Johnson VRO 4, 90 HP. overheat problem one side of engine

[B1gM1ke]

After about 3 minutes running on the ears my warning buzzer sounded a steady buzz. Shut it off immediately and checked the temp of the cylinders. Right side was not even over 80 degrees yet, left side was at 194 degrees. Any ideas? I am wondering if there is a sepperate thermostat for each side and if so maybe that side thermostat is stuck. ???

 

[B1gM1ke]

ok so there is a thermostat for each side. before I go buying a new one can I get some feedback maybe on how to test my thermostat? Or perhaps any ideas on what else the issue may be that I should look into? Thank you

 

[bob johnson]

what model do you have???( don't say 90 hp!!) the overheat alarm usually goes off when you reach about 220 degrees I think.....but if you have A single thermostat, you probably have a crossflow v4....

I don't know too much about crossflows

let us know what model you have

bob

 

[SparkieBoat]

sounds like a thermostat to me. you can test it by putting it in a pot and heating up the water. I forget what temperature it should pop open at, maybe 150 or so.
here are a couple of helpful post on the subject.
http://forums.iboats.com/forum/engi...8spl-how-do-i-know-if-thermostats-are-opening
http://forums.iboats.com/forum/engi...ards/634378-1991-johnson-90-hp-v4-thermostats

 

[racerone]

Possibly the water deflectors are out of position and blocking water flow.

 

[Bosunsmate]

id start on your thermostats, put them both in the pot and compare.
Check your poppet valves arent deformed, thet a by the thermostats on lots of models

 

[B1gM1ke]

ok so heres what I have found. I do have 2 thermostats. One (the cool side I'm pretty sure) was open, the other (hot side I think was closed) this was hours after the engine had been shut off. I noticed the spring inside the thermostat itself on the open one was not set all the way down like normal. It was pushed like half way up inside the thermostat. the closed one looked normal. I dfid the test where you switch from cold water to boiling water. The one that was open stayed open no matter what, the closed one seemed to work correctly opening and closing when switched between hot and cold water. Here is my dilema. The "Hot" side thermostat seems to work correctly when tested. The "cold" side seems to be stuck open. Would having one side stuck open cause the other to stay closed and not open to let cold water into its cylinder bank? I plan on replacing both thermostats anyways but I just dont understand why I have a hot side if one is stuck open and the other works rite. Maybe one of you that understands these things better than I do can explain this?

 

[SparkieBoat]

did you check your poppet valves and deflectors as suggested?

 

[B1gM1ke]

what are poppet valves and deflectors?

 

[B1gM1ke]

oh the white plastic star like items next to the thermostats? yes they look fine, no deformity

 

[B1gM1ke]

not sure what grommets are

 

[Bosunsmate]

Good question, ive forgotten what those thermostat housings look like exactly.
Ive forgotten if they have channels to the thermostat specific for each bank or if they have some mixing in that rear section where the hoses join on.
The way they operate is that the little hole in the middle lets a little bit of water through which gradually lets the thermostats heat up as the engine does and it then starts opening the thermostats, so if yours was having a lot of cold water always flush it then it might not get hot enough to open up (if they were mixed channels) but then id expect the cold bank to get as hot as the hot bank as they would both be using the same outlet.

 

[Bosunsmate]

By the way i only put them into cool water and heat them up as im not sure if dropping straight into boiling water would stress out something.

Also have you relocated the telltale outlet on that engine to near the top as they can often get airbubbles in that starboard bank and overheat.
http://forums.iboats.com/forum/engi...aq/228380-johnson-evinrude-adding-a-tell-tale

 

[SparkieBoat]

the link that i posted above has a good picture showing you the placement of the deflectors. here it is. note the corrosion, this would need to be cleaned.

 

[B1gM1ke]

I wasnt concerned about damaging them with my hot cold water test because I already decided to replace both and yes they operate as you state above, the small hole was blocked also so the water was not getting thru it at least it looked that way. but the one t-stat was stuck wide open flushing both with cold water constantly . I am going to order both t-stats and new gaskets. but can someone please explain grommets to me. I see them in the picture of my motor but I cannot find them on my actual motor and can't see the pic well enough to know exactly what they look like

 

[B1gM1ke]

oh is the grommet a rubber ring thing almost like a thick gasket? If so I found them and they are ok

 

[Bosunsmate]

I bored that centre hole larger on my mates motor, i almost doubled its size to make sure it doesnt clog up, its the weakest part of that design. His motors never heated up since. Maybe thats had a part to play in your overheat. There must be some kind of specificity for each head otherwise why bother with two thermostats.
I suspect the grommets you are mentioning are what the poppets move in, Ive never had to replace those

 

[Bosunsmate]

If i remember rightly that rear housing has like a centre baffle in it.

 

[emdsapmgr]

The amount of deposits inside the cooling system can contribute significantly to any overheat. See the attached picture of how the cooling passages need to look. The rubber diverter just to the left is positioned correctly. The one to the right is out of position. Note how easily the cooling water will flow thru this block, as opposed to the one in post #14. In addition, there is either a pair of small holes, or one larger hole in the valve body of the thermostat housing. Those holes must be open in order for hot water to get to the back of the thermostats in order to heat them up to open. If the hole(s) are plugged or restricted, it can run hot. The valve body hole(s) vary depending on the age of the powerhead. Early models have two holes, later ones have the larger hole. At idle, all the cooling water goes thru the thermostats. If one is stuck shut, it's an overheat. As soon as the boat planes out, the pressure relief valves in the stat housing open, flooding the powerhead with tons of extra cooling water. The overheat horn comes on at 212 degrees. Shuts off at 175, which is still way too hot. The engine should idle at 143 to 155. That's normal. Much cooler when on plane.

 

[bob johnson]

what happened to listing the MODEL # of the motor???????????? they have different style motors... that have different style thermostats...of those motors doesn't have DEFLECTORS.... so the OP should list the model # of his motor!!!!!!!!!!!!!!!!!!!!!!