1961 18hp johnson overheating

[Reidstra]

New impeller, thermostat. Started water pump working as water comes out on high idle but very little on low idle which i believe is normal for this year. Ran 2 minutes temp gun shows 170f upper 200f lower with thermostat removed. Compression 90psi both cylinders. I'm thinking my next move is head gasket. I need advice before i go any farther. Please

 

[Reidstra]

New impeller, thermostat. Started water pump working as water comes out on high idle but very little on low idle which i believe is normal for this year. Ran 2 minutes temp gun shows 170f upper 200f lower with thermostat removed. Compression 90psi both cylinders. I'm thinking my next move is head gasket. I need advice before i go any farther. Please

Model rd-15

 

[oldboat1]

Sounds like the pin may not be locked into the impeller. You should see 120 to 140F --160 or over is overheating. Test in a barrel (plastic garbage can) with water 6-8 inches above the water pump -- half way up the shaft is a good rule of thumb to be safe.

 

[Reidstra]

Sounds like the pin may not be locked into the impeller. You should see 120 to 140F --160 or over is overheating. Test in a barrel (plastic garbage can) with water 6-8 inches above the water pump -- half way up the shaft is a good rule of thumb to be safe.

Yes had it in lots water. Pin must be in as water discharging when i increase idle.

 

[Sea Rider]

That's a 61 year oldie, fresh or salt water use, bought it new or second, third hand ?

Happy Boating​

 

[Reidstra]

That's a 61 year oldie, fresh or salt water use, bought it new or second, third hand ?

Happy Boating​

Its my friends. 2nd owner. Fresh water. Runs good just runs to hot

 

[racerone]

Motor should pump lots of water at low idle !!----Was the copper tube installed into the exhaust housing first ?------Possibly one of the water tube grommets is messed up.-----Factory water pump impeller or something else from that ----A ---company ?

 

[Reidstra]

Motor should pump lots of water at low idle !!----Was the copper tube installed into the exhaust housing first ?------Possibly one of the water tube grommets is messed up.-----Factory water pump impeller or something else from that ----A ---company ?

I just opened and checked water pump and its all good. Wondering if tube or water jacket may have blockage? How would i check this?

 

[bwkre]

Could be a bad thermostat, easy to remove and test.
here is a video of my 61 18hp running in a bucket for comparison. Not a lot of water from the exhaust relief but it was running about 105 F at the time.
easier to see full screen

+

 

[oldboat1]

Maybe you are overstating the running temp. If testing with an infrared tester, try another one. If it's too hot to touch, it's running too hot -- and 170-200F would burn your hand. Having said that, temp is measured at the top of the head, not the face around the plugs (which is hotter).

 

[oldboat1]

If it's really running as hot as you say, remove the lower unit, and flush upwards through the copper water tube. Water should gush down. If continued issues, remove the head cover and clean out the water passages around the cylinders. You can also flush downward with the t.stat removed.

 

[Reidstra]

Could be a bad thermostat, easy to remove and test.
here is a video of my 61 18hp running in a bucket for comparison. Not a lot of water from the exhaust relief but it was running about 105 F at the time.
easier to see full screen

+

I bought new thermostat but running it without thermostat right now and still running too hot.

 

[racerone]

There is not enough water in your test bucket !!----Add 6" (15 cm )of water and test run.----Motor does not sound right to me.

 

[Crosbyman]

if you have a fiber optic camera/cable you could try to go up the water tube for a peek in case something obvious shows up. Outboard colonoscopy


beyond that see post #11 from oldboat1

 

[Reidstra]

Thats not my motor thats someone thst replied to my issue

 

[racerone]

Oh well.----It should be easy to diagnose overheating on a simple 18 HP motor.