one cylinder head hotter than other on 85hp johnson

[iRich]

Hi all, I started my motor today, (1975 85hp johnson), and after running it a few minutes on the muffs I noticed that the right cylinder bank,(if looking at motor from the back), gets considerably hotter than the other side. I can still hold my hand on it quite awhile but the other side barely seems to get warm. Is this normal? Thanks,<br />Rich

 

[Joe Reeves]

Re: one cylinder head hotter than other on 85hp johnson

iRich.... The 1975 85hp only has one thermostat and since you have one bank running hotter than the other, and that other barely gets warm, I would assume the following.<br /><br />The thermostat is either stuck open or missing which would account for the cold bank.<br /><br />And the water deflectors (see service or parts manual) on the hot bank are swelled outward resulting in a water restriction. This would account for this bank running hot.<br /><br />Cure.... Remove both heads and install new water deflectors on both banks, and install a new thermostat.<br /><br />Installing the thermostat in that model is a first class pain! You might find yourself drilling a couple holes in the lower pan in order to get at those bolts.<br /><br />The water deflectors can be drug out with a hooked pointed scribe. Clean out the surfaces where the deflectors go with a small file or whatever otherwise you'll never get the new ones in. To ease the installation of the new deflectors, spray the metal surface and the deflectors themselves with WD40 which will act as a lubricant. Sometimes it helps to insert the hook end of a pointed scribe into the deflector near the inner end to help push it where it belongs (all the way in).

 

[iRich]

Re: one cylinder head hotter than other on 85hp johnson

Hi Joe, Thanks for the quick response and great advice. I actually have a thermostat and was going to change it today but couldn't get the housing off because the motor housing is in the way. The only thing I could see to do would be to loosen the motor mount nuts and raise it a little to get the clearance. Does this sound right? I know I need a manual and I'm going tomorrow to buy one. As far as the deflectors you mentioned, are they easily replaced once the heads are off? Any special tools or knowledge required? Would the thermostat cause one bank to get hotter than the other? If so how? thanks again,<br /><br />Rich

 

[Joe Reeves]

Re: one cylinder head hotter than other on 85hp johnson

iRich..... I revised my original post. Reread it.

 

[iRich]

Re: one cylinder head hotter than other on 85hp johnson

Hey Joe..good idea about drilling holes to get the bolts out. I will do that. I guess to change the deflectors I'll need new a head gasket and the deflectors...anything else I might need? Thanks for the advice,<br /><br />Rich

 

[iRich]

Re: one cylinder head hotter than other on 85hp johnson

Joe Reeves, You were right about the water deflectors, they were swelled up and blocking the flow of water. I broke three head bolts getting it off. I got one out and can drill the other two, just wondering if it is better to use heli coils or tapping a new hole? It seems like the heli coils would be easier. Also, are there water deflectors in the head itself under the water jacket cover? I didn't want to buy a gasket for it if there isn't and the book isn't too clear on it. Thanks for the help everybody,<br /><br />Rich

 

[ledgefinder]

Re: one cylinder head hotter than other on 85hp johnson

A propane torch will help a lot in getting those studs out. The studs are steel & the blocks aluminum, so heating things up & cooling them down a few times creates a lot of relative motion, breaking the stiction.