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Mercury 402 40HP 1979 model thermostat?

Or look for a bulge on the rear of the powerhead to the side of the cylinders. May be on the top of the block at the rear. Bulge about the size of a US quarter dollar or so. S/N is best bet as race stated.

Mark
 
5365878 is the SN. 2 cyl model. There is apparently a 3 cyl model that exists. Old motor. I wanted to check the thermostat among other things but can't find it.
 
There is a housing on top of the block , behind the flywheel.---thermostat is in there.-----Big red letters on top of this page leads you to the exploded views.
 
Thanks for the info. This boat's owner developed Alzheimers and the boat/motor sat outside with no cover (full of water and moss) for about 5 years. It fires up and runs now after a fuel purge (full of rainwater and rust) but does not pee. I thought I would check the thermostat since it sits in the water stream before pulling the foot. The nuts holding the foot on are shiny and non-painted so the foot has been pulled before. The owner (on medicine now and some better) says the impeller has been changed but can't remember when. His Honda Gold Wing 1100 motorcycle sat out in the rain for 5 years, too. You can imagine what it looks like. He was a big bass fisherman and has the hots to go fishing. He thought the boat was fine and would just "fire up." The wiring harness was completely rotted and I have already changed it.
 
I took the thermostat out and it was caked up with hard deposits. I ordered the parts to replace it. The poppet valve feels springy and looks OK. WHAT does it do? Also, what is the cylinder bleed hose for? Is it part of the water flow or fuel flow? Thanks!!
 
Cylinder bleed hose takes oil / fuel from bottom of engine and pumps it back to the top cylinder to be re-used.
 
On my engine the poppet is inop below 2500 rpm and above that it bypasses the tstat essentially as it lets raw water through the powerhead and is larger in diameter and you don't really need the stat at the higher rpms anyway, so says my serv manual. I know that to be a fact as when I first took my used boat out for the first time, at low speed I got an OT alarm but getting on plane squelched it. Reducing the throttle back to a low rpm caused it to return. Troubleshooting found a stuck shut stat. Changed it and no more alarm at low speed.

Mark
 
Correct , the thermostat is used to control engine temperature at low speeds.-----At higher speeds the water pressure increases , if you have a waterpump in good condition.------The water pressure lifts the poppit valve off it's seat for proper water flow /cooling at higher speeds.----That is why cooling systems must be maintained in good condition.
 
I replaced the thermostat but still no water from the telltale hole. Is there a parts breakdown for the foot so I can order the impeller kit? Looks easy except I'm not sure how to get the shift linkage apart.
 
There is no need to worry about a shift linkage as it is splined.-----Put control in forward and remove the lower unit. ------Make sure lower unit is in forward when you re-assemble.----There may be a hidden screw under the trim tab / sacrificial anode.
 
Got the foot off after getting the prop repaired. It was full of BIG flies all dead. Impeller had 3 broken fins and 3 barely hanging. Did not find any pieces of the impeller. Maybe they got sucked up into the head? I am assuming the drive shaft rotates clockwise looking down on it, and that the impeller blade tips should curve to the left (counter-clockwise). There is a small rubber hose attached with a nylon fitting at the back of the foot. What is it for? Impeller housing had some damage in the center on the nylon top so I will replace that also.
Thanks!
 
The hose may be for a speedometer.---------Driveshaft rotation is the same as the motor rotates.------Put impeller on the shaft and rotate the shaft while pushing the housing down over the impeller.
 
I was going to smear a light coating of marine grease in the housing. Just wanted to be sure how to orient the blade tips. I guess the movement of the driveshaft will force them the right way when the motor starts anyway. Will shoot some compressed air back through the system in case there are bits of the old impeller up in the motor.
 
The manual suggests the regular Merc grease in a tube with teflon, but soap works too. I never liked putting grease on rubber unless it was a grease seal, made of neoprene or similar grease resistant material. Don't know what rubber the impeller is made of and yes if you rotate the crankshaft CW while installing the blades will turn in the correct direction.

Mark
 
I put the boat in forward and removed the foot. After I installed the impeller (damaged), I spun the driveshaft clockwise. It turned OK and the prop turned with it. I put it in my car and went back 2 days later and it is locked up. Hasn't been touched by anyone. The driveshaft will not turn either way. The prop will turn forward with a clicking sound but the driveshaft doesn't turn with it. Prop won't turn in reverse direction. Not sure what is going on.
 
Did you by any chance pull the driveshaft upward when replacing the impeller? There is a pinion gear on the end of the driveshaft, if you pulled it up more than 1/2", it may have popped off. If so you will have to tear down the lower unit to get it back on. I am assuming you have not reinstalled the lower unit yet. If you have reinstalled it, then it is probably jammed and installed incorrectly. Let us know a few more details so we can guide you.
 
I would try to shift it into neutral, forward and reverse with a pair of vise grips manually before tearing anything down.
 
Shifter will move back CCW but not CW. Assume CW direction is forward so should not move that way since I put the shifter in forward before I removed the foot?
 
Driveshaft can not be pulled out or off the pinion, without removing the fastener on bottom of the driveshaft !!---Any water in this gearcase ?----------Bearings may have rusted if it had water in it.
 
Driveshaft doesn't move up at all that I can tell. Everything was turning smooth when I set the foot in my car. I spun the driveshaft a few times after bolted the impeller cover in place and the prop spun around. I checked the foot oil awhile back and it was clean. The foot has been lifted in and out of the back seat of a car and that is all. Can't figure what happened.
 
When the lower unit is in forward then you can turn the prop clockwise and it SHOULD click or ratchet.---That is normal !--------If you try and turn prop counterclockwise it should lock and that is normal when in forward gear.
 
I put some light marine grease inside the housing and some behind the keyway to hold it while I slid the impeller on. Then I spun the drive shaft a few times to make sure the impeller was turning free. Sounds like the prop is doing what it should according to racerone.
 
..."Driveshaft can not be pulled out or off the pinion, without removing the fastener on bottom of the driveshaft"

Correct, though it's been tried!

Jeff
 
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