? for the engine experts

OntarioVanMan · Jun 20, 2004

ok heres the deal:
it's a 318.. 7 cylinders read 150 on compression test which is bang on like new BUT 1 was 75 and after tune-up was tested again it came up to around 95. What happened was I had a bad plug and it washed out the cylinder sooo the shop says they'd HIGHLY recommend changing the WHOLE engine IF and WHEN the time comes. I asked about just changing the bad cylinder. Has over 300,000 miles on it. I can't feel the bad cylinder yet and plan on running it till it pops BUT when it does:
Should I do just do the bad one or get a new motor?
or should I base the answer on the final mileage when it does go?

D Green · Jun 20, 2004

I don't think the shop is steering you wrong on the replacement. To replace one cylinder (piston/rings, rod bearing) you must remove the head, there-by weakening the remaining three cylinders on that bank. The labor for this would be almost the same as a complete rebuild. As long as it runs well, & you don't notice a significant loss of power, little oil burning, I'd drive it until it noticably needed rebuilding.

One thing, now. Since there is a loss of compression (poor ring seal) in that cylinder, your PM's become much more important, as the blow-by from that cylinder collects in the oil pan, diluting the oil's lubrication/viscosity. Using Lucas/STP type oil additives can help, as long as your weather permits the added viscosity.

I've run several engines with one cylinder low on compression, & not really had any problems.

OntarioVanMan · Jun 20, 2004

Thank You Mr Green.

It's not burning any more oil then I can notice as I use a quart about every 3000-3500 mile naturally. So you're saying I should be more prompt about my oil changes? I suppose I am getting gas in my oil when it seeps in thru the ring? Therefore reducing viscosity.

Being in Canada I couldn't really use the additive in winter but could get away with it in summer as now.

My fuel injector o-rings are leaking again and that I know is causing some of my rough idling and slow take offs. I have to feather the pedal to get power up sometimes especially when the engine is hot and I stop at a rest area and try to go quickly seems to be not getting enough fuel.

RichM · Jun 20, 2004

Just Curious,how many miles are on the engine.You said it was a 318,must be a Chrysler product?? Burnt valves that leak can also cause compression problems.

OntarioVanMan · Jun 20, 2004

yup..Dodge Ram 2500 3/4T 1999 513,000 kms or about 307,000 of your miles.
and it's only the cylinder that had the burned plug, the engine specs at 150, 6 were 150, 1 at 145 so almost new still (not too shabby) but the one got washed out as they call it. Going to have the injector rings done this week so I'll see if it works better. By my maintenance records rings were done about 150,000 miles ago. and it didn't stutter after they were changed.

davekc · Jun 21, 2004

a rebuild or low milage replacement would be the way to go. You are at the same costs to just repair the one cylinder. Just my opinion. That motor is pretty common in the salvage yards. Might find one with low miles. Make sure the block isn't cracked ect.

D Green · Jun 24, 2004

Hate it when work calls (No I don't, work is a good thing

) But crimeny, Tucson is hot.

Reading the replies, Rich brings up a good point. I haven't run any Dodges since the mid 80's, but the high mileage 318 & 360's were prone to getting burned exhaust valves. If you listen to your exhaust, as it gets worse, you will hear the "sucking miss" there. I use Lucas Upper Cylinder Lubricant, 1 pint to a tank of gas, at each PM. I *think* it keeps my valves clean, least the ads say so...

I've always changed oil/filter on gas rigs at 3000-4000. Have found the petroleum based oils work as well as synthetics, at least in our heat here. I do bump the viscocity up to 10w40, & use a pint of Lucas Oil Treatment in the warm months, Mar-Nov. One of our 3/4t Chevy's (5.7) just turned 350k, no engine problems. I should think if you're pm'ing at around 4000, you're doing as well as possible.

And anytime we can get 300k on a gas burner, something was done right. :7

OntarioVanMan · Jun 25, 2004

Thanks Mr Green 300,000k or miles?
mines 518,000k or 306,000 miles approx.

Update works all done and van is just humming!

5 out of 8 fuel injector rings were leaking.
#1 plug was burnt out cause, too much gas post combustion This plug was changed 2 weeks ago in tune-up.

Dodge does not sell ring kits anymore! NOW the rings come with the injectors and the price has been cut in half from last year! 245$ from dealer last yr. NOW $108 with ring included, big drop eh? Glad I waited in a way to do injectors.

Before I said factory spec was 150 for compression ratio I was wrong its 175.

The great news is now that all the work is done the #1 cylinder that was at 90 2 weeks ago is now back up to 170 AND all the rest are between 170 & 175!!! GREAT!!!! also had an engine flush to get rid of gas in oil for safety sake! and timing reset. Took her out for a run and WOW!! feels like I could get another 1/2 million out of it!