Overheating problem Johnson 35HP 1982

[copus]

Engine runs great now, but after running at 3500 rpm for about 10 minutes it slowly heats up and dies. So far I have replaced the impeller,new powerhead base gasket, new head gasket. I dropped the lower unit and checked the water inlet tube for a restriction. I removed the thermostat. The block and cylinder head run very hot, but the exhaust water jacket runs cool. Exhaust and telltale run cool.Is there some way I can check inside the block for a restriction? What about filling the block with some type of acid or cleaning solution. As a last resort I'm thinking of piping the telltale (where it exits the exhaust water jacket)to the top of the cylinder head water jacket and exiting at the bottom. Any thoughts?<br />Thanks,<br />Ron

 

[norman158]

Re: Overheating problem Johnson 35HP 1982

try putting the tstat back in its there for a reason it also acts a a restrictor to slow down the water flow so asorbes the heat better

 

[oldboat1]

Re: Overheating problem Johnson 35HP 1982

I believe the water exits the tell-tale before it circulates through the head -- sounds to me like you might have a restriction in the water passage somewhere. I think I would remove the lower unit again and try to force water up through the tube. This flushing might be enough to clear a blockage in the head. The next step would be to remove the head and clean out the passages -- may also be necessary to remove the exhaust port cover and do the same thing.

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Hi again Copus<br /><br />Are you sure you got the correct headgasket ?<br /><br />the buttom of the headgaskets changed design in 1981 i think and an older gasket would block the water outlet in the buttom of the cylinderhead to the leg. As you have a strong steady stream at tel-tale you will have water pressure at thermostat too. Did you check in a glass with hot water that thermostat functions ?

 

[copus]

Re: Overheating problem Johnson 35HP 1982

norman158.. I had the thermostat in when it heated up the first time and then took it out and still no change.<br /><br />Oldboat...I'm thinking like you that there is a restriction in the block somewhere. The problem is where, and getting it out. I'm going to remove all water jackets and the cylinder head tomorrow and the lower leg and try to force some water under pressure thru the thermostat housing.<br /><br />GDane.. Hi again. Well, the motor is running great now except for the overheating problem. I checked the old head gasket, which is the same as the one in there now, and it does have the slots at the bottom. I have a parts manual for this engine and the headgasket is genuine OMC.Will tear it apart tomorrow and see if I can find any blockage. BTW, the guy I bought it from had the same problem and he could'nt solve it.<br />Will keep y'all informed.

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Copus - before you tear it apart - the water goes up through the tube from the waterpump, through the exhaust cover ( where corrosion round the little rubber bushing sometimes can squeese the bushing and cause restriction ) through the exhaust jacket, and from there directly to the thermostat housing. From the thermostat back, it enters as well block as cylinderhead jacket.<br />Water can be restricted in two ways: If it cant enter block/cylinder head og if it cant leave. As you have tell tale stream, you have water pressure most of the way. Unscrew the water jacket on the cylinderhead and see if the water reaches the thermostat. If it doesnt, you can clean the hole to the exhaust jacket from there.<br /><br />If it does, and thermostat is working ( test as I suggested ) Water probably cant leave jacket. <br /><br />Both gaskets have slot at buttom, the old type is straight at buttom, the new from 81 and up has a little pocket out with the slot. You have to compare the gasket to the head to be sure, especially if someone else have been working on this. The block needs to have 3 small rubber restrictors, looking like small pieces of rubber hose. They force the water to circulate round in block/through the small holes in gasket and back again to make a good cooling. Is the motor put together from more than one motor - sometimes different parts can be used, from new/older model and CAN be, but you have to make sure they fit together, especially block/head. Slower water circulation wount make a better cooling, if water passes, it will cool. removing thermostat that functions will only make your motor running cool, loosing economi and performance. Keep me posted.

 

[copus]

Re: Overheating problem Johnson 35HP 1982

G DANE... I removed the cylinder head and the water jacket. Everything in there is clean.My headgasket has 3 slots on the bottom and matches the head and water jacket.I have 2 restrictors, one at the top and one at the bottom. My parts manual says the electric start has 3. I don't have electric start. The upper restrictor dosn't reach all the way to the bottom of the water jacket cavity,there's about a 1/2" space where the water can get through.Bottom is OK. Would that make a differance?<br />Tomorrow I'm going to drop the lower part of the leg and attach a water hose to the inlet pipe and see how much water comes in around the cylinders.As far as the thermostat, once I get the water flowing and I know its running cool, I'll install one. As far as I can tell this motor has all original parts. Any more ideas are welcomed.

 

[copus]

Re: Overheating problem Johnson 35HP 1982

I dropped the lower leg and attached a water hose to the inlet pipe. I have water coming in at the exhaust housing, no restrictions there.From there it goes to the lower cylinder and fills around them. Water comes out of the thermostat housing and with the jacket on goes out the lower leg. I think the water around the cylinders does not move enough with the impeller. I'm going to run the motor with the hose connected to the input tube and see if it runs cool. If it does I would suspect the water pump impeller,(although it's new), or the deflectors or...??

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Copus<br /><br />Concerning the restrictors, everything sounds fine. The one should be a little shorter. However both electric start and manual have the same number, if your manual says something else, i think its an error, the motors are identical, besides of starter bracket, charging devise, and wiring. But one missing rubber restrictor wouldnt make that difference. If you have water entering and leaving, if will cool it. When you had the head off, did you compare it to the block, i think they changesd in 1979, an old head probably wount let water pass in the right amount.

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Copus<br /><br />You can check the gasket/head design, by comparing 18-3803 gasket which should fit your motor to old type 18-2954 - old type, fits old block and head on thes web page, page 336/337:<br /> http://www.theshadconnection.com/cgi-bin/page.cgi

 

[copus]

Re: Overheating problem Johnson 35HP 1982

G DANE... Thanks for that info. I compared my head gasket to the newer one and it is exactly the same. The cylinder head and jacket all match up perfectly.As for the deflectors, my info comes from a genuine OMC parts catalog printed in 1982 that I got off Ebay. It shows the electric start deflector with a differant part number, but as you said, it probably wouldn't make that much difference.<br />The impeller I had installed is, I think a Sierra. Do you think an OMC would make a differance?

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Impeller make shouldnt matter, especially as you have water in exhaust jacket. Is the hole from thermostat housing into exhaust jacket blocked, i. exa by old impeller fragment ? When you put a hose on the water tube, do you have water at thermostat housing ? Lots ?

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Funny enough, the two of mine are both manual start and both have 3 restrictors - figure that !<br /><br />But I am sure it makes only minor differences, it aint your problem

 

[copus]

Re: Overheating problem Johnson 35HP 1982

With the cylinder head water jacket off, and the hose running into the inlet tube , water will come out at the bottom of the cylinder head unless you block it with a plate. Then it comes out at the thermostat hole. I've checked every passage and they are all clear. I'm going to go and talk to the guy I bought it from and find out when and how this overheating started and if it ever ran cool for him.

 

[copus]

Re: Overheating problem Johnson 35HP 1982

BTW, I still have one new deflector left, so I can always put it in the third slot.

 

[copus]

Re: Overheating problem Johnson 35HP 1982

Spoke with the guy that sold me the motor. He says that the motor ran cool for him until one day when it overheated and just stopped. He checked the impeller and it was shot. it was still in one piece so he replaced it and thats when the trouble started. Then he sold it to me. I'm waiting for my new gasket kit to come in and I will try running the engine with the hose connected to the inlet tube. Will keep you posted. Thanks, Ron

 

[G DANE]

Re: Overheating problem Johnson 35HP 1982

Copus - This is a long shot - is the bottum plate under the water pump in place ? It sound like the pump doesnt work as it should.

 

[copus]

Re: Overheating problem Johnson 35HP 1982

G DANE... I had a similar thought that the pump might not be picking up enough water through the bottom of the cavity. When I change the impeller I will check that out. Thanks.

 

[oldboat1]

Re: Overheating problem Johnson 35HP 1982

The wear plate under the impeller should be perfectly smooth, and the housing should seat perfectly. Use some gasket sealer under the wear plate edges and the housing edges to make sure there is no air being drawn in. Additionally, rub a small amount of grease on the wearplate under the impeller.<br /><br />Did you try running the motor without the thermostat installed (i.e., Are you sure the thermostat is working/opening?)

 

[copus]

Re: Overheating problem Johnson 35HP 1982

oldboat 1... The first time it overheated the thermostat was in, so I removed it and it still overheated.