engine maintance

[Robert Henson]

Needing advice from you diesel mechanics. We have Detroit 8v92's freshly rebuilt (cost of a small house)! What routine maintenance should I worry about. Don't assume I know the easy stuff -give me the whole scoop.

[Genesis]

First things first...

Find your airbox drain connections. If they go back to the crankcase, rip that out and dump them to a crap can (some kind of container) instead. DO NOT return your airbox drains to the crankcase - ever! Make sure your airbox drain check valves are ACCESSIBLE and clean them at EVERY oil change. Do that NOW.

Second, if you have Walker Airseps, make VERY SURE the vacuum modulators are working properly. Those are the little breathers near the valve covers. If they stick closed, you WILL pull over a lot of oil and foul the turbos.

Ok, with those two taken care of..

1. Oil changes every 100 hours or annually. NEVER put the boat up for the winter with old oil in it.

2. Gear oil changes every second main oil change or anually. Ditto on the gear oil for winterizing.

3. Check boost pressure differential at the airbox and airhorns AT LEAST annually or any time you detect an exhaust leak. If there is not AT LEAST as much boost at full power at the airbox as there is at the airhorn, you have a clogged aftercooler. REMOVE AND CLEAN IT. Its a pain to get to, but this is a MUST. Clogged aftercoolers cause high internal engine temperatures and incomplete combustion = burned valves, pistons, etc.

4. Inspect heat exchanger cores annually or any time temperature creeps. If in doubt, clean them.

5. BEWARE of exhaust leaks. They are EXTREMELY common - and damaging. If you detect one, FIX IT IMMEDIATELY. If you can smell exhaust in the engine room on a cold start, odds are there's a leak. If you ever see darkening on the raw water pipes, THERE IS A LEAK - the soot condenses first on the coldest things, which are the raw water pipes and fuel cooler. Any time you catch one, bet on having to clean the aftercooler.

6. Run the engines up at least weekly if the boat is not in active use. Best is to go for a run at cruise power for a half-hour to an hour. Acceptable is to start them at the dock, wait until the temperature gauges come off the cold pegs, then run at fast idle (1200 rpm or so) until the temperature gauges will come up no higher (about 30 minutes.) Then idle for 2-3 minutes, and shut down. DO NOT idle for the entire time, as fuel can wash down cylinder walls and cause problems.

7. If you ever detect fuel on the water at idle, find the leaking injector and replace it, or suffer a trashed hole from fuel washdown.

8. The rack and exhaust valve clearances should be checked annually or every 500 hours. If nothing is found amiss and everything is running ok, it is not necessary to do a full tune-up. But if ANYTHING is out of adjustment, do the entire job "by the numbers" - no shortcuts.

9. Coolant inhibitor levels and pH must be checked every six months, and coolant should be changed every 2 years. DO NOT use extended life coolant unless you want to replace every hose and clamp in the cooling system with constant torque clamps and special hoses (not worth it in a marine application.) NEVER run uninhibited coolant, not even for a few days. Before changing coolant every 2 years, run the Penray "online" cleaner to remove any accumulated scale. Its a good idea to replace H/E pressure caps every 2 years too - they're cheap.

10. Zincs must be checked at least every three months. Any zinc more than 1/3rd eroded should be replaced. Don't forget the ones on top of the raw water pumps, and don't forget your shaft and rudder zincs on the outside of the boat!

11. If you don't have them, install all of (a) mechanical temperature and oil pressure gauges in the engine room - and check them at least once on each trip about 30 minutes in to make sure they read with the bridge ones - hourly checks are better; (b) 195F temperature alarms on the cooling systems, (c) 210F alarms on the exhaust cans (dry; airpax makes these switches) where the water injection point is. The latter will tell you FIRST if you lose raw water flow, and is the only RELIABLE sensor that will. CHECK ALL ALARMS MONTHLY to make sure they WORK.

That's a good start.

[dshuman]

Some of the really simple items:

Read your 8V92 DD Operators Manual. Get one if you don't have it. It's full of "how it works stuff too".

Make sure you use the right oil. These are 2-cycle engines and require very specific oil that's different than the regular 4 cycle engine oil. "Delo 100" or "Detroit Diesel 2 Cycle Engine Oil" straight 40 weight is a good bet. See the thread elsewhere on this site for other's opinions.

You probably have RACOR fuel filters. If you don't and just have the engine fuel filters, add RACORs. Change them per operating hours or at least every season. If one or both engines start to run slow, even at WOT (wide open throttle), change your RACORs first since plugged fuel filters first show up as a "slow engine" well before it completely stops.

Never store your boat over winter (if you do) with used oil in the engines. Even if you only ran it 100 hours from the last oil change, change oil and filters prior to winter storage.

Last, I don't know HOW to check the Walker vacuum modulators on my Walker Airseps, like Genesis mentions. I just shake them and if they rattle, I assume they're OK.
Also, Walker makes a "crap can" air box drain that is filter ventilated so oil particles can't get into the engine room airspace to slime things up.

[Genesis]

The proper test for the vacuum limiter on the Walker system is indeed to make sure it rattles... if it doesn't, then its stuck closed!

Oil is EXTREMELY important. It MUST be Cx-II (that is, 2-stroke) rated. MOST oils are rated Cx-4 rated, but not Cx-2.

It should also be straight 40 weight. NO MULTIGRADES IN DETROIT 2-STROKES - EVER.

The big deal with oil beyond the straight 40wt is that it needs to have a sulfated ash number below 1.0%. Most 4-stroke rated oils have too high a sulfated ash number and will foul your exhaust valves.

[dshuman]

Other subject - Did 'ya get the e-mail pictures I sent you a couple weeks ago on the RIB Jet Drive Tender? Pascal somehow didn't get them when I sent them the same day.

Doug

[Genesis]

never received 'em.

Think I'm going a different direction though.....