Oil Consumption - 8V71 TI's

[kwerges]

As previously discussed, we're currently under contract on a 58' Yachtfisher with 8V71 TI's. A mechanical survey performed by the local Detroit service center last week was less than adequate (to be discussed at a later time/thread). Cold start was performed in 35 degree weather, so that wasn't a big help either. The engines took about 20 seconds to settle into a smooth idle, and smoked for about 2 minutes tapering into negligable smoke.

One comment made by the owner made me slightly nervous, especially since my previous diesels have been Cummins four-strokes. He stated that while cruising at 1200-1400 rpms, the port engine uses slightly less than 1 quart of oil every 10 hours, while the starboard engine will use just under 2 quarts in the same 10 hours. Is this even close to normal for two-strokes?

 

[Avenger]

Depends... are they burning it or leaking it?

 

[Fanfare]

Thr rule of thumb for 871Ns was that a quart per day per engine was not considered excessive. Leakage was extra.

 

[REBrueckner]

All two cycle Detroits push some oil..."burn" it... The figure you quote was just like my 8V71TI's....my original engine used more oil than the one which had a cylinder kit overhaul at the beginning of my ownership.....that is, new rings,sleeves and pistons.....

Also, As others have posted, these engines seem to use more oil when oil is at the FULL mark on the dipstick than when it's half down....Might have been MikeP who pointed that out and as soon as I read that I realized it explained what I had observed on afew occasions....I noticed that effect more at 1800 than the usual 1500 RPm I normally cruised....

I do not believe my engines would have even started in 35 degree weather...the lower compression of DD two cycle turbos generally means slower and more smoky starts epecially in cold weather. So your description is a good sign.

Did anyone stick a finger into the expansion tank to see if there is any oily residue on the underside?? Even if coolant were recently changed, someone would have to have been VERY meticulous to cover that up....

When my 8V71TI's engines were surveyed, my mechanic made the above check, looked at the oil and tranny oil, listened to the engines based on his 25 years experience,made sure the start was cold (but in August in NY) and took temp readings at WOT....not as much as I expected, but he correctly dianosed a tranny problem (he adjusted the oil pressure higher) and that the port engine would need to be disassembled to see why there was oil residue in the expansion tank.....

If the engines turn up close to rated RPM and do not overheat while run at WOT that is also an essential test. Mine turned up only about 2150RPM instead of the rated 2300 and that's the way I like it.

 

[Diver Down]

We have 8v71T's in our 58YF. The oil usage between my last two oil changes equates to: 1 qt/8.3 hrs of run time for port engine and 1 qt/10.3 hrs in the starboard engine. I have eliminated almost all leaks in both engines so this appears to be oil burned. I agree with MikeP and Rob that the oil usage appears to be greater when the engines are filled to the Full mark, rather than just leaving it at what may be a quart or so low.

 

[saltshaker]

I had 8V71N's that didn't leak or use much oil. You shouldn't have to add oil unless you are down to the add mark, which is 1 gal. I would use about 2 quarts per engine every 100 hours. My 6V92's use no oil at all. The rebuilt engine is now using a little but my mechanic said that should lessen after the first 50-100 hours.

 

[MikeP]

I have never done a strict test of oil usage but I would estimate that our 8V71ti's don't use any more than a couple of quarts in 20 hours if that. There are no leaks so that may be some of the reason for the low "consumption." As noted, I don't fill the engines above the add mark, having noted early in my 53MY/DD8V71ti experience, that if I did so the engines "used" up the oil between full and just above "add" quite rapidly.

FWIW, this was pretty common with automotive engines in the muscle car era - many would use oil very rapidly from "full" down to "add."

Turned out it was a crankshaft windage thing - Chrysler mounted a lexan oil pan on a race Hemi motor and found that at 7k RPM, the windage could create a 5 QUART(!) tornado-like cloud of oil around the spinning crank. The oil "cloud" is more easily pulled into the cylinder past the rings and just generally is pressurized to go out any available opening as vapor to the outside. Note that this is caused totally by the wind generated by the spinning crank in the crankcase; contrary to what some people think, the crankshaft does not dip into the oil supply.

Engines with well-designed windage trays didn't exhibit that same trait - or at least to a much less degree. A good windage tray will "peel" the oil cloud off the crankshaft and reduce the problem. Absent a windage tray (or even with one) the further you can keep the oil from the spinning crank, the better.

 

[JLR]

8 92 TI's recently majored burn about 2 Qts every ten hours. As has been stated, that number would appear to double if filled to the full line. Only found that out this year after owning the boat for the past 13 years.

 

[kwerges]

Thanks for the responses. The engines made 2225 and 2231 rpms (with a photo tach) at WOT under full load, so they were close to the 2300. No load rpms were 2500+. Engine temps were 178 and 184 after four minutes at WOT under way...

 

[Glory]

I don't think I would 3 or so quarts in 10 hours be a deal breaker. It's only a couple of hundred dollars in a "good " season, (more than 150 hours IMO).

As stated above many engines consume some oil. The air box plates should be pulled and the rings should be inspected.

Good luck with the YF deal.

JM

 

[kwerges]

A little more history on the boat and engines is probably in order...

Very meticulously maintained boat (money was no object). The current hour meters only show 650+/- hours. In researching and talking to the owner prior to the current owner, it was learned the hour meters were replaced with no documentation of prior hours. So, it is unknown how many total hours are on the motors.

The mechanic that performed the mechanical survey pulled the airboxes, and the pistons and rings looked good. The wear rings on the piston rings were still visible, but the mechanic didn't check the cylinder walls for cross-hatching, etc. Two of the injector rockers had a little play, and the mechanic advised they should be replaced to achieve ideal performance.

During idle, the mechanic noted a very small amount of blue smoke in the exhaust of the starboard engine. As previously stated, the cold start was hard to judge due to the cold weather. 20-25 seconds for a smooth idle, although the "hunting" wasn't extreme by any means. The engines made factory specs for no-load rpms, and 2225 and 2231 rpms under full load WOT. Temps stayed good as well.

Obviously the unknown number of hours is concerning. I was able to speak to the last three owners of the boat (1996 to present). All of the owners claimed to cruise the boat gently (1200-1400 rpms) along with the periodic warm-ups and clean-outs of the engines. All four turbos were replaced in 2006, as well as starters and alternators rebuilt as part of a preventative program prior to 3-4 month cruises.

I'll post further reference the mechanical survey once the dispute is resolved. And again, thanks for all of the feedback and responses...

 

[rsmith]

If you can get $$$ knocked off the price put it aside for a reserve and just run it. We did that with our boat and ran it for another 6000hours before we RB'd the engines.