Operating temp for Perkins 4-108 ???? - SailNet Community

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Old 10-10-2009
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Operating temp for Perkins 4-108 ????

My workshop manual for my Perkins 4-108 is amazingly detailed in every respect except a few crucial areas, namely -

What is the operating temp range of this engine ?
What revs should it be pulling when operating at it's most economical ?

Anyone ???
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Old 10-10-2009
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Temp: 180-190F

RPMs: depends on setup aboard your boat. About 2200-2300 RPM is right for mine (42' 27.5K lb displacement hull, 3-blade 17" Max Prop).

Bill
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Temperature around 180

I cruise at 1900 rpm around 6 knots with a 17 inch Max prop set at 14 inch pitch. 37 ft. Tayana 30000lbs displacement

FWIW....the engine is rated at 4000rpm max rating with continuous rating of 3600 built in 1985

WOT is 2300 with my current prop
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Lancelot,

30K displacement? For a Tayana 37? Normally they weigh in at 22,500lbs. What are you carrying?

Also, if you can only get 2300rpm with a wide open throttle, you're very likely to be overpropped (or over-pitched). Unless there's something seriously wrong with your 4-108.

IMHO

Bill
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Quote:
Originally Posted by btrayfors View Post
Lancelot,

30K displacement? For a Tayana 37? Normally they weigh in at 22,500lbs. What are you carrying?

Also, if you can only get 2300rpm with a wide open throttle, you're very likely to be overpropped (or over-pitched). Unless there's something seriously wrong with your 4-108.

IMHO

Bill
The design weight is 22.5 K but on the travel lift it registered at a little over 30K. Not sure how well calibrated those strain gages were, but I bet it's closer to 30 than 22.

For years my engine tach has been reading on the high side with me not knowing it until I put a photo tach on it just last month. I had adjusted the max prop years before to give me 3000 rpm at WOT on my engine tach reading, but that reading is really 2300rpm. I think that as long as I'm running the engine under load and achieving rated temperatures that no harm is done. The only penality I see is that the developed hp is less at lower rpm's. Under no load that engine will read 4000 on the engine tach. (probably around 3000rpm but did not photo tach that reading since very high revs)

Another observation is when tied at dock and in gear WOT is 2150 while underway the WOT is 2300. Based on this I would assume that if running against a current that WOT would even be higher?? Usually I'm in a narrow channel and contending with a draw bridge when contrary currents are encountered, but one of these days I'll crank it up to see is the theory holds.
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Yeah, lots of things can affect "registered" and actual rpm: dirty bottom, dirty prop, too much pitch or too big a prop, impaired engine (multiple reasons), etc.

BTW, travel lift guages are notoriously unreliable. Unless you've shipped a hell of a lot of stuff, I'd bet on the 22.5K plus gear.

So, too, are tach readings. But, if you've got the right prop for your boat, you should be seeing a lot more than 2200-2300 rpm for the 4-108 as a maximum.

Bill
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Old 10-11-2009
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My Perk 4-108 runs around 190 degs
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