Engine Running Hot

[ruddy mudder]

1983 90 hp Johnson running hot @ 176 degrees at idle after new thermostats, gaskets, poppet valves and springs. Hoses disconnected from the heads shows more than enough water flow. Thermostats removed, cylinder head temps @ 100 degrees. Exhaust cover remains consistantly at 85 degrees with or without thermostats. No blockages appear to be in powerhead. Rev the engine and poppet valves open up and won't reseat when resuming idle RPM, thermostats were reinstalled allowing the engine to run around 140 degrees keeping it from running hot I would presume. Thermostats were tested in boiling water and opened up at approximately 140 degrees using a temperature gun. Need to figure out why the poppets won't close at idle speed, but when closed with thermostats installed, engine still will run hot. Any suggestions would be greatly appreciated. -- Ron

 

[Ronniewhite]

1983 90 hp Johnson running hot @ 176 degrees at idle after new thermostats, gaskets, poppet valves and springs. Hoses disconnected from the heads shows more than enough water flow. Thermostats removed, cylinder head temps @ 100 degrees. Exhaust cover remains consistantly at 85 degrees with or without thermostats. No blockages appear to be in powerhead. Rev the engine and poppet valves open up and won't reseat when resuming idle RPM, thermostats were reinstalled allowing the engine to run around 140 degrees keeping it from running hot I would presume. Thermostats were tested in boiling water and opened up at approximately 140 degrees using a temperature gun. Need to figure out why the poppets won't close at idle speed, but when closed with thermostats installed, engine still will run hot. Any suggestions would be greatly appreciated. -- Ron

New impeller maybe

 

[saltchuckmatt]

What brand of thermostat?

 

[Scott Danforth]

first step is always the impeller.

 

[racerone]

Running on a hose in the driveway ?

 

[ruddy mudder]

New water pump kit, Pro Marine thermo kit, running on flushers. Plenty of water gushing from heads without hoses attached to them. Will barrel run in a couple of days, but water supply shouldn't be the issue, more than enough coming from the heads. T-stats open up at 140 degrees in pan of hot water, accurate temp gun used.

 

[kbait]

Barrel test with water deep enough to submerge waterpump. Muffs are not a realistic waterpump/cooling system function test. Hopefully it cools normally.
If it still overheats, pull heads and check water passage deflectors #12.. supposedly 4 per engine/one per cylinder.

 

[F_R]

I keep saying it---you can't test a water pump on muffs. Get it off those muffs and onto the lake.

 

[oldboat1]

^^like he says. There is a middle ground for idle testing, though. Get a 32 gal plastic trash can, and tuck it up under the shaft. Fill full or nearly full -- water well up on the shaft. Run at idle while monitoring.

 

[ruddy mudder]

Are the poppet valves supposed to open when the engine runs just above idle? Thought they opened when a higher RPM produces greater water pressure from the pump? Never known for them to open at a fast idle.

 

[ruddy mudder]

Barrel test with water deep enough to submerge waterpump. Muffs are not a realistic waterpump/cooling system function test. Hopefully it cools normally.
If it still overheats, pull heads and check water passage deflectors #12.. supposedly 4 per engine/one per cylinder.
View attachment 375884

Deflectors are good, replaced them when the heads were off, looked like the originals.

 

[racerone]

Hint.----You say pressure opens the poppit valves.-----So what pressure do you have on your water supply hose???-----Test it in the lake !

 

[ruddy mudder]

Engine was run in a barrel and the poppets still opened. Engine running around 140 degrees regardless, guess that will be the norm for this one, at least not overheating. Thanks for all the suggestions from everyone.