1998 135 Optimax overheat when coming on plane first time

[Salmonbarry]

My 1998 Optimax has recently started giving and Overheat alarm when first accelerating to on-plane. IT has done this about three times now. IT is fine running it at lower rpms for as long as I want. After It alarms, I have stopped the engine and restarted it. After that, there is no more alarm and engine temperature gauge is reading reasonable temperature. THe gauge did not seem to read high when it went into alarm either.

I recently replaced a bad air compressor and commanded the ecm to perform break-in on oil injection.

I can take emissivity temperature reading with my lazer temperature gun during tests in the driveway if that is suggested here.

Any thoughts here?

[FMP]

I've known that to happen on a 2005/06 135. Temp goes up at slow speeds before planning if maintaining speed for a few minutes. We thought it was simply the hull and aeration of the water flowing past the water pickups . Also have a look at the impeller. Alarm stops after slowing to idle or getting on plane.

[Salmonbarry]

I've known that to happen on a 2005/06 135. Temp goes up at slow speeds before planning if maintaining speed for a few minutes. We thought it was simply the hull and aeration of the water flowing past the water pickups . Also have a look at the impeller. Alarm stops after slowing to idle or getting on plane.

When it goes into alarm, it stays in alarm even when I back off on the throttle. IT goes away when I stop the engine and restart. After I restart, it does not go into alarm again.

[FMP]

What's the temp during alarm and after restart and running at the same speed again as when it first set off. Go through impeller to pisser, powerhead ever been off?

[Salmonbarry]

What's the temp during alarm and after restart and running at the same speed again as when it first set off. Go through impeller to pisser, powerhead ever been off?

I usually see the temperature around 150-160F. I've never seen the needle pointing straight up (180F). During the alarm it may have been around 160 to 170F but I'm pulling that from my memory when this happened last year. THe pissing water stream that exits the side/rear (air pump cooling water discharge if I remember correctly) is normal. exhaust cooling outlet sputters out water as it always did.

THe power hear has not been off since I owned this engine in 2001. Don't know any previous work done on it.

[Salmonbarry]

Well I had this high temperature alarm occur again during 2019 boating season. The conditions were heavy waves and first started off plowing through heavy waves at about 3/4 throttle and did not push it to get on plane. The temperature gauge went up high over 180 F but without alarm. I then stopped and idled it about 2 minutes. I then pushed it to get on plane rapidly through heavy waves. It was fine after I got on plane.

I pulled the starboard and port side thermostat and checked in a pot of water on the stove. They opened up at the proper temperature. Just as a precaution I changed the thermostats out in 2017. I also changed the water impeller in both 2012 and 2019.

Probably unrelated, I changed out a bad air compressor in 2015 and get a good telltale water flow from that.

When I bought the motor used in 2001 it had the oil injection check valves already installed per a bulletin 98-23 for this engine.

So, it seems to do this when not on plane and under heavy load.

Any ideas? Thanks.

[staylor]

I had an '02 Opti 150 that had me confused until I read the shop manual for the Opti's 2 stage cooling system. I had run Evinrudes previously which have a conventional cooling system. The Opti runs water thru the stats up to around 1800-2200 rpm or so when the bypass poppet valve opens. When the poppet opens temps drop quickly- down to 110-120 on my Opti. Your problem sounds like a clogged or stuck poppet valve that is not opening to let water bypass the stats.

If the impeller is good then you should have 1-3 psi at idle and at least 12 psi at WOT.

My Opti never ran hotter than 120-130 at WOT and if I recall the overheat alarm would kick in around 165 at 800-1000 rpm trolling speeds when the stats were clogged or the impeller was worn out. As soon as you bumper the throttle up to 1800 the temps would drop quickly and the alarm would stop. Your 1998 model is a bit different than the 2000 and later Optis but as far as I know its got the 2 stage cooling system.
Doug

[Capt.Insane-o]

Put an impeller in it every year.

[Salmonbarry]

I had an '02 Opti 150 that had me confused until I read the shop manual for the Opti's 2 stage cooling system. I had run Evinrudes previously which have a conventional cooling system. The Opti runs water thru the stats up to around 1800-2200 rpm or so when the bypass poppet valve opens. When the poppet opens temps drop quickly- down to 110-120 on my Opti. Your problem sounds like a clogged or stuck poppet valve that is not opening to let water bypass the stats.

If the impeller is good then you should have 1-3 psi at idle and at least 12 psi at WOT.

My Opti never ran hotter than 120-130 at WOT and if I recall the overheat alarm would kick in around 165 at 800-1000 rpm trolling speeds when the stats were clogged or the impeller was worn out. As soon as you bumper the throttle up to 1800 the temps would drop quickly and the alarm would stop. Your 1998 model is a bit different than the 2000 and later Optis but as far as I know its got the 2 stage cooling system.
Doug

First, Thanks for the reply Staylor. I am looking at my service manual that covers 1998 and 1999 135/150 hp Optimax. The water flow diagram does not indicate any restriction except the poppet valve (pressure activated). I would think that that opens under the higher rpms whether it is at high rpms (~4,000-4,500) while under load before getting on plane or after it gets on plane at cruise speed and at about 4,200 to 4,500 rpms.

As you said, mine runs cool at 120-130 F but all day long while trolling.
After looking more at the manual it has water pressure specifications of 1-3 psi and idle, poppet valve opening at 4-9 psi and W.O.T. pressure of 12 psi minimum. Per manual instructions a water pressure reading can be taken by cutting the compressor inlet cooling line and inserting a pressure gauge with a tee fitting. I will do that now. This should also give me feedback on my water impeller and when it is not operating properly.

[Salmonbarry]

Put an impeller in it every year.

Thanks for replying Capt.Insane-0. So I did change out my impeller in 2019 but do to my poor record keeping on what month I did that am not sure if it was before or after my last Walleye fishing trip when I had the high temperatures. I hope that it was done after that trip. I Don't like the thought of going in to pull out the poppet valve as it is behind all of the computer and ignition parts.

[XstreamVking]

Clean the water intake screen for the compressor too. (port side low on block) There's temp senders on the compressor and on the block. The computer gives an average temp on the gauge. Could be one of several reasons to show hot on the gauge.

[Salmonbarry]

Clean the water intake screen for the compressor too. (port side low on block) There's temp senders on the compressor and on the block. The computer gives an average temp on the gauge. Could be one of several reasons to show hot on the gauge.

Thank You for replying XtremeViking. My service manual indicates that the water outlet from the compressor goes directly to the tell-tale outlet on the starboard side. I watch that closely since I had replaced the air compressor ($$$$). I checked that flow after I had the last high temperature condition and it has a strong stream coming out of the tell-tale but that was after I idled down. Hard to look at that when I'm under heavy wave conditions.

Based on my service manual, the inlet to the compressor comes from the top side of the "exhaust driver plate" located between the two cylinder heads. Looking closer at the water flow diagram, there is a screen at the connector. Easy to check that screen. Since I am not going out much because of the Corona virus alerts. This will be a nice check to do so I can keep busy at home. Thanks again for your input. I did not know that the ECU averages those two temperature thermister readings.