1973 135hp Johnson overheating

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exyo

Recruit
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Feb 21, 2011
Messages
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I am hoping for some expert advice. I am not getting any water to the heads. Had a tune up at my mechanics then next time on start up the impeller went. Everything WAS working great. Replaced impeller, vernatherm, pulled heads and replaced diverters. Replaced hoses, gaskets etc. in thermostat (vernatherm) housing. Had lower unit off 3 times to make sure impeller is positioned properly. Diverters looked good but I replaced them anyway and no damage to pistons or heads. Any ideas?
 
oldcatamount

oldcatamount

Lieutenant Commander
Joined
Apr 4, 2010
Messages
1,740
Re: 1973 135hp Johnson overheating

When you replaced the impeller, were all of the old fins intact? I'm thinking you may have a piece of one of the fins lodged inside a water passageway. If you have to remove the lower unit again, rig up a garden hose to blow water upward thru the copper tubing, or you could use air pressure to do the same thing. Remove the t-stat housing cover and see if you're getting water to that point.
 
Faztbullet

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,938
Re: 1973 135hp Johnson overheating

If your not getting both the water and return tubes in impeller housing it can cause this....
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1973 135hp Johnson overheating

Temporarily disconnect the two rubber hoses from the each head to the stat housing cover. When you have the engine hooked up to the garden hose and intially start it, do you get any water out of these hoses? This is a similar test to the one recommended by oldcat.
 
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exyo

Recruit
Joined
Feb 21, 2011
Messages
2
Re: 1973 135hp Johnson overheating

Thanks for the great information. I suspect that some of the previous impeller rubber may be jammed in the water tubes. Due to knee surgery I have been down for the last few weeks but hope to explore the advice that has been presented. This is a great forum and again I thank you guys for the information and I'll keep you posted on my progress.
 
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