Home › Forum › Ask A Member › 1957 Merc Mark 25 not warming up
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GUY SCHMIDT.
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December 5, 2023 at 2:34 pm #283043
Started above motor for first time after purchase. Ran in barrel for several minutes. Head getting warm to the touch but tell tale stream still cold. Is this normal .
December 5, 2023 at 4:13 pm #283048how warn medium warm burning warm ???
did you replace the impeller and gear oil …first thing to do on a new ..motor
tell tale may not always include cooling water it may be sent down the exhaust housing nowhere to be seen ..and out the prop the tell tale tells you the pump is pumping
can you meaure the PH temperature with a IR gun
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December 6, 2023 at 3:54 am #283058I’d say low to medium warm. And I wasn’t the guy who rebuilt it. I was wondering if there could be blockage that diverts the water out the tell tail and doesn’t cook the engine?
December 6, 2023 at 7:41 am #283059no thermostat expert but in general water always go right back out via the tell tale and the thermostat only allows new cooling water to be circulated around the cyl jackets by releasing the jacket hot water when the temp exceeds around 140 deg.
in the attached diag. on a OMC engine tell tale water would get warmer after a while. since your’s does not I suspect Merc’s dump it down the internal exhaust housing…to also provide cooling
if your engine ever gets burning hot then there is a problem. A cheap IR gun will tell you the temp on the PH and a hot spot would indicate blockage needing attention
If not a stuck impeller blade it could be just accumulated sedidements which you can flush out with commercial products.
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December 6, 2023 at 11:16 am #283062No thermostat on a mark 25]
December 6, 2023 at 11:44 am #283063there you go then … even simpler extra cooling needed or not ! May explain why tell tale is cooler than expected !
thanks for clarifying.
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December 9, 2023 at 2:57 pm #283125You should be able to hold your thumb near the top of the block while it’s running. If you can’t, it’s too hot. (Don’t forget the moving flywheel.)
Long live American manufacturing!
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December 9, 2023 at 7:41 pm #283136Thanks again for your time and help
December 11, 2023 at 8:29 pm #283165Guy,
I had cooling problems with a KF5 very similar to the mk 25. I pulled the water jacket cover off the cylinder, has no head., very carefully, the bolts break easy, used a torque wrench, using max touque in rweverse as to not use excess torque rating & a little heat on the cylinder threads& panther piss to loosen to get them out.
then used anything that woulld fit in the cylinder cooling passage to scrape the surfaces clean then hose out & removed a large amount of junk from the area. Next I reversed thru the water release hole where the discharge is to clear that passage, then put back the water jacket cylinder cover. NEVER scrape the cover or cylinder top as it will leak if you do. Install new fasting bolts or studs so next time you remove only nuts to service, MUCH easier, use stainless studs & steam pipe thread lubercant, comes in a small tube like toothpaste to insure removable, looks silver paste. The water exits from the wateer pump up a copper pipe up the leg to the water passege into the exhaust cooling side cover & fills that passge then the cylinder cooling area then exits thru the exit passage & a weep hole inside the leg to cool the exhaust. Very important to keep the bottm crankshaft seal good as the water exit is next to exhaust outlet. The seal is placed downward so inportant because any unburned fuel inside the crankcase is pushed out into the leg to keep from fuel collecting in the crankcase. I also have seen broken blades from the waterpump stuck in the watertube in the leg so it would impede water flow, Also on some watertubes the bottom cut were cut flat & if they vibreae down very little & impede water flow. Mercuy found this mistake early & started cutting the water tube at a 45 degree angle. It’s worth it to pull the powerhead, replace the base gasket & bottom crankshaft. You will know if the top crankshaft is bad as fuel vaper will soak the mag & no spark. If you do the top seal , (I would) Get a pitman arm remover & dremel it to fit the magnetic rotor to remove the roter to remove the magneto plate to get at the top seal, two screws going sideways for plate tension. Clean & relube friction surfaces, use an inert light grease. Crankshaft seals are like shoes, never install one, do the pair! Your idiling will improveSO much & save your rod bearings from sucking discharge water into the crankcase!!! P.S. The drawing shown is for OMC (Evinrude & Johnson motors). Mercury has no head or gasket, only a cooling waterjacket cover. The pistons install from the crankcase up because the cylinders0n were machined as one piece. I guess because of high compression Carl thought they would blow head gaskets, so he made them one piece & resolved the possable problem, in my opinion. Who’s Carl??? anyway?
Good luck
December 19, 2023 at 8:02 pm #283356Guy,
I had cooling problems with a KF5 very similar to the mk 25. I pulled the water jacket cover off the cylinder, has no head., very carefully, the bolts break easy, used a torque wrench, using max touque in rweverse as to not use excess torque rating & a little heat on the cylinder threads& panther piss to loosen to get them out.
then used anything that woulld fit in the cylinder cooling passage to scrape the surfaces clean then hose out & removed a large amount of junk from the area. Next I reversed thru the water release hole where the discharge is to clear that passage, then put back the water jacket cylinder cover. NEVER scrape the cover or cylinder top as it will leak if you do. Install new fasting bolts or studs so next time you remove only nuts to service, MUCH easier, use stainless studs & steam pipe thread lubercant, comes in a small tube like toothpaste to insure removable, looks silver paste. The water exits from the wateer pump up a copper pipe up the leg to the water passege into the exhaust cooling side cover & fills that passge then the cylinder cooling area then exits thru the exit passage & a weep hole inside the leg to cool the exhaust. Very important to keep the bottm crankshaft seal good as the water exit is next to exhaust outlet. The seal is placed downward so inportant because any unburned fuel inside the crankcase is pushed out into the leg to keep from fuel collecting in the crankcase. I also have seen broken blades from the waterpump stuck in the watertube in the leg so it would impede water flow, Also on some watertubes the bottom cut were cut flat & if they vibreae down very little & impede water flow. Mercuy found this mistake early & started cutting the water tube at a 45 degree angle. It’s worth it to pull the powerhead, replace the base gasket & bottom crankshaft. You will know if the top crankshaft is bad as fuel vaper will soak the mag & no spark. If you do the top seal , (I would) Get a pitman arm remover & dremel it to fit the magnetic rotor to remove the roter to remove the magneto plate to get at the top seal, two screws going sideways for plate tension. Clean & relube friction surfaces, use an inert light grease. Crankshaft seals are like shoes, never install one, do the pair! Your idiling will improveSO much & save your rod bearings from sucking discharge water into the crankcase!!! P.S. The drawing shown is for OMC (Evinrude & Johnson motors). Mercury has no head or gasket, only a cooling waterjacket cover. The pistons install from the crankcase up because the cylinders0n were machined as one piece. I guess because of high compression Carl thought they would blow head gaskets, so he made them one piece & resolved the possable problem, in my opinion. Who’s Carl??? anyway?
Good luck
Thanks, I didn’t see your message earlier and wasn’t on line for a bit. Great info.
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