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Mariner 60 overheating

M

mvardane

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"I have an ongoing problem wit

"I have an ongoing problem with my 1988 Mariner 60HP 3 cyl. The overtemp. alarm sounds frequently after 5-7 min. above 3000RPM. I have 5PSI water pressure from 1000-3000, and up to 8-9 PSI at WOT. Tattletail is strong and steady. If I back down the throttle when the alarm sounds, it will stop. But when I speed up, it will sound after a couple of min. I have changed water pumps several times over the years, all yield the same results for pressure and temp. alarm. I changed the sensor, but it did not change the symptom. The autoblend was removed from the boat before I purchased it, so I mix gas& oil 50:1 manually. Any suggestions?"
 
"I had the same problem with m

"I had the same problem with my 88 Mariner some years ago. I believe there was an issue or service bulletin about the heat sensor. I replaced it, and then all was well. Maybe you got an "old style" sensor ? But if you got a new one from a dealer, I doubt that. How old is your water pump ? the pressure may be a bit low, I can't remember what mine ran at, but all pressure gauges may read a bit different. If you have a good hard steam coming from weep hole, water pump would seem ok ,,,.? My Mariner was on a Bass Buggy Pontoon, but I replaced the motor in 2000 with a 70 Johnson, then just this week I got a new boat-motor-trailer."
 
"This particular vintage of Me

"This particular vintage of Merc/Mariner does not have a thermostat or poppet valve. The heat sensor is located right next to the top spark plug. The water pump was replaced last year. I typ. replace it every other year. Water pressure is always the same, 5 at low RPM and 8-9 at WOT. Typ. 6-7 at a 4500 RPM cruise."
 
that is what i thought when i

that is what i thought when i could not find it on the parts program

i bet u need to flush your system with salt-a-way or something in that nature
 
"Year before last, I dissassem

"Year before last, I dissassembled the exhaust covers and cyl. cover. Cleaned it well with a small brass wire brush and lime away. Fun job! spray, scrub repeat. It did not change the symptoms at all. Peeking into the spark plug holes, there is no sign of scuffing on the cyl. walls, piston crowns are all nice and black. I change spark plugs every other year also. They are always dark brown and oily."
 
what about checking the o ring

what about checking the o ring again on the impeller housing and maybe the water tube itself
 
O rings and seals on copper wa

O rings and seals on copper water tube replaced in'04 with no change in results. I have had this boat since about '94 and have been messing with this problem since I got it. The only saving grace is that I only take the boat out 5-10 times per year. Definately low usage. I think Monday I may remove the cylinder cover and clean the cylinders again. I'll go through the water pump again just to be sure. This is pump year again anyway. What about a lean-out condition or timing? But that would be a trip to the shop. I don't feel comfortable checking timing at WOT tied to the dock or trailer.
 
"could be lean
to check wot,

"could be lean
to check wot, just hold the throttle open and use a timing light, that will make the trigger base move to wot"
 
Does the powerhead have to be

Does the powerhead have to be running at WOT or can I remove the spark plugs and crank the starter with the throttle lever at WOT?
 
do can check withour running

do can check withour running
pull the plugs and ground them out
use the timing light while holding the carb at WOT
 
"While at the dealer picking u

"While at the dealer picking up an impeller, I asked the mechanic if he had any ideas about this. He suggested verifying timing: mine was advanced 3 degrees beyond spec. I corrected that. He looked up an old service bulletin, and found that there was a different (no longer available) temp. sensor. Orig. was 260, new was 300. The dealer had one left in stock, so I plunked out the $72 for the higher temp. sensor. It seems that the one I purchased a few years back was a 260, not the higher 300. The 300 sensors have a green sleeve on the lead. the 260 sensors have a black sleeve. I also removed the cylinder cover and cleaned the heck out of the cylinders. Got them all back down to cast alum. No more sediment. So with the new pump, new sensor, corrected timing and clean cylinders, I am very hopeful. Weather should improve by early next week. I'll let you know how it goes!"
 
"wow,,, what a journey you had

"wow,,, what a journey you had to take just because the first guy who sold you a heat sensor, sold you the same kind you already had, but no matter, I bet you are good to go now !"
 
"I'm finally satisfied. I

"I'm finally satisfied. I ran it today for almost 2 hours nonstop, no overheating. The motor did not miss that extra 3 degrees of advance, either. It still ran right up to 5800 with the same prop. Top end about 33 mph."
 
I just posted the same issue o

I just posted the same issue on my 60 mariner and just ran across your post. This sounds like the exact problem I am having ever since I purchased my motor 8 months ago. Mine over heats at 4000rpm. Thanks for your help....
 
"Jerby: Make sure your temp.

"Jerby: Make sure your temp. sensor has a green sleeve over the tan wire. This is the 300 degree sensor. If your sensor has a black sleeve over the tan wire, it has a 260 degree sensor. That 40 degrees made all the difference in the world for me. I don't think mounting the sensor 1/2 inch away from the spark plug on the cylinder was the brightest idea Merc/Mariner had. The spark plug is supposed to run at about 500 degrees or so for proper combustion. Internal combustion temp usually runs in the 600 to 800 range on a good running motor. Kind of hard to put a 260 sensor in that location and keep it from tripping."
 
I have a 94 60hp mariner that

I have a 94 60hp mariner that has less than a season on new impeller pee's great and isn't hot but temp. sensor going off and water coming out of foot is hot.What causes this?
 
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