Folks - I’m looking for thoughts on how to diagnose oil on my plugs. Picture below. Here’s the back drop…

1977 F100 351M
No smoke ever
Flooded in Dec
Bad power valve, carb rebuilt in Dec
New plugs installed in January
Reman 2150 installed in January
Fuel pressure validated at 5 psi
Vac at 17-19, not rock steady, vascillates b/w 17-19
Compression at 125-145

By mid February I noticed a slight flinch; a miss at idle. Starts a little slow requiring more cranks than usual. I pulled all plugs and cleaned them. Pic shows what I’m seeing at all eight plugs.

Any thoughts? Maybe stem seal? But no smoke.

 

Have you had someone start the engine after sitting overnight while you watch the exhaust? That is what you need to do to check exhaust for bad valve seals.

Another way is dropping off a long hill with the throttle closed. In this case, you, or someone you trust, would have to be following you, as there would have to be a ton of smoke to see it in the mirror.

Another thing to check. Make sure the PCV valve is clean, good, and has good vacuum at idle, that the breather cap and hose on the other valve cover are clean and able to breathe. If the vented hose or cap are gone, and a solid oil cap is in the other valve cover, there is your problem.

You need a way for air to get into and out of the engine at the same time.

Also, let engine idle with the PCV valve out of the valve cover and the breather hose unhooked and see how much, if any, smoke is huffing out of the valve covers.

 

@yardbird set up shown below. PCV is new. Crank case vent hose not obstructed.

I’ve been watching review mirror for tonight. I will take your advice I have someone else starting to get a better up close view. I’ll post a video here for reference.

 

I got my son to crank it while I took the following video. Outside temperature was about 30°. We definitely have steam after a minute or so but no smoke to my eye.

 

Better check the valve guides for being loose
I would plan on replacing the valve stem seals
While the springs are off you can see just how loose the guides are

 

Very clean
You are a wonderful owner
If that truck came into my shop I'd be saying here is Mr. Cleans truck
It does not have too much oil in it right? 5.5 quarts?
The PCV valve rattles?
IMHO valve guides are a more common issue for oil consumption than excessive blow by is on the 351-400 C and M

 

…before I open him up, any other options to test out? The shop manual has SSD-17 (valve service) as the last stop on the line. Just want to make sure I’m not overlooking something less invasive since there is no smoke.

 

@manicmechanic007 Our replies crossed in the ether. Yes, pcv rattles, brand new. I’ll check the oil to ensure not full to the rim with Brim. As for the kind words, I’m just an OCD hack who tinkers. I’m no mechanic. I appreciate you guys greatly.

 

That is super clean and neat. I' sure the next questions are not necessary, but to be sure we check everything...

Does the PCV have good vacuum at idle? The line or inlet at the carb could be clogged. Also, I can't make out the hose from valve cover to air cleaner on the passenger side. Make sure it is open and air can flow freely through it also, including filter inside the air cleaner.

Also do the blowby test with the engine warm and PCV valve not in the valve cover.

I don't know how much you drive it, but a good 3 to 4 hour drive with some hills involved or decent hard acceleration takeoffs may help. Nothing but slow, short, easy trips can cause all sorts of things, especially oil related problems like milkshake in the valve cover/PCV system, oil fouled plugs, moisture in crankcase, ect.

 

Does it use any oil ?

 

@mark a No excessive oil use. The only leak is a minor rear seal drip that I have my eye on.

I take a lot of very short trips. Nothing very long. I haven’t heard of the term milkshake - but I get your point. I will schedule a long trip with some ethanol free fuel. :-).

PCV and hoses are clear.

Keep the ideas coming.

 

I think we may have found your problem.

 

For real? Eff. What is the rule of thumb to go by? One long trip over an hour each week? This truck has the highly specialized job of taking my kids to get ice cream and taking me to the hardware store. I prefer not to make this existence a death sentence for the engine - which is original and still runs pretty damn well.

Let’s talk proper maintenance assuming this is, in fact, me doing the damage.

1. Long trip per specified frequency?
2. Clear spark plugs every every few months?
3. Change oil more frequently?
4. Check compression 2-3 times a year?
5. Apologize for a quiet life of ice cream runs and Sunday drives?

Here’s a pic of the old man. My kids call him Minty Fresh.

 

Absolutely the problem
A lot of short trips

 

You can take all the short trips you want
Just completely warm it up about every other time or every third trip at least