We have a 1993 F-250 with a non turbo 7.3. Since we bought the truck it has done what my daughter calls the "death shake" every now and then when you start it cold. It sounds like a real deep thump thump. One of my buddies who has had these engines forever and still does, say his 6.9 does the same thing and he says its a sticky valve. Since it has done it quite intermittently and some times it even sounds more like a pop, I tend to agree with him. We also get a little white smoke on start up to which kind of follows suit. What are you guys thoughts on this and if this is the case, do you think there is some kind of additive I could put in the oil like Marvel or Slick Fifty? This engine has right at 200,000 miles, really uses no oil by 7.3 standards. No blow by

Thoughts?

V-465

 

If it's just when it starts cold then clears up, you have a dead glow plug or two.

 

I checked the glow plugs when we first got the truck and they were good. I will check them again. That was likely 8 months to a year ago.

Thanks,

 

If there are any dead GP then the engine's basically starting on the cylinders that have the good ones. Under this circumstance it will shake, shudder, and smoke for a few seconds until the other cylinders catch up.

 

I am familiar with that. But that doesn't explain the loud deep thumping. Its very audible, thats what we call the death shake, not so much the stumbling til it catches up

 

So I check all the glow plugs and they are all fine. I poured a bottle of Seafoam in the oil to see if it will clean out suspected build up and free the valves up. I will run this for or so miles, dump it change the oil with some more Seafoam and see if it helps. I read on an old post that someone poured Seafoam in the intake while it was running a half bottle at a time. The reply was, "sounds risky". Sounds risky to me too. Anyone ever done that?

V465

 

You have to worry about hydrolocking, pretty much, but it does take quite a bit to do it.
I'll admit that, in the past, I once ran a frigging garden hose(at various levels) into one of these engines at idle, trying to see if it would run better(I found I was using /way/ too much water), and while it basically choked it for a few seconds till the water was cleared out, it didn't seem to do any long-term damage to the engine.
(We ran that truck/engine for a good year after that, only giving up on it when an injector /fell apart/ while trying to remove it, and we couldn't get the bottom of it out of the head. Now it's a parts truck.)

Just thinking you might be able to pour the Seafoam into one of those spray bottles, and just spray it through the engine that way. By making it a mist, you should be able to keep any /large/ amounts from going to any one cyl, and it should be fully safe.