1990 90 HP Johnson Overheating

[kevinfish]

I recently bought a 17 ft alumacraft with a 1990 90 HP HP Johnson. I had the boat out a few times and keep running into teh same problem. Steady alarm sounding. I have looked intot eh alarm adn know that it is overheating. Here is the problem. There is a strong steady flow of water coming out of the engine at all times, even whent eh alarm sounds. How can I tell if it is a water pump or the themostat?

 

[HighTrim]

Re: 1990 90 HP Johnson Overheating

Does the warning happen at all RPM's or usually only at higher RPM's?

The problem is, the overheat warning and the fuel restriction are both a constant tone. Will pumping the primer bulb cause the buzzer to stop, how about backing off on the throttle?

If it is in fact overheating, you will need to look to the cooling system. If you cannot hold your hand to the water jacket for a good 3 count, it is too hot. A infrared heat gun would be best to measure the temp. When was the water pump last rebuilt? If it has been a few years, it is time. I personally do the t stats at the same time, as I like to take the time when the lu is down to flush water or compressed air up the water line to the t stat housing, then replace the t stats.

If it turns out to be a fuel restriction, I would start at the tank vent and anti syphon valve, and work out from there.

 

[kevinfish]

Re: 1990 90 HP Johnson Overheating

HighTrim,
I did check the primer bulb during one of the alarms and it did not help. The bulb was solid and the alarm continued. I do not have a lot of infomation on the boat or the motor. The persont hat I bought the boat from had cancer and died shortly after I bought the boat. I did have my hand on the water jacket to see how hot that was but I was able to hold my hand on it. It was hot but not hot enough that I had to remove my hand. If I would use the infrared heat gun, what ius the max temp that I would be looking for?

 

[kevinfish]

Re: 1990 90 HP Johnson Overheating

HighTrim,
I did forget the most important thing...thanks for your help.

 

[HighTrim]

Re: 1990 90 HP Johnson Overheating

If the motor is new to you, I would definately replace the impeller, inspecting the impeller housing and replacing if need be. Do the thermostat at the same time as well, so you can boat with confidence that you will not overheat. It also makes it easier to flush the cooling system as previously stated.

http://www.meegsonline.com/tmd/waterpump.wmv

 

[kevinfish]

Re: 1990 90 HP Johnson Overheating

Thanks HighTrim. I am taking your advice and replacing them this weekend. I have a service manual and the video I should be good to go. I will let you know how I make out. Thanks again for your help.

Kevin

 

[HighTrim]

Re: 1990 90 HP Johnson Overheating

Good luck, hope all turns out well. Before you start, dont forget you will need a can of gasket sealing compound, get the BRP brand with the brush built into the lid as well as some marine grease. You will also need the water pump kit and t stats with new gaskets.

While the lower unit is down, I like to flush the cooling system as stated above. I would also remove the prop before starting, to keep from damaging it when dropping the lower unit, and also so that you can clean up the old fishing line that will be wrapped around your prop shaft and to re grease the prop shaft splines. Also dont forget to clean out the water intake area of debris, and re grease the splines of the drive shaft before re installing.

The hardest part will be disconnecting the shift rod and dropping the lu (which will be a piece of cake with your manual). Again, hope all turns out well.

 

[reelfishin]

Re: 1990 90 HP Johnson Overheating

I used to have trouble with small shellfish in freshwater up in NE PA when I lived there years ago, I used to get tiny little white shells up in the cooling system, even past the cooling grates on my 85hp Evinrude. I could never figure out how they got in there unless they grew there.
I found a bunch of them up in the t-stat area when I overhauled that motor years later here. The motor died of a failed head gasket and overheating even though I didn't get an alarm. The cooling system got pretty well restricted after years of use but the tell tale was still strong. The block would be fairly cool to the touch, but the tell tale stream was pretty hot once I had been running awhile.

 

[emdsapmgr]

Re: 1990 90 HP Johnson Overheating

The cylinder walls or exhaust cover should read 143-150 (on the gun) at idle, after warmed up. [unless you are in really cold water] The hot horn sounds at 212 and shuts off around 175. You can have an overheat and still have water pressure, because the telltale bleed is before the thermostat. The thermostat housing is the last part in the cooling line, and if it does not flow water through to the exhaust housing, the block will over heat. If you are going to get into the thermostat housing, check the valve body. It has two pinholes (one for each thermostat) and they can easily plug up, causing an idle overheat. I'd replace the thermostats and check the nylon pressure relief valves for heat deformation.