1965 9.8 Merc overheating

I have exhausted previous posts looking for this, not satisfied, so here is my question. I have a 1965 Merc 110 9.8 HP motor. It runs great for 5 minutes or so, then starts to get hot. Tattle tail stream is intermitent at times. I removed the flush plug on bottom of pan and good water flow comes out while running. Still heats up. Compression is a solid 115 psi on both cylinders. I tried flushing block every which way, does not seam to help.
Dont want to remove block covers for fear of snapping off bolt heads. Any ideas ? Thanks!

Re: 1965 9.8 Merc overheating

When is the last time you replaced the impeller?

Re: 1965 9.8 Merc overheating

last week

Re: 1965 9.8 Merc overheating

Have you tried to see if there is anything blocking the outlet from the tell tale by shoving a piece of trimmer cord up there? Mud daubers love those places.

You said that you had good flow by opening the flush plug but that is before the cylinder head, is it not?

Is this engine operating in salt water?

Where does water exit when you try a flush through the flush plug?

Gerry

Is this engine operating in salt water?

Re: 1965 9.8 Merc overheating

Dont know the history of this motor, I am inland, dont beleive it has ever seen salt water. No rust anywhere. I shoved small .100" flex cable into pee hole and worked it around, I do get a fair amount of water out the hole when running, but it is not always constant, it will stop then start again, but soon motor starts steaming etc.
The flush plug is on opposite side of block from pee hole, definitely seems like something is blocking flow. I will probly have to remove covers, but I know that will not be fun snapping bolts.

Re: 1965 9.8 Merc overheating

It sounds like something (old impeller blade?) is blocking water flow, you can take the powerhead off the driveshaft housing and see what's there. You don't have to remove the water jacket cover if you find something there; and check the water tube that goes from the LU to powerhead with the flush device.

Re: 1965 9.8 Merc overheating

Well, you gave me another option, still sounds like pulling teeth, havent much experience pulling powerhead from leg, or at least not putting one back together.
Thanks for you help, I cut firewood all day today, Ill have to tackle it maybe next week.

Re: 1965 9.8 Merc overheating

I pulled LU and reflushed block. I put a hose on the pipe and opened the flush port to backflush this thing, a lot of water coming out of pee hole and flush port. Also water is coming out of driveshaft housing. Is water supposed to come out of housing or do I have a breach up above pipe ? Thanks

Re: 1965 9.8 Merc overheating

When going after fasteners that have a history of being stubborn, consider PB Blaster or Kroil. A little squirt goes a ong way and usually helps.
Good luck.

Re: 1965 9.8 Merc overheating

Congrats on your first post ! This site is very helpful. I use kroil, but bolt heads get soft from galvanic corrosion, and if one breaks you can bet the rest will.
I hope someone can answer question in my last post.

Re: 1965 9.8 Merc overheating

shadow;

I am trying to picture what you are doing and it is probably my age. Are you saying that the LU is removed from the gear leg (driveshaft housing) and that the water tube is still in the leg and that you have attached the water hose to the intake end of that tube, where it would normally attach to the top of the waterpump?

Therefore you are now pumping hose pressure directly up the water tube into the powerhead but you have water coming out of the inside of the leg as well as the pee hole and the flush port.

Depending on the pressure you are putting up the tube into the engine passageways, I would expect the volume of water to exceed the ability of the powerhead passageways to handle it, therefore you are geting an excess leaking past the seal at the top of the water tube and spraying the inside of the leg.

If that is the case, just try again by very, very, slowly increasing the water flow just until you have a reasonable flow through the pee hole and the flush port and stop turning the tap at that point. This flow should pretty closely equate to the normal impeller/water pump flow/pressure,

Do you now have an excess of water leaking and if so, from where?

Gerry

Re: 1965 9.8 Merc overheating

The majority of cooling water exits down the torque tube, and your hose has much more pressure than the engine pump. The engine is plugged either behind the exhaust plate or between the exhaust cooling passage and the engine water jacket which will mean removing the water jacket cover also.

Re: 1965 9.8 Merc overheating

Gerry,
You have it right, water spraying back down leg. Is this not good ? I will have to resume working on this tomorrow, & try your suggestion.

Re: 1965 9.8 Merc overheating

shadow;

I am just saying that doing the test the way I suggested will act more like the water pump impeller. If you have too much pressure by turning the tap on several turns, the volume of water at the entrance to the powerhead will exceed the capacity of the internal passageways and it will have to relieve itself somewhere and that will probably be at the top of the water tube where it is sealed into the powerhead. That excess will flow down inside the leg.

I'm not too sure I understand Laddie's comment as you say you have good flow out the pee hole now.

Let us know what you find out tomorrow.

Gerry

Re: 1965 9.8 Merc overheating

Weather is lousy here, may be a few days before I can get to it. Will post back when I do.

Re: 1965 9.8 Merc overheating

Carholme, if you had a clue how the cooling system on the engine worked or ever had one apart you would understand my post.

Re: 1965 9.8 Merc overheating

No need to get stroppy, all I said was I did not understand your comment. If the poster came on this forum and said that he had good flow out of his engine pee hole, would you tell him to first remove the water jacket?

shadow;

I'll let Laddies get you sorted out as he obviously feels that I am not qualified to help. All the best,

Gerry

Re: 1965 9.8 Merc overheating

I appreciate Laddies opinion and Carholmes as well others. I will listen to all and decide for myself which avenue to persue. As I stated earlier, I am not willing to remove water jacket unless I everthing else fails. I dont want to end up with a pile of scrap metal with good compression and unrepairable water jacket ( broken studs). I am a machinist by trade, so maybe I have a loathing for removing broken studs. Sometimes it works other times it's futile.
All I know is that this forum makes it more fun working on these old outboards. Thanks again to all who take the time to reply.
Ted, (Shadowrider)

Re: 1965 9.8 Merc overheating

Laddies,
From what you said in a previous post ("The majority of cooling water exits down the torque tube, and your hose has much more pressure than the engine pump."), it is normal for water to exit from leg, I assume I did not blow any gaskets or seals by doing what I did ?

Re: 1965 9.8 Merc overheating

No, I don't believe so the water you saw coming out of the center section was coming out of the exhaust cooling port. This may help wish I could find a picture of the exhaust side of the engine to show you how it works but I guerss I will try to explain it.
First a couple of facts about cooling system of the 10 HP and less engines

1. The telltale is not the cooling water exit, probably 90+% goes out with the exhaust, the water out of the telltale simple lets you know the pump is working.
2. When ever a impeller fails you must find the impeller bits that have broken off, if they are left in the cooling system after the repair, when the engine is started the water flow will push them to a restricted spot in the system and plug it up. There is no way to dislodge them with air as they were pushed in with the water hydraulics. Blowing through the water pipe or telltale can not remove them as the water exit passages have more volume than either place.

After the water leaves the pump it travels up the water tube to the lower cowl , at that point there is a rubber grommet sealing the tube to the cowl which seldom gives trouble but on engines after the serial #1742746 there is a nylon washer on top of the grommet which melts on a overheated engine and limits water flow.. Engines with a flush on the cowl will have limited flow at the flush, when this is the problem. At this point there is the powerhead gasket which I have never found one leaking, the water makes a 90 degree turn and goes to the exhaust cover for pre warming after warming it travels thru passages thru the exhaust divider plate into powerhead cools the engine and is dumped into the exhaust at the bottom of the exhaust divider plate and out the lower unit. Normally impeller parts are found in the area of the exhaust cover but when we do a engine with this problem e will take the time to check the nylon washer, exhaust cover and the passage into the power head which means removal of the water jacket cover to be sure. It?s much easier than taking it apart a 2nd time.