Originally Posted by Pizzazz
Bringing closure to this topic. I checked the RPMs with a laser tach ($14.99 from Amazon) and it is all according to the manual. Idle is at 900, WOT at 3,600 in neutral.
tach measures 500 at idle and 2,900 at WOT.
One way to go from here is to start replacing the sending unit, the dampening system of the tach or the entire tach. Another way is to consider upgrading the sender unit with some more modern device that can send NMEA/Wifi output.
For now, I just put a never exceed duct tape marker on the tach glass at 2,700 RPMs
Glad you got to the bottom of it! My Yanmar
tach is accurate but both my temp and oil
pressure gages are off. Temp always reads slightly into the red and oil
pressure reads about 25 when it should be higher. I also wanted to get to the bottom of my gage issues and verify all was well with my engine
so had my local diesel mechanic
measure oil pressure and I used a heat gun to determine temps were actually normal. My diesel mechanic
contacted Mack Boring to see about replacing gages or sending units and they recommended that we not bother. According to them, the Yanmar gages/sending units are notoriously inaccurate and even if we replaced either or both, they couldn't guarantee any improvement in accuracy from what we have now. That comes from the guys who sell the parts
we'd need to buy! They said to verify that pressures/temps are within spec by independent means and note what gages say, and as long as the gages keep reading close to that amount, all is well.
You mention a "never exceed" line on your tach that's less than your actual maximum. It won't hurt anything but it's not really necessary on a diesel engine
that's properly propped.