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1991, 140 hp looper overheating

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pa dude

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I have a 1991, 140 hp looper that overheats at high rpms. I have replaced the water pump and thermostats. Compression is good, have used infrared gun while running it in the water. I was wondering if salt buildup in the cooling system could be the problem by causing poor circulation. Any advice or ideas would be greatly appreciated
 
I was wondering if salt buildup in the cooling system could be the problem by causing poor circulation.
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After 22 yrs of saltwater use it's highly possible the coolant circulation passages are narrowed. Is there a poppet valve on the engine? Did you change it?
 
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I don't know about John/Rudes...someone can chime in here. A stuck poppet can make it overheat at high RPM.
 
As far as I can tell, there are no poppet valves on the 140. I'd guess plugged cooling channels if everything else is good.
 
Are there not 2 diaphragms in there, one at each thermostat ?----Perhaps this needs to be looked at to see if they are in place and if they can pull the thermostat off the seat.----Has the throttle contolled " cooling boost valve " been looked at ?-Definitely needs inspection.
 
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If necessary you can remove the cylinder covers (heads) to view the water passages around the cylinders.
 
racerone said:
Are there not 2 diaphragms in there, one at each thermostat ?----Perhaps this needs to be looked at to see if they are in place and if they can pull the thermostat off the seat.----Has the throttle contolled " cooling boost valve " been looked at ?-Definitely needs inspection.
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Where is this valve located?
 
The thermostats on these (I own an 86 model) are a kinda combination thermostat and poppet valve all in one - one for each cylinder head.

They do get crudded up even in fresh water.

At the end of each season I take the whole assembly out, disassemble it (as much as it comes apart) and soak the whole works in vinegar for 24-48 hours (pretty weak acid eats all the cooties and doesn't harm plastic/rubber/metal parts - plus at under a buck a gallon it's way cheaper than CLR, Saltaway or any of the other commercial solutions that do exactly the same thing).

To clean out the passages I usually do it as follows (at least this is my method).

1) remove the lower unit
2) plug the water tube (at the point where it would go into the water pump housing.
3) remove the thermostats
4) tilt the motor as far forward as it will go
5) stuff a plastic garbage bag followed by a rag up the exhaust (to get a pretty tight seal)
(you want to effectively seal your cooling system - save the open thermostat holes)
6) pour a couple jugs of vinegar into the open thermostat holes - keep pouring until it over flows.
7) leave it sit for a couple of days
8) tilt the motor back to the full down position
9) pull your rag/plastic bag plug out of the exhaust and let her drain
10) unplug the water tube and jury rig a garden hose to and flush for 5 or so minutes
11) note the cooties on the ground after flushing

(Many commercial concoctions will work faster, but as stated, the vinegar works fine if you give it time and it's super cheap)...
 
hi galamb, followed your procedure but notice vinegar leaking from above in the channel where the water tube is located. water should only travel up the tube and out the exhaust, is that correct?
 
hi galamb, followed your procedure but notice vinegar leaking from above in the channel where the water tube is located. water should only travel up the tube and out the exhaust, is that correct?
 
Yes, that is correct - there is a little seal (grommet) where the water tube meets the base of the powerhead. That should be a water tight seal (so you don't loose pressure in the cooling system).

If you have a leak there with virtually "no pressure" from the water pump, you can almost be guaranteed that it's significantly worse when under pressure = "possibly" not enough water getting through to cool the powerhead properly...
 
If you are relatively handy and have some mechanical tools, it's not complicated.

I work mostly on Merc, just happen to own a 140 Ev, so working here from limited memory of when I redid my motor.

The grommet is mounted in the exhaust housing (not the plate which the power head is bolted to). I'm thinking you can get the housing out through the bottom of the leg (with the lower unit removed) - it's bolted in from the underside (threads go into the plate towards the powerhead).

So a bit of jigging around, and a manual would definitely be of great assistance, but something you could do with a socket set and an hour or two of your time.

The grommet sells for about 5 bucks - it would be a shame to pay a hundred dollar service charge (or more) for a 5 buck part...
 
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