Johnson J115PLSSB surging above 1/2 throttle

[Desertsky]

Hi folks. I bought a 2002 Crestliner 1850 Sportfish a week or so ago. I took it out for a short run to check everything at my altitude (6000ft). Boat ran great for a few minutes then the overheat light and horn came on and the engine started surging like someone was switching the ignition off and on every second. I reduced the throttle to idle and the pee stream was coming out strong. I let it idle until the overheat light went off. I then slowly increased the throttle and when I hit 1/2, the surging started again. I ran it slowly back to the dock. It ran smoothly and idles just fine. When I got home I put it on the muffs and ran it for a while. The pee stream is strong but very little water coming out the prop exhaust.. After taking the muff off, I noticed a small amount of black oil coming out of the water intake slots on the lower unit.

Any thoughts on where to start looking?

 

[sutor623]

So, that surging like the ignition being cut on and off was exactly that!! When the overheat sensor grounds out, it will throw the motor into SLOW mode, which will basically prevent you from running at open throttle with an overheating motor.

1st thing you need to do, verify that the motor is in fact overheating. The scary thing about this is if it is overheating, you are going to overheat it again by running it.

Safe approach would be to remove the lower unit, check/replace the waterpump, then remove and check/replace the thermostats and poppet valves. When the lower unit is dropped, you can run a water hose into the water line and see if the water flows in and up and back down the exhaust. This will help you check for leaks and blockages. If you do this, it will be good peace of mind, and hopefully resolve your issues.

I know you are at 6000ft, so that means fresh water, but is this a fresh or saltwater motor? Also, the jets are supposed to be changed out for altitudes that high, so I wonder what type of jetting you have.

 

[Desertsky]

Thanks for the reply. Is the protection mode supposed to remain active even after the motor has cooled? If I shut it off and restarted, would that allow greater than 1/2 throttle? The boat came from Minnesota so I assume the jetting is for sea level. It is a fresh water motor.

 

[Desertsky]

Pulled both thermostats. One is cracked so time to replace them! Is there a way to run some kind of cleaner through the water system? There is what looks like hard water buildup inside. Not bad but can affect cooling efficiency.

 

[Desertsky]

Should I use 133 degree or 143 degree thermostat?

 

[boobie]

At that altitude I'd use the 133. JMHO.

 

[sutor623]

Well there ya go desert sky. Can't get advice from a better member if you ask me.

So run the 133 thermostats.

I believe that SLOW will NOT deactivate until both of these criteria are met 1) Temp sensors aren't telling the control box and power pack that the motor is overheating 2)The key gets turned off and then turned back on.

If I were you I would test your temp sensors, overheat circuits and pull the leg and change the impeller. Chances are its 2-3 years old and needs to be changed anyways.

A good way to clean out the crud is to run the motor in a cut down 55 gallon bucket, and fill it with water and 3-4 gallons of distilled white vinegar. Let the engine get up to operating temp and let her run. This is a good time to run a can or two of seafoam through the engine to do a decarb also. You will see the scale/corrosion build up in the bucket. May have to drain the barrel and do it again. (I drill a hole in the barrel and use the plug for an aluminum boat so you can drain it easily.) After you finish that all up, run fresh water through the motor for the final clean up.

Your jetting will run rich at that elevation, so as long as you aren't fouling up plugs or doing a lot of idling, you may not even have to fool with the jets.

Three reasons you will ACTUALLY overheat at upper rpm band (I say actually because sometimes you will have a faulty overheat sensor or a short in the harness to ground.) 1) A blockage in the motor 2) A failing waterpump 3) A faulty/stuck poppet valve. My V4 has the poppet in the thermostat, not sure where your poppet valve is. It may be part of the thermostat but Im not sure.

Ill say it one more time, just because Change your waterpump impeller!!!!

 

[Desertsky]

Thanks guys! The impeller was changed last year but I am going to pull the lower unit anyhow to find out the source of the oil coming from the water inlet. I suspect it is a cracked impeller housing or bad gasket. I cannot find a listing for the poppet for this engine so it must be part of the thermostat. I have a big plastic tub that I can use to run the motor in. The engine idled very well for over 30 minutes getting back to the dock so the jetting is probably not that far off.

 

[sutor623]

Cool man. I think the jetting I'd be more concerned about is the high speed jet. But in your case, I think you are okay.

Now, if you had it jetted for higher altitudes, and ran it at sea level, that would be more cause for concern.

I wouldnt be surprised if those thermostat assemblies were also poppet valves. I know that the crossflows had an extra area for the poppet, but Im pretty sure the loopers all had em in the thermostats. But that I would wait to hear from one of the head honchos on here.

 

[Desertsky]

Well, I ran the engine on the muffs and the head with the cracked t-stat got much warmer quicly. Confirms bad T-stat. A set is on order and will be here thurs. Took both out and ran the boat around the lake for a couple of hours and no overheating. Idled for an hour or so in gear trolling for walleyes and no problem.

 

[oldboat1]

but....still better to run with replacement t.stats installed, imo. Motor will load up sooner or later from cold running, particularly trolling.

 

[sutor623]

Not to mention cold seizure from the block staying very cold and the aluminum pistons warming up much quicker due to combustion, and the fact that aluminum expands quicker than steel or cast iron. I wouldn't run it hard without stats. Personally, I wouldn't run my engine at all without them.

 

[boobie]

Aw heck, they wear out a lot faster without the stats. Us mechanics got to stay in business.:laugh: