1991 Johnson V 90 overheating at idle

[Roadking5901]

Hi, Purchased a boat with a johnson v90. Motor had an overheat on the starboard side at somepoint. Replaced the water jackets,(both sides) after breaking off most of the bolts in the mean time. Replaced the gaskets and temps sensors, scraped out the water jacket channels as best I could(motor was used in salt water). Replaced the impeller, Left the thermostats out!. Ran the engine,(in a barrel) great flow from the pisser tube. After several mins, checked the water jacket temps with an infared gun... Temps on the port side 135-155, on the starboard 190 as the warning horn was going off. Attaching a pump and hose to either water jacket(bottom), great flow thru the other side and out thru the prop, and above the anticav plate. Water from the pisser tube gets very hot when the engine is running. Any ideas? Thanks.

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

Have you done the water pump yet ?? If it is okay it could be the water deflectors in the block.

 

[Roadking5901]

Re: 1991 Johnson V 90 overheating at idle

Have you done the water pump yet ?? If it is okay it could be the water deflectors in the block.

Replaced the water pump first thing. Great flow thru the block and lots of pressure out of the pisser tube... The higher the rpm's the stronger the flow. It's strong at idle.

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

What are the temps on the top of the block with your infared gun ??

 

[Roadking5901]

Re: 1991 Johnson V 90 overheating at idle

What are the temps on the top of the block with your infared gun ??

Didn't check the top of the block, took temp reading around the spark plugs, near the water hoses at the bottom, etc. Temps on the port side were 135-155, starboard side was 190-200, temp alarm was going off... Starboard side had been over temped, paint was missing on the top of the head. This was at idle after about 5 mins of running.

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

It could be the water deflectors are swelled up blocking flow. Seen it happen.

 

[KCKracker]

Re: 1991 Johnson V 90 overheating at idle

i thought the whole point of the rubber deflectors was to block flow so it was "deflected" around the head? thats all mine do.

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

The water deflectors keep the flow going to the top of the block around the cylinders. If they're swelled up the flow can't get there.

 

[KCKracker]

Re: 1991 Johnson V 90 overheating at idle

then i am confused, loking at a open evinrude as we speak it looks like all they do is block the water so its forced around to encompass the cylinders. if they were NOT swelled up and shoved in tight they would not force water up high. seems thats the only concern would be if they were breaking up. ?

 

[KCKracker]

Re: 1991 Johnson V 90 overheating at idle

then i am confused, loking at a open evinrude as we speak it looks like all they do is block the water so its forced around to encompass the cylinders. if they were NOT swelled up and shoved in tight they would not force water up high. seems thats the only concern would be if they were breaking up. ?

View attachment 205679

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

When they get swelled up, they block off the water flow. Look at your pic again.

 

[boobie]

Re: 1991 Johnson V 90 overheating at idle

Edit......

 

[KCKracker]

Re: 1991 Johnson V 90 overheating at idle

whenever i have installed new ones they fit just as tight so this is puzzling. so is water supposed to be able to pass them and they just rattle around?

 

[Fed]

Re: 1991 Johnson V 90 overheating at idle

When they swell up part of them squeezes out of their pockets and goes across to the outside of the block.
Your arrows are going the wrong way.

 

[DargelJohn]

Re: 1991 Johnson V 90 overheating at idle

I had this same issue on my 1996 Johnson 88 SPL. Starting it cold, the right bank would overheat and the left bank would stay cold and the center plate would get hot. On the thermostat valve body (black plastic piece) there is a pin hole in the middle of the body. This pin hole lets water escape from the thermostat housing, allowing the warm water to enter from the cylinders and begin to open the thermostats. If this pin hole becomes clogged, it will not allow this initial water circulation, water in the cylinder jackets gets hotter and it overheats.

My solution was to drill the pin hole out with a 1/8" drill bit. This solved my overheating issue. If you don't want to experiment on your original thermostat valve body, there are usually used parts available on Ebay. This part is common to many years and models.

I would not recommend running your engine without thermostats. Thermostats cause the back pressure needed ensure your water jackets completely fill. Good Luck

 

[durban]

Re: 1991 Johnson V 90 overheating at idle

the channel between the 2 blocks where the water comes up from the impeller has 2 point for the water to get in to the blocks wot happens at idle the water pressure is not so great the water then comes up the channel & enters the bottom hole in the channel & feeds the block from the bottom the water starts entering the block & the deflectors then guide the flow of water to the top of the block to exit out through another hole at the top end into the cylinder head cover & out to thermostat & poppet valves .

as the rpm increases so does the water pressure , when the water pressure increases the channel between the blocks fill up to the top the water then enters the top hole in the channel & fills the block & when the block has filled the water then exits out through another hole at the top into the cylinder outer cover & onto thermostats & poppet valves

the conclusion when the motor is at idle & low water pressure & entering the bottom hole in the channel to feed the block the deflectors for some reason then do not guide the water to the top of the block to keep it cool & to exit out the hole at the top of cylinder head into cylinder head cover & this is when it heats up , but shouldn't heat up when you throttle up because more water then enters the channel & feeds the block from the top this will only work if the motor is in the water & not on muffs

my plan B WORKS

 

[Fed]

Re: 1991 Johnson V 90 overheating at idle

That's not how it works durban, take a look at your genuine OMC manual and in the back you will find the water flow diagrams.

 

[emdsapmgr]

Re: 1991 Johnson V 90 overheating at idle

Dargel makes a great point about checking the valve body to make sure the bleed hole is open. I believe on your model, the valve body is the later design. It has a larger, single oval hole instead of the two pinholes. Anyway, check to make sure it is not plugged with any debris. The placement of the rubber diverters in the block is key to good cooling. The pic shows a correct placement. Salt, sand, weed buildup can start to restrict water flow between this rubber diverter and the opposite side of the block. Make sure there is no restriction for good cooling. If you have a concern about one head, pull the head cover off and check the cooling passages inside the head. If they are restricted, clean them out. You will find the rest of the block will be as clean or clogged as the head cooling passages are. If you head appears severely restricted, you may need to 1. remove both heads and check the rubber water diverter placement and clean any restrictions. 2. remove the other head cover and clean the head. 3. even open up the top of the block and have a look. (the large passage between the two sides of the block-under the water cooled rectifier/regulator.) A strong telltale only indicates the water pump is functioning. It does not indicate that any water is circulating through the block. When water starts to come out of the two exhaust relief holes at the top of the midsection, then the stats have opened and it's cooling. At idle the powerhead should heat up to between 143 and 155, with 155 being the max temp in a warm lake in the dead of summer.

 

[durban]

Re: 1991 Johnson V 90 overheating at idle

i could be wrong on the 1991 model the system i studied without a manual was for a 90hp 1982 & the blocks checking on a reference check does not list them the same as one rectifier sits in the channel & on another block it sits on top because when the rpm increases the water rises in the channel & goes into the hole at the top , if you don't believe me get a 1982 model take the rectifier of start the motor & increase the rpm & watch the water rise in the channel you will see where it flows into