tip......thanks!

 

So I pulled the oil pan today. It wasn't too big of a deal and only took me a few hours including some cleaning to lessen my grief. A few questions......

I haven't cleaned the pan rails yet but I don't see anything to grind like mentioned above. Is this a later era pan?
The dipstick was, obviously, caked/packed with silicone. A simple o-ring should do, correct?
I know I have to flatten the rails since it's deformed from overtightening but any other tips?

 

Wow! Someone loves their silicone! Hopefully none of that broke loose and got in the oil passages somewhere. Be sure to clean out the oil pump screen really well.
Nice work on getting the oil pan off. That's usually the hard part.





Here's the ridges around my bolt holes ground down flush. The older style oil pan uses those ridges to seal around the holes. The 1 piece 89+ era gasket has its own compression rings built into the gasket, so you don't need the ridges anymore.

Not sure on the o-ring. I don't think my dipstick has one, unless it's up in the handle. Usually, if oil is coming out of the dipstick, it has more to do with a bad PCV valve.


Only torque the oil pan bolts to spec. It won't feel like they're getting nice and tight, so it can be tempting to crush down. All you do is destroy the gasket.

 

Thanks for the reply and the pics. I was picturing something else when "ridges" were mentioned. That'll be quick work with the grinder. I have an inch-pound torque wrench so overtightening won't be a problem. I think while the pan is off I may change the rear main as well.

As far as pulling the pan I was surprised how easy it was after reading the write up on this site. They talked about unbolting the mounts and jacking up the motor for clearance. Musta been a different year 'cause mine dropped right out with no problem. I'm off again in a few days so I'll clean everything up, grind and reassemble then it's off to the valve cover and pushrod cover gaskets which should be a breeze.

Thanks again!

 

Interesting, is it lifted? 2WD?
I've done the oil pan on both of mine, and sometimes I wonder if it's just less hassle to remove the engine than to try to mess with unbolting everything, jacking it up, reaching around the axle, etc. It's a pain on mine!

Glad the pics helped. That's all the ridges are. They're a cinch with a grinder. Usually about 10 minutes.

With the rear main taken care of, you shouldn't have any leaks to worry about for a while!

 

It's 4wd. If it has a lift and how much I have no idea. I guess I thought a lift wouldn't make a difference with engine/frame issues. I'm more accustomed to working on muscle cars so having any clearance is something I won't question.

The main should be pretty straight forward but I gotta do a quick search before committing. Thanks again.