Transmission oil level question...

i have a Yanmar 2GMF....tranny oil is the same as engine oil  straight non detergent 30w diesel oil

evey year,  change the transmission oil....fill it to the level. (it only needs about a cup or cup and 1/2 of oil IIRC....not a lot...
I'm curious... there's a specialty oil for just about everything on the market, but how does 30w diesel oil (Rotella, et. al.) differ from Valvoline 30w conventional?  Edit: first article found seems reasonable https://www.machinerylubrication.com/Read/28576/comparing-gasoline-diesel-engine-oils-

 
Last edited by a moderator:
What Alex said. FYI, those tach apps and/or the cheapo dedicated handheld tachs will sometime trigger on specular glare from a paint chip or other reflective defect on the target. If you get nonsensically high RPM readings, you might have to black out the target to get better S/N. Electrical tape works well in a pinch if you don't want to do the permanent Krylon fix.
Seems like a widget worth having: https://www.amazon.com/HDE-Professional-Digital-Infrared-Tachometer-x/dp/B00850ZCRI - will also be trying an audio based phone app, certainly more convenient if it works, but harder to trust, IMO.

 
Last edited by a moderator:

SloopJonB

Super Anarchist
68,713
12,363
Great Wet North
Got the optical tach on the engine yesterday, made a bunch of comparison measurements and concluded that the in-console tach basically reads 10% low... 2000 on the console reads 2200 on the optical, etc.  Nameplate on the engine includes a 3400 Max RPM notation, so that would be 3090 on the console - and the above recommendations for cruising @ 75% of max (2550), would be met at 2320 on the console gauge - compared to the 1900-2000 we've been running at.

Assuming the PO followed his own recommendations, he cruised it down from NC to Jax, that's about 90 hours @ 5kts, and we've done another 20 hours around the same RPM so far.  Saving grace might be the warm-ish water?  No signs of carbon buildup blowing out on start or throttle up, so far.

Also managed to make a crude fuel consumption reading today ~20 hours cruising seems to have consumed somewhat less than 1/2 tank, hard to make accurate measurements by dipping a rope in the fuel filler line, and not sure how close to full it was when the measuring period started, but at least it's not too far from expectation when pushing a 5000kg fat, bottom painted and slightly slimy 25' @ wl hull at 5 knots.

 
Last edited by a moderator:

Zonker

Super Anarchist
9,699
5,652
Canada
That's slightly unusual. Usually the console tachs read high (probably a Yanmar tactic to protect the engine). However now that you've got it figured out don't worry about it. They are very durable engines and don't mind working hard. 

 

Moonduster

Super Anarchist
4,823
231
The tachometer is almost certainly running off the alternator's stator. As a result, it's affected by sheave ratio and belt slip plus the consideration of how many poles are on the alternator's stator. There's almost always a hole in the back of the tach that gives access to a potentiometer that adjusts the displayed RPM to account for the arrangement - it's often got some kind of rubber plug pushed in to keep it covered. Take a close look, they're easy to adjust. However, because belt slip is real and varies with load, be aware that your "RPM" may vary based on the work your alternator is doing. You won't get reliably closer than 2ish percent across a range of RPM and belt load.

 

Ishmael

52,425
12,240
Fuctifino
The tachometer is almost certainly running off the alternator's stator. As a result, it's affected by sheave ratio and belt slip plus the consideration of how many poles are on the alternator's stator. There's almost always a hole in the back of the tach that gives access to a potentiometer that adjusts the displayed RPM to account for the arrangement - it's often got some kind of rubber plug pushed in to keep it covered. Take a close look, they're easy to adjust. However, because belt slip is real and varies with load, be aware that your "RPM" may vary based on the work your alternator is doing. You won't get reliably closer than 2ish percent across a range of RPM and belt load.
Yanmars generally run the tach from an electromagnetic sensor on the flywheel. 

 

Moonduster

Super Anarchist
4,823
231
Still, the tach likely has an adjustment and one should be able to get far closer than ±10%.

 

slug zitski

Super Anarchist
6,220
1,224
worldwide
I've recently acquired an '84 Pearson 303, and I finally got around to checking the transmission oil level (it's a little obscure unless you've climbed down into the port cockpit locker...) The oil looks good - clean, viscous, like I would expect from a transmission, but... the mark on the dipstick is about 1/4" from the bottom, and the oily part of the dipstick when dipped (not screwed in) extends about 2" above that mark.

I'm assuming this is overfilled?

Should I be concerned enough to pump some oil out of the transmission?

We've run about 20 hours so far, no bad behavior. Previous owner cruised her at 1900RPM and we've been doing the same so far, 2 blade prop pushes us about 5 knots in still water/air at 1900 (in other words: 2 way average speed in the river usually works out to about 5 knots). With a waterline right around 25', hull speed should be about 6.7 knots. Not sure I want to push what appears to be a well cared for 35 year old engine with no hour meter on it just to get another 1.5 knots of speed, and also not sure if the previous owner might have been babying her to avoid some unpleasant behavior above 2000 RPM.
Hard to say

you transmission oil cooler distorts oil capacity ..dip stick reading

measure oil level engine cold , the engine running

when running your dipstick must read full
 

Marty Gingras

Mid-range Anarchist
Checking Changing the engine oil level frequently will improve fuel efficiency and lowers CO2 emission. It’s good that the engine parts are slippery because less force is needed to make them move. In this case, less fuel is consumed. On the other hand, overusing engine oil will result in friction that alters the energy efficiency of the boat engine. In addition, high-performance oil like QuickSilver 25W-40 Marine Engine Oil and Pennzoil Marine Premium Plus can reduce pollution discharge.
 

Jim in Halifax

Super Anarchist
1,671
744
Nova Scotia
Hard to say

you transmission oil cooler distorts oil capacity ..dip stick reading

measure oil level engine cold , the engine running

when running your dipstick must read full
I doubt the OP's Yanmar 2GMF has a transmission oil cooler. Not sure when the requirement for a transmission oil cooler kicks in - somewhere in the 75- 100 HP range I imagine.
 

Steam Flyer

Sophisticated Yet Humble
44,253
9,608
Eastern NC
I haven't seen anybody mention the tilt of the engine/transmission yet.
Because the engine/transmission couple to the shaft which slopes down to the stern tube, it is tilted and both engine oil and transmission levels may not read accurately on the dipstick. Usually they read high because the dipsticks are at the back of the units.

The best way to make sure is to remove... evacuate with a vacuum pumps and suction tube... all the fluid. Yes it's a PITA. Yes you should do this anyway, because we all know that previous owners are destructive pinheads who spend years trying to ruin your beautiful new boat.

Now get the specification of how much fluid your engine and trans should hold. Pour in that exact amount. Check the dipstick, either take a photo of it or some other way to make sure you will remember it as exactly as possible.

This is your new dipstick mark. Ignore the old ones, unless they are very close to your precisely measured one!
 

Marty Gingras

Mid-range Anarchist
What damage have folks seen attributable to a low-powered diesel running too much oil in its transmission? I'd think mixing air into the oil would be the most likely mechanism for damage but maybe there is insufficient venting such that leaking past seals is an issue.
 

monkphunk

New member
39
23
Too much transmission oil will damage the shift lever seal on a Hurth HBW-250/ZF25M and probably other similar Hurth/ZF transmissions. My transmission lever seal was leaky when I bought the boat, I suspect from overfilling at some point in the past.

On the plus side, it was an easy seal to replace; no need to remove the transmission, just the shift lever and cover.
 

Latest posts




Top