79 Johnson 140 V4 Thermostat Replacement

[dosgatos]

Would anybody happen to know the replacement procedure for changing out the thermostat(s) on a 1979 Johnson 140? There is a huge gray area when it comes to the cooling system in the Seloc manual other than the water pump. Your help would be much appreciated!

Thanks!

 

[Vic.S]

Re: 79 Johnson 140 V4 Thermostat Replacement

There is a huge gray area in the Seloc manual

That's the trouble with non OEM manuals.

Enlarge THIS DIAGRAM fully and you'll see all the bits and pieces at the top.

The PARTS LIST identifies them.

Note carefully how it is all assembled as you strip it down as there is some discrepancy between what is in the diagram, what is in the manual and what is in the instruction sheet with the new parts it would seem from past discussions on here

 

[dosgatos]

Re: 79 Johnson 140 V4 Thermostat Replacement

Thank you very much! That helps a great deal. I am under the impression by the illustration that there is only one thermostat housed. I have a bit of a rough idle and the heads are cool after 10 minutes running with an occasional "cough" or hesitation in the idle. Judging by what people have posted on iboats, i would think it's the t-stat. just finished rebuilding the carbs, checked the manifold and reed box. Reeds are in mint condition.

 

[out 2 launch]

Re: 79 Johnson 140 V4 Thermostat Replacement

Actually there are two thermostats, one for each bank of cylinders.

 

[Vic.S]

Re: 79 Johnson 140 V4 Thermostat Replacement

Actually there are two thermostats, one for each bank of cylinders.

And two pressure relief valves.

 

[emdsapmgr]

Re: 79 Johnson 140 V4 Thermostat Replacement

Getting into the thermostat housing on this engine is a bear. You might want to borrow/rent a laser temp gun and see if it is running cool or not. At idle you should see 145-155 on each head when fully warmed up. A lean sneeze can also be related to a carb issue rather than a cool-running issue. You may have a restriction in one of the carb idle ciruits, causing an occasional sneeze and the rough idling you mentioned.

 

[dosgatos]

Re: 79 Johnson 140 V4 Thermostat Replacement

Thanks for all the input guys. I have a couple of comments:

Okay, so there is 2 thermostats in there. I will purchase 2. My guess is that they haven't been changed since the 80's or 90's as this is an old engine attached to an old boat. The plus side is that the boat floats and the engine runs! You mentioned pressure relief valves. Huh...what is this, an old boiler? Correct me if I am wrong, but isn't an engine's thermostat a pressure relief valve in effect. I betcha there's no thermostats in there anyways.

I am guessing that if I can hold my hand on the head and it feels cool to the touch, that it is running cool. I performed a complete rebuild on the carbs and there is no indication of malfunction there. That's after a pre and post inspection of them both.

I wish there was a manual to read, refer to, and guide thru the replacement.

Any suggestions?

 

[emdsapmgr]

Re: 79 Johnson 140 V4 Thermostat Replacement

When you tore the carbs down, did you spray an aerosol carb cleaner through all the passages and examine the spray patterns from one carb's passage flow rate to the same passage other on the other carb you cleaned? Dried fuel in idle (passageways) circuits is not readily visible. You can get an original service manual hard copy from the original publisher-Ken Cook Co., in Milwaukee. Either give them a call or contact them through their website. The pressure relief valves are situated next to the thermostats in the thermostat housing. When on plane, water pressure opens them to permit massive water flow through the block for additional cooling. You'll want to check them for proper functioning when you have the housing apart. These valves are nylon and you will want to make sure they are not heat-deformed from a prior overheat during the life of the engine.

 

[rodbolt]

Re: 79 Johnson 140 V4 Thermostat Replacement

what your looking for simply doesnt exist.
T stat and pressure control system is all in the same housing and its simply difficult to access yet nessasary for correct engine operation.
if its a freshwater motor it wont be bad just a pain.
}if its a salt water motor and it hasnt been done you may see snapped bolts.
easiest way is to remove both head water hosses,remove the lower cowl trim,remove the 3 housing bolts and remove and clean the housings, careful as the t stat holder is plastic.
if salt corrosion has locked the bolts use a sharp chisel and a hammer and split the housings.
if the fasteners are not corroded it takes me about 1.5 hours to change them on that motor.
if that engine is run without t stats or they are stuck open idle quality suffers.

 

[dosgatos]

Re: 79 Johnson 140 V4 Thermostat Replacement

Thanks for all the help! You guys on iboats are the best! I've also discovered that the 2 ignition coils on the port side are the wrong ones. They are p/n 582508 and this engine requires p/n 584561. I am wondering that after the engine is running for a short period of time that the coils are overheating and breaking down which could cause a hesitation. We had an antique car my father owned with the same issue. It was just plain old difficult to find a working coil for a 1924 Dodge Bros. prior to the internet revolution. In any event, I would still think it is prudent to inspect those t-stats and pressure relief valves, no? Any telltales of proper operation without visual inspection? It's definitely cooler than hotter, that's for sure.

Thanks!

 

[ezeke]

Re: 79 Johnson 140 V4 Thermostat Replacement

It would be a very good idea to service the thermostats.

iboats sells a kit with everything normally required: http://www.iboats.com/mall/partfind...gd_poid=111072&gd_row=47&**********=910954838

 

[dosgatos]

Re: 79 Johnson 140 V4 Thermostat Replacement

I think you're right! So much, I ended up removing the housing to find that there are no thermostats or pressure relief valves. Need those valves. Are they available on iboats? Also snapped one of the bolts. It was seriously rusted out so I guess I will have to drill and back it out. Worth investigating though. I hope I can figure which way ther t-stats and valves go in. I have the Johnson parts catalog illustration to go by I guess.

 

[emdsapmgr]

Re: 79 Johnson 140 V4 Thermostat Replacement

You should be ok if you follow the parts catalog illustration. The service manual uses the same diagram.

 

[ezeke]

Re: 79 Johnson 140 V4 Thermostat Replacement

iboats sells the poppet relief valve; part # 18-3564: http://www.iboats.com/mall/partfind...gd_poid=111025&gd_row=14&**********=044882859

This diagram link from Teleflex/Sierra will help:
http://ww2.sierramarine.com/catalog_pdf_8025/8025-195.pdf