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  redline threshold-Johnson '83 140 V4

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Author Topic:   redline threshold-Johnson '83 140 V4
stefan posted 07-23-2004 10:09 AM ET (US)   Profile for stefan   Send Email to stefan  
I'm trying to figure out highest safest RPMs for my Johnson 1983 V-4 140HP
can't seem to find stat. in the manual
my neighbor says around 3500?
what's redline for this engine?

reason asking, was overheat alarm was going off this summer for first time-never did in colder water months(fall/Spring)
we took off thermo housing-no thermos-replaced them, H20 pump is fine.
took boat out and after about 15-20 min at 4000,(30-35 mph) alarm would go off.
let it cool down, and at 3000-3500 (25-30mph) no alarm.
so I'm guessing I was redlining at 4000 and because water temp in Gulf so much hotter in summer alarm went off, whereas at same rpm/mph in fall/spring with cooler gulf water temp I was getting away with it?

Bigshot posted 07-23-2004 10:35 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Huh? Your redline is like 5500 on that engine. You have a clog somewhere or water pump is not OK.
stefan posted 07-23-2004 12:11 PM ET (US)     Profile for stefan  Send Email to stefan     
thanks big

I was thinking redline was around 5000.
I just thought of this, I noticed as I was brining boat up to a plane, and after a few minutes, it would feel like grass was on prop. But when I backed off, no sight of grass.
could it be cavitation, that's causing the problem, then causing the overheating?

Bigshot posted 07-23-2004 12:47 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Yes...Is the bottom smooth? Is your prop hub slipping?
stefan posted 07-23-2004 12:59 PM ET (US)     Profile for stefan  Send Email to stefan     
I'll check, could you be specific, Big, as far as prop hub slipping-thanks
would putting "fins"- on solve the problem?
2manyboats posted 07-23-2004 02:17 PM ET (US)     Profile for 2manyboats  Send Email to 2manyboats     
The overheat alarm would go off on one of 110 omc motors on the 22 outrage. The water pump was pumping fine and the temp. gauges showed ok, but every time I would run hard the alarm would go off . Turned out to be a slight blockage in the water passage way near the overheat alarm sensor. The rest of the engine including the other cylinder bank where the sensor for the temp. gauge is located did not heat up. Took a trip to the shop to find the problem.

Mine were proped to turn 5500 rpm

stefan posted 07-27-2004 09:11 AM ET (US)     Profile for stefan  Send Email to stefan     
update:

me thinks aong with a couple neighbors that problem was cavitation, so I took the easy way out and bought dolefins, instead of checking to see if it was overheat alarm sensors (i already put new thermos in thinking that was the problem, and there were no thermos in there)

sure enough the fins solved the problem, no cavitation, no alarm!

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