Community Forums

ralphl · 08-23-2016, 03:33 PM

I have a 2005 National Dolphin 5342, 34 ft, with 8.1 liter engine. It burns oil in (as far as I can tell) one cylinder only--cylinder 7 at the back end of the left bank. That cylinder fouls the spark plug in only a thousand miles. All other spark plugs are very clean. It burns about 1 quart per thousand miles. At 7.3 mi/gal that gives a quart of oil for every 137 gallons of gas. That's better than GMs acceptable oil burning of 1 quart for every 100 gallons of gas. I have the following questions:

1. Has anybody else ever experienced excessive oil burning in one cylinder only???

2. With all that oil going through 1 cylinder, is it carboning up the valves and cylinder head such that sometime far from home the valves won't close, hence get burned and the engine will strand me. Any thought????

3. With that much oil going into the left catalytic converter, will it foul it and I won't be able to pass California emissions test and have to put in new cat at $1400 plus installation costs. Usually when an engine burns that much oil it goes through multiple cylinders and both cats. Thus each cat gets only half the amount of contamination I am putting on the left cat only.

4. Most people I talk to think it is an oil ring problem, but could it be the valve guide seals. I could probably replace valve guide seals myself (although I worry about dropping a valve in the cylinder). Anybody think its worthwhile for me to replace the valve guide seals?? Has anybody had this much oil poured though a a valve guide seal? It would really have to be a bad seal to let this much oil through.

5. Corporate Bulletin Number 10-06-01-008C (SilveradoSierra.com â€¢ spark plug replacement / carbon buildup : Vortec 5300 5.3L V8) describes a new valve cover for some more recent GM engines (not the 8.1 liter). It has a baffle to direct oil spray away from cylinders 1 and 7 (the end cylinders on the left bank). Apparently it was spraying so much oil on the cylinders 1 and 7 valves that the valve guide seals let it leak through. My problem cylinder is cylinder 7, so that could be happening. Has anybody ever heard of a new valve cover with baffles for the 8.1 liter???

I'd really appreciate any input people can give me. One mechanic I talked to wants to replace the engine for $10,000!!!! You can see why I am looking for input.

BFlinn181 · 08-23-2016, 04:26 PM

The lowest cost fix is to do the valve seals. I've done it with a spark plug I broke the porcelain center out and replaced with a small pipe nipple. The pipe nipple allowed me to screw on an air fitting. Inserted in the cylinder I was working on, an air compressor pressurized the cylinder and kept the valves closed while changing out the seals.

If the valve seals don't cure the problem, next would be to remove the head and pull the oil pan and pull the cap off the connecting rod and push the piston out the cylinder.
---A much more complicated procedure, but still less than a $10,000 engine job.

twinboat · 08-23-2016, 05:32 PM

Do a compression test first. If all in range, then look at the valve guide seals.

While in there, check the oil return passages in the head. A blocked passage could fill the back of the head with oil.

keymastr · 08-23-2016, 05:41 PM

A leakdown test can tell you more than a compression test alone.

MoCoTom · 08-23-2016, 06:24 PM

Quote:

Originally Posted by keymastr

A leakdown test can tell you more than a compression test alone.

I would do a compression test first, and if it tests low then do the leakdown test. It will tell you what engine component is suspect.

Full-Timers · 08-23-2016, 09:24 PM

If that much oil was leaking past the valve guide you would see it when first starting and taking off from a stop. There would be blue smoke from the exhaust.

dieselclacker · 08-24-2016, 07:21 AM

8.1 engines in are known to use some oil. My motorhome, which I purchased new, uses a quart every 20/25 hundred miles. I would bet that ALL the oil being consumed isn't being done by the #7 cylinder alone. As suggested above, make sure the oil drain back passages in the head are open and not allowing oil to pool. Have a leakdown test done on the suspected cyinder. Valve guides checked for wear,and valve stem seals replaced.i

PJStough · 08-24-2016, 07:52 AM

My thought is that if it is using enough oil to foul a plug that quickly, you would see a lot of blue smoke from the exhaust on that side. My question would be is the #7 spark plug firing at all?

ralphl · 08-24-2016, 12:37 PM

Thanks for all the responses. I plan on doing some of the tests you mention. One thing I didn't mention is that after letting the MH sit for an hour, I had my wife start it up (and rev it up immediately) and I looked for smoke on the left exhaust. I had a little white smoke, but no blue smoke.

BFlynn181: When changing valve guide seals, what psi did you use in the cylinder, and where did you place the piston in the cylinder. I read one place that I should have the piston at top dead center of the power stroke so that if I lost a valve it would be stopped by the piston. I read another place that the piston should be bottom dead center of power stroke so that engine wouldn't rotate when I pressurize the cylinder. What piston position did you use and what psi?? Did the engine rotate, when you pressurized the cylinder?? Did you put a wrench on the front nut on the crankshaft to try to prevent engine rotation??

BFlinn181 · 08-24-2016, 12:52 PM

I think it was about 30 psi. It was a manual transmission so I just left it in gear. Having the piston up prevents valves from dropping too far into the cylinder if you do lose air pressure. A large wrench on the crankshaft pulley or a screwdriver keyed into the flywheel gear should immobilize the engine.

Wrapped · 08-24-2016, 02:41 PM

To keep valves closed while changing valve seals,remove spark plug push small rope into hole,as much as you can get in,then rotate motor by hand until piston in that cylinder stops,valves can't fall. When done back piston down, pull rope out. Yes I'm old.

M&EM · 08-24-2016, 04:22 PM

Look for an oil leak. Maybe around the external oil cooler connections.

Crossingover · 08-24-2016, 07:57 PM

Not much help to the OP, but wonder if the PCV system is burning excessive oil quantities. I have a catch can installed on a Dodge Challenger and the volume of oil scavenged from the PCV system is surprising. Certainly keeps the intake tracts clean.

Full-Timers · 08-24-2016, 09:05 PM

Quote:

Originally Posted by ralphl

Thanks for all the responses. I plan on doing some of the tests you mention. One thing I didn't mention is that after letting the MH sit for an hour, I had my wife start it up (and rev it up immediately) and I looked for smoke on the left exhaust. I had a little white smoke, but no blue smoke.

Then it’s not a valve guide. If the valve guide is worn, when the engine sits, oil will leak past the guide into the cylinder and when you start it up you will see the blue smoke from the oil being burned.