1980 johnson 85 HP overheating

this motor starts and runs strong but it has overheated when under power. it will idle in the driveway all day but on the lake the alarm goes off after about 2 minutes. i have pulled the water jacket covers and cleaned and replaced gaskets. it has a strong stream when running so i did not think it was a water pump issue. i was wondering how much build up there could be inside the rest of the water system and how to clean it.

need help, been messing with this for about 6 months on and off, and do not want to miss another bass season!

Re: 1980 johnson 85 HP overheating

First thing to do is take the g/c off and do the water pump. If that doesn't do it pull the heads and check the water deflectors in the block. They may be swelled up causing poor water flow or you may have a blown head gasket.

Re: 1980 johnson 85 HP overheating

Follow boobie's comments. A strong telltale indicates the water pump is working, but the engine can still overheat if the water does not circulate through the block and exit into the exhaust housing. If it runs all day at idle, you may have some type of flow restriction. You said you removed the water jacket covers-I assume you mean the covers on each head. What did you find inside? Another thing to check: Pull the thermostat housing apart and make sure the nylon pressure relief valves are ok. These valves will open once the engine gets on plane and will flow significantly more water thru the block. These valves can deform if overheated so that they don't function as designed.

Re: 1980 johnson 85 HP overheating

emdsapmgr said:

Follow boobie's comments. A strong telltale indicates the water pump is working, but the engine can still overheat if the water does not circulate through the block and exit into the exhaust housing. If it runs all day at idle, you may have some type of flow restriction. You said you removed the water jacket covers-I assume you mean the covers on each head. What did you find inside? Another thing to check: Pull the thermostat housing apart and make sure the nylon pressure relief valves are ok. These valves will open once the engine gets on plane and will flow significantly more water thru the block. These valves can deform if overheated so that they don't function as designed.

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there was a lot of white deposit that i was able to clean off. it looked like calcium you find in your kitchen plumbing. i could tell by the pain on the bolts that these covers had not been removed before. so you are thinking that even if there is a good telltale that the water pump may need to be replaced? can you direct me to a blow up of the engine to identify the other items that you have refered to?

thanks for your comments.

Re: 1980 johnson 85 HP overheating

If you have a lot of calcium buildup inside the head, that can restrict water flow-esp at higher rpm's. I'd make sure you get them cleaned out, then reinstall. If the heads are calcified, it is possible the cooling passages around the cylinders are also. You may want to just pull the heads and have a look. Esp, look for flow restrictions by the rubber water deflectors, as boobie mentioned. Often they can even get pushed out of place, causing flow restrictions. If you see a lot of restrictions when you get the heads off, you may need to pull the water passage cover off the top of the engine and have a look inside there also. (have to pull the flywheel.) Bombardier makes nice parts diagrams which you can access on the web: epc.brp.com. They are good illustrations for service work and handy if you need specific part numbers.

Re: 1980 johnson 85 HP overheating

Has this mtr been run in salt water??

Re: 1980 johnson 85 HP overheating

If there's calcification in the water jacket covers, there's likely buildup in the heads themselves. You should pull the heads and clean them out and also put in new water diverters. Bet that fixes it.

Re: 1980 johnson 85 HP overheating

to all of you who have commented, thank you. i am happy to report that it was the water pump impeller "housing" (a plastic piece). so although the impeller was pulling the water up and sending it out the tale tell tube, it would not provide enough pressure to push it though the block for cooling.

easy fix...

Re: 1980 johnson 85 HP overheating

Now that you have that solved, being it's been overheated numerous times, it's probably a good idea to do a compression test to make sure you didn't ruin a head gasket.

It's also not a bad idea to check the thermostat and make sure it wasn't cooked, inside the T-stat housing you will also have 2 pressure relief valves. If they get good an hot then they can melt and become non functional.

Re: 1980 johnson 85 HP overheating

Good find.

I am still keen to learn what the actual issue was.

It is stated that it was the water pump impeller "housing" (a plastic piece).

So, what was it about this plastic piece that caused the problem?

CH1968

Re: 1980 johnson 85 HP overheating

Plastic housings can wear over time, especially in motors that are run in high sediment/sandy areas.