1991 Johnson 90 HP V4 Thermostats

[csprain]

I just mounted my 1991 johnson v4. Its a 90hp. I got it at a good price and after mounting it I have been having an overheating problem. I replaced the water pump. Previous owner put regular hose where pre-molded should be so I replaced those hoses. The head gaskets were bad so I am replacing them tomorrow. Really the only thing left that I can think of would be the thermostats. What are your opinions? Any tips on replacing them? Any pictures would be very helpful. I don't know a lot about the motor yet. I'm learning as I go. Thanks in advance.

 

[Fed]

Re: 1991 Johnson 90 HP V4 Thermostats

Water deflectors while you have the heads off especially if it's overheating at higher RPM.

 

[Bosunsmate]

Re: 1991 Johnson 90 HP V4 Thermostats

Thats the bubbleback model, ive never done one of them but i think removing the thermostat cover is difficult.
On the non bubbleback ive come across people drilling out bits of the backcover to get better access to them.
Check when your heads are off that the deflectors are still in place, i think theres two per side

 

[Bosunsmate]

Re: 1991 Johnson 90 HP V4 Thermostats

Good one Fred, i agree!
I also clip a circle and a half off the poppet spring so they open earlier, plus renew all gaskets and clean the poppet channels etc

 

[csprain]

Re: 1991 Johnson 90 HP V4 Thermostats

I alreadyremoved the heads because I my gaskets were suppose to be in yesterday afternoon. I went to pick them up and they weren't there. What do the deflectors look like? Where are they located?

 

[Bosunsmate]

Re: 1991 Johnson 90 HP V4 Thermostats

They a small cooling hoses shoved in to the water channels around the heads.
They squeeze down and block the channel as you shove them in

 

[Fed]

Re: 1991 Johnson 90 HP V4 Thermostats

I found a picture for you.
1 under each cylinder,4 in total.
They force the water up & over the top rather than taking a short cut under the cylinders.

 

[csprain]

Re: 1991 Johnson 90 HP V4 Thermostats

Is there anyways you can paste the image? Or email to it to my personal email, csprain@gmail.com? I cannot download it to view it.

 

[Fed]

Re: 1991 Johnson 90 HP V4 Thermostats

Just left click on it to view in full size.
I should have mentioned what happens is that corrosion & swelling causes the rubber tubes to intrude into the vertical passage blocking water flow around the cylinders.
They look like 3" bits of fuel line and slide into the little casting ridges.
Do a forum search for deflectors and you will find plenty of pictures.

 

[rscotth]

Re: 1991 Johnson 90 HP V4 Thermostats

Like FED said, if your overheating at higher rpm's like at plane it's likely to be deflectors and in my case impacted corrosion at the water inlet and discharge on both banks of the power head. The BRP part number for the deflectors is 0322411 if your looking to purchase these. You'll need 4, two for each head.

If your overheating at idle it could be a stuck thermostat (s) since higher rpm's overcome the poppet valves that allow water to leave the powerhead and allow cooling through the power head.

 

[csprain]

Re: 1991 Johnson 90 HP V4 Thermostats

I am out of town this weekend. I will look at those tomorrow and post a picture. I've never had an overheating problem at idle. Its always overheated after 10-15 minutes on the water. I really appreciate all the help thus far.

 

[emdsapmgr]

Re: 1991 Johnson 90 HP V4 Thermostats

The 90 engine that year is a flatback engine. Should not be much of a problem to replace the thermostats on that engine. When you have the valve body out of the thermostat housing, make sure the oval hole between the two stat holes is fully open. Also, check the nylon pressure relief valves to be sure they are not heat-deformed. You need those pressure relief valves to open fully when on plane for mid to high rpm cooling.