500 rpm Lost & Overheating at WOT

wildspeed · Apr 3, 2006

Hello Everyone, Took the boat out today to the Gulf and notice that the engine was not reaching 5500 RPM at WOT, but was 4900/5000. Back home I look at the engine and notice some salt deposit around the lower head. I guess the seal are leaking, what problems & fix do I have to look for. Thanks 1990 Evinrude 90HP

KYHunter2 · Apr 3, 2006

Re: 500 rpm Lost & Overheating at WOT

Look like , a bad head cover gasket or head gasket. If your losing rpm's, do a compression check . It should , tell you if you have a compression leak. Pull the plugs, if there clean . You have water intrusion. probably head gasket. Good-Luck, KYHunter

wildspeed · Apr 9, 2006

Re: 500 rpm Lost & Overheating at WOT

Thanks KYH2 Resolved the problem for the salt issue. Actually one of the rubber hose from the thermostats to the heads was leaking, spraying water on the engine. That was a no fuss fix.(but those hoses are not cheap, lol) After the fix, I ran it at WOT and the overheat buzzer came on after few minutes. I've searched and readed that it can come from the engine lugging (since I lost 500 rpm, and running 5000 rpm at WOT).The engine was not buzzing the last 3 times I took it out, even WOT was 5000 rpm also. Did running with the leaking hose could have damage something or could something be stock in the water system and made the hose blow?(starboard side) I guess my next step is to do the engine compression test (need to do a search on that). I was thinking to get a pump kit to be in the safe zone, but my water pressure at WOT is almost 30psi, so I don't think this is the problem. Can the trottle cable got out of adjustement (or other parts) and made the engine lose the 500 RPM??? (just an idea) Lot of questions and confusing thoughts, but not to sure of the next move. Thanks for any input

KYHunter2 · Apr 9, 2006

Re: 500 rpm Lost & Overheating at WOT

If it were me , Id pull both heads and head covers and thoroughly clean all passages. If water pump is more then 2 years old Id change it , and thermostats. Theres alot of things that need to be done as maintenance. Carbs rebuilt , water pump , thermo's etc. I guess its possible your adjustment could be off , not letting it get full throttle. Put shifter in full WOT throttle position, and see if advance is against its stop , etc. Its a hard thing to tell what to check, in words that you'll understand. At least for me. If you dont have a manual, get a oem specific manual for your motor . Your symptoms point to alot of possible causes . You'll just have to trouble shoot, until you can narrow it down. As far as compression test , remove all plugs, turn off key , and attach tester to plug hole . Use a jumper to jump from pos. (batt) post on solenoid to 3/8 I believe nut/post on solenoid. To crank engine.

One more thing , Id QUIT running engine until you make sure the cooling system is operating correctly. You must get your rpm's back up or you WILL be lugging your engine . Good-Luck, KYHunter

wildspeed · Apr 14, 2006

Re: 500 rpm Lost & Overheating at WOT

I do Have the manual (very helpfull since mecanic & me are 2 things) Did the compression test today, all 4 cylinders were 115/120. Check the head temperature at high idle and all of them were in the 130/135F range. I regap the plugs ( I use the SS one) at 35 instead of 30 ( after reading in multiple post that 40 was sometime better than the 30 posted in the manual). I notice that the plug where oily and had a nice black deposit, sign of richness, right ? I run 50.1 premix (VRO disconnected) Anything to adjust ? I did replaced the thermostat few month ago.(installed the SS one) I ordered a water pump kit and will be doing that next with replacing the gearcase case fluid. I also did a decarb, replaced the inline fuel filter, the water/fuel separator filter and inspected the fuel line. After that it will be time to go back to the water to see if anything good happened.

KYHunter2 · Apr 14, 2006

Re: 500 rpm Lost & Overheating at WOT

Probably running rich, or not getting a good spark. Have you done a spark test? Should jump 7/16 or so gap , bright blue , with a good snap sound. While your at it unless you've allready done it . Soak/clean carbs, blow out all passages with compressed air, and install new kits. ( very easy ). I dont remove jets, unless, carbs are really gummed up. I would do carbs ,while your working on it anyway. I dont know if your motor came with the cork floats, or not. If it has them , change to new style. The kits with floats, aren't that pricey anyway. Doing carbs can eliminate , one of the worst things, that can happen to your motor. A lean or fuel starved cylinder , is like running your car, with little or no oil. Your outboard, like your car won't last long . One other thing, when you drain/refill lower unit . Install new washers, on the upper and lower drain/fill screws. Also, if you dont know ,you fill it from bottom hole, until it comes out top one. Good-Luck, Let us know how it goes. KYHunter

wildspeed · Apr 27, 2006

Re: 500 rpm Lost & Overheating at WOT

Finally got around to check spark, everything there is good. I also synchronized the carbs . I did took apart the thermostats again to be sure everything was OK. Will replace the impeller and lower fluid this weekend and go for a test ride on Monday to see how it run. I run the engine for few minutes at 5500 rpm after runing it for 10mn at idle/3000rpm on the hose and temp was on the 140/145 range. Is it OK or to HOT?

Cricket Too · Apr 27, 2006

Re: 500 rpm Lost & Overheating at WOT

The temp is fine, just about right, but your gonna kill that thing if you keep running it above 2500 RPM on the hose, I wouldn't recommend doing that anymore. You have no load on that engine when it's on the hose.

Solittle · Apr 27, 2006

Re: 500 rpm Lost & Overheating at WOT

DON'T run that engine at engine above 2,000 rpm on the hose. as in PERIOD..

KYHunter2 · Apr 27, 2006

Re: 500 rpm Lost & Overheating at WOT

What they said ! It has to be an awefull sound, running that high rpms , on muffs ? ? I'd have to have earplugs for sure ! ! I dont reckon, you'd have to hear it, for very long. Good- Luck, KYHunter

wildspeed · May 1, 2006

Re: 500 rpm Lost & Overheating at WOT

OK, I got it, 2000 rpm Max on hose...(and yes it was loud) Check the impeller (like new) and replaced the gearcase oil (the one who came out was dark green, is that normal ?? the one I put in was yellow/orange) I finally took the boat on the water and it ran almost perfect, Idling a 700 rpm on gear (and few smoke), running 5400/5500 rpm at wot. But the alarm did buzz twice when running at wot, check temperature (with digital thermometer) on both head showing 155/160. After that, I ran it a 4500 for 15 mn and no buzzer, ran it again 10 mn at WOT and no buzzer......

Could it be a bad sensor ??? I did squezz the gaz pump when the alarm was buzzing to be sure it was not fuel starvation.

ob · May 1, 2006

Re: 500 rpm Lost & Overheating at WOT

Is this a constant and not intermittent buzzer tone?Trying to make sure that it is in fact the overheat sensor.When the buzzer sounds ,does it shut off on its own after reducing rpms?

wildspeed · May 2, 2006

Re: 500 rpm Lost & Overheating at WOT

Yes this is a constant buzz.(VRO is disconnected) And yes it will shut off on is own (min or two) if I slow down.

500 rpm Lost & Overheating at WOT

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