new engine overheats

Scott Danforth

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generally, speaking an overheat is a lack of water flow.

either flow in or flow out

are these new manifolds? or did you reuse the old manifolds
did you back-flush the power steering cooler and lines from the thermostat housing back to the transom?
 

Scott06

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I went ahead and opened up the T-stat housing and found the stat was the one I put in when I re powered in 16. it never was taken out or changed by anyone else after all.. I put a NEW stat in anyway it and I took it to a pond to test rather than wondering if the hose was feeding it enough. it stayed cool for 15 min easy,, it took some time for the t stat to open and it stayed in parameters for a while idling around near the ramp so I motored out in the pond,, still fine I brought it up on plane ,, it stayed right about 165-170 for a bit,, 3/4 - a mile I'd say,,, then started creeping up again. at about 190 I put it in neutral at a high idle and it stopped rising but didn't drop much so I shut it off and went and opened up the motor drain ftfoi and emptied the motor. fired it up and it cooled instantly, another loop around the pond and sure nuf it started getting hot again.
so off comes the outdrive,, maybe the o ring at the gimbal is pinched,, maybe the ring between the two half's is punched/leaking,,,
Before taking it apart while its on the lake and temp is getting up in the 190 range- take the hose off the thermostat housing where water comes up from the drive. There is a merc procedure with more detail but basically should get 3-4 qts in 15 seconds. Would also look for bubbles indicating air or more likely exhaust gas is being pulled in.

this would give you a good diving point of where to look. Too little flow work backwards from there. enough supply flow work forwards.

Based on what you are saying - on plane I wonder if you are either pulling exhaust gas in under base of water pump, have pinched flow maybe in transom hose or plugged PS cooler, or are bypassing water at thermostat housing if you have the T with check balls /warm manifold system
 

Scott Danforth

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at 1000 RPM, the merc Alpha raw water pump should fill up a 5-gallon bucket in 16-20 seconds.

it should also shoot about 6-8" up from the end of the hose if held vertically off there thermostat.

I second Scott's theory that on plane is the raw water pump housing is leaking a bit and sucking in exhaust from inside the leg.
 

Lpgc

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Is the temp gauge working properly?

I seem to have been having the opposite problem (over-cooling) but I am adding a 2nd temp sensor to my carb'd SBF intake manifold to feed a cheap Runleader combined tacho / temp gauge unit to verify the dash temp gauge is reading correctly. I think the dash gauge is working properly, after the engine runs too cool I pull the stat to clean it, usually find some debris holding it open, put it back in and the engine runs at normal temp again for a while... But I want to confirm the dash gauge is working properly and having the self powered completely separate digital temp reading will do that. I orginally bought the Runleader to confirm the dash tacho was working properly but it comes supplied with a temp sensor, might as well fit it especially given my problem. I just need to find somewhere on the inlet manifold to fit the additional temp sender to but it has M6 metric threads...
 
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svb165

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generally, speaking an overheat is a lack of water flow.

either flow in or flow out

are these new manifolds? or did you reuse the old manifolds
did you back-flush the power steering cooler and lines from the thermostat housing back to the transom?
they are new manifolds. I will be flushing EVERYTHING again today. backward and forward.. it was acting Better" after putting in the new stat but it did still got hot so ?
 

svb165

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Before taking it apart while its on the lake and temp is getting up in the 190 range- take the hose off the thermostat housing where water comes up from the drive. There is a merc procedure with more detail but basically should get 3-4 qts in 15 seconds. Would also look for bubbles indicating air or more likely exhaust gas is being pulled in.

this would give you a good diving point of where to look. Too little flow work backwards from there. enough supply flow work forwards.

Based on what you are saying - on plane I wonder if you are either pulling exhaust gas in under base of water pump, have pinched flow maybe in transom hose or plugged PS cooler, or are bypassing water at thermostat housing if you have the T with check balls /warm manifold system
it over heated on the hose before replacing the t stat. and in a poor test the old stat dID open in a pan on the stove. although i didn't have a working thermometer and it didn't open til the water was almost at a boil so that didn't rreally tell me squat. another day flushing and testing and I will see. if no progress then I will split the drive and re seal the base plate and pump.
 

svb165

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Is the temp gauge working properly?

I seem to have been having the opposite problem (over-cooling) but I am adding a 2nd temp sensor to my carb'd SBF intake manifold to feed a cheap Runleader combined tacho / temp gauge unit to verify the dash temp gauge is reading correctly. I think the dash gauge is working properly, after the engine runs too cool I pull the stat to clean it, usually find some debris holding it open, put it back in and the engine runs at normal temp again for a while... But I want to confirm the dash gauge is working properly and having the self powered completely separate digital temp reading will do that. I orginally bought the Runleader to confirm the dash tacho was working properly but it comes supplied with a temp sensor, might as well fit it especially given my problem. I just need to find somewhere on the inlet manifold to fit the additional temp sender to but it has M6 metric threads...
It seems to be.
 

Scott Danforth

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how hot did it get on the hose? could have burned the flappers and rubber exhaust hoses.
 

svb165

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how hot did it get on the hose? could have burned the flappers and rubber exhaust hoses.
sorry I read that wrong. it got over heat hot on the hose before changing the stat. and ithen t ran cool for at least 15 min at idle putting around near the ramp. even under way slowly. it didn't rise til after a few minutes at about 3200 rpm then once hot it didn't want to cool.
 
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Grub54891

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What temperature thermostat is in there? Around here 140* is the common standard for freshwater cooled. Closed system is hotter stat.
 

svb165

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it calls for a 160* according to the marine store and what info I have found. that's what I pulled out AND put back in.
 

Scott06

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it over heated on the hose before replacing the t stat. and in a poor test the old stat dID open in a pan on the stove. although i didn't have a working thermometer and it didn't open til the water was almost at a boil so that didn't rreally tell me squat. another day flushing and testing and I will see. if no progress then I will split the drive and re seal the base plate and pump.
Do some testing first - if you have the volume at the thermostat and there are no bubbles then there is no reason to split the drive again.

You can also put a short section of clear hose in (home depot) to see if you are getting bubbles
 

Scott Danforth

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could your gauge be reading off? verify the temp with an IR thermometer. aim at the intake manifold cross-over just under the thermostat housing.
 

Lpgc

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could your gauge be reading off?
I asked the same in post #25, my dash gauge says the engine runs too cool but I don't fully trust the gauge so will be installing a completely independent 2nd gauge. Don't want to take the thread off track but I'm wondering how/where to fit the sender for the 2nd gauge, I already have a sender and digital display to suit but the sender uses short M6 threads. Wonder if I should drill and tap the inlet manifold and if so where on the manifold (carb'd SBF). The overheat / low oil pressure buzzer doesn't work anyway, maybe I should remove the overheat sender and make an adapter so the new sender can fit where that was fitted.
 

svb165

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I believe the gauge is correct. after start up and wam up it rises to just shy of half way between 160 -180 and sits there till it creeps. every time from a cold start it sit right there. ? today it ran perfect n the hose again, right there. then in the water it did the same, started out ok then a little ways into being on plane and the temp rises. I flushed about everything and I'm sure there are no obstructions anywhere. now running the boat on the muffs I pulled the water hose off the PS cooler where it comes in the boat,, and got a ton of air mixed with the water,, it was flowing ok but lots of air with it. that could be the hose muffs I spoze? I will actually measure it when I can.
the motor is definitely getting hot, but the risers and even the manifolds stay cooler. I don't get it, i will have an IR thermometer tomorrow.
 

Scott06

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I believe the gauge is correct. after start up and wam up it rises to just shy of half way between 160 -180 and sits there till it creeps. every time from a cold start it sit right there. ? today it ran perfect n the hose again, right there. then in the water it did the same, started out ok then a little ways into being on plane and the temp rises. I flushed about everything and I'm sure there are no obstructions anywhere. now running the boat on the muffs I pulled the water hose off the PS cooler where it comes in the boat,, and got a ton of air mixed with the water,, it was flowing ok but lots of air with it. that could be the hose muffs I spoze? I will actually measure it when I can.
the motor is definitely getting hot, but the risers and even the manifolds stay cooler. I don't get it, i will have an IR thermometer tomorrow.
Thee shouldn’t be air mixed with the water might be from muffs but would make me think pump is pulling in exhaust gas unless you do not have enough supply volume or pressure.
what is the layout of your cooling hoses to manifolds and elbows. Do you have separate feeds off thermo housing to manifolds and elbows ?
 

svb165

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The hose configuration is what's driving me nuts...... both elbows are teed together and run under the motor to a junction , the thermostat also , everything ties together for the drain system. I don't have decent pics of the junction, its busy under there.
 

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Scott06

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The hose configuration is what's driving me nuts...... both elbows are teed together and run under the motor to a junction , the thermostat also , everything ties together for the drain system. I don't have decent pics of the junction, its busy under there.
This could be an important piece. your manifolds and elbows are fed separately (Warm manifold system). The elbows will get water supplied at all times so exhaust get cooled when the thermostat is not open. Your set up is a little differnt than mine. I have a T on top of the thermostat housing that has two spring loaded balls that restrict the flow to the elbows. If they stick open too much raw water will bypass the block and go right overboard via the exhaust. You have to have some type of similar set up so that raw water get diverted into the block when thermostat is open
 

svb165

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This could be an important piece. your manifolds and elbows are fed separately (Warm manifold system). The elbows will get water supplied at all times so exhaust get cooled when the thermostat is not open. Your set up is a little differnt than mine. I have a T on top of the thermostat housing that has two spring loaded balls that restrict the flow to the elbows. If they stick open too much raw water will bypass the block and go right overboard via the exhaust. You have to have some type of similar set up so that raw water get diverted into the block when thermostat is open
The biggest issue here is, I did the engine swap 9 almost ten years ago.
I ttttttthink I put all that back together correctly but time has me questioning everything. we heard a strange noise on the water as I shut the motor off,, it sounded like something spinning fast then coming to a stop. almost like a bearing spinning to a stop. you could hear the whirring for a couple seconds after the engine stopped..? l couldn't pin point the noise before it stopped the two times I've heard it now. I believe you are correct. I don't believe the water is being diverted correctly as the elbows and manifolds stay cool compared to the motor. I can leave my hand on either riser even as the temp gauge reads 200 and the manifolds I can slowly "slap" bare handed without fear of burning myself.. I'm about ready to remove the entire single knob drain system and plumb it old school.
 
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