1973 Johnson V4 cylinder 1 overheating

[The boat man 12]

Had the engine running great last week. New impeller installed at the start of the season no more than 3 hrs on it. I thermally tested all the heads after the impeller installed and they all were all running at approximately 140 f. Then after I fixed a seal issue in the lower unit the other day and reinstalled LU, I find cylinder 1 is overheating badly at idol.( I don’t know at higher rpm too scared to take it out.) The temperature would rise steadily and I shut it down when it hit 200 f. There is definitely water going up and hot water coming down. Also, I flushed a small amount of hose water (with the LU off) up through the through coolant tubes and I could feel all the heads getting cold including the one that was overheating . Any ideas? Thanks.

 

[CaptnKingfisher]

Perhaps when you did the work on the bad seal, pieces of the seal got into the cooling system and is obstructing the flow of water around the head. Despite having owned a few of these V4s, I can't remember how the water gets to the exhaust, but if you can access it and backflush the system with a hose and or compressed air you can maybe free up any debris that could be lodged inside

 

[The boat man 12]

Perhaps when you did the work on the bad seal, pieces of the seal got into the cooling system and is obstructing the flow of water around the head. Despite having owned a few of these V4s, I can't remember how the water gets to the exhaust, but if you can access it and backflush the system with a hose and or compressed air you can maybe free up any debris that could be lodged inside

Ok thanks for the idea! Compressed air won’t hurt anything right?

 

[CaptnKingfisher]

Oof I thought I read this in my manual but I went back and double checked when you said that and dont see anything about blowing air into the cooling system. I probably read that for cleaning out fuel lines and filters. So I'd hafta say this came from my brain, not the manual and so I can't confirm that it's safe. Though I will say I've pressure tested I/O cooling systems (which requires pumping air into the system) and this is common practice to pump around 15 psi into a closed system. You have an open system so pressure won't be building up. I dont think it would hurt anything but can't promise. Proceed at your own risk. If you can backflush with a hose it'll probably do a better job anyway

 

[racerone]

Inspect ---water diverters.----Found in the engine block.----Cylinder head removal required.------These items guide water flowing through water jackets.

 

[The boat man 12]

Inspect ---water diverters.----Found in the engine block.----Cylinder head removal required.------These items guide water flowing through water jackets.

Oh thanks could this cause all the cool water to flow to the lower cylinder and not cool the to one?

 

[racerone]

Sorry I am too far away to look over your shoulder.----Perhaps it is just the cover on the cylinder head that needs to be removed for cleaning.

 

[tblshur]

I would try in lake or deep tub before going too far

 

[interalian]

 

[interalian]

 

[interalian]