Runnin hot...bah!

Tin:

What makes you think head gasket is bad if compression is good all around?

If water is getting into a cylinder then high water pressure could be understood due to compression stroke, but you said plugs are not steamed clean, nor is compression bad. so I don't understand why you think head gasket?

With all the bad head gaskets I seen, water always gets into the cylinder on the power-stroke at least when compression drops and vacuum is formed. Never seen a bad gasket that only flowed one way.

Bite the bullet, it's most likely going to be under the power head in the poppet's

Kamikaze
 
I know it's NOT the head gaskets, think you misunderstood my post. I have a couple more things I want to try before removing the powerhead, but I do believe I will end up removing to find the blockage.

I can run all day @ 30-32 mph without a problem, it's when I go over 4000 rpm's, which I really don't do, when I get an alarm. But I need to find the problem cause it just ain't right :-/
 
Tin:

Roger - I miss understood, although I have an idea that is off the wall but may just help verify what the problem is.

Temporarily remove the water hoses from the top of the heads and block as shown in the picture in your earlier posting and connect a new temporary drain hose with a manual on/off valve that is rigged to drain over the side. Run with the hood off and at speed open the valve. Verify water pressure drops and alarm no longer sounds. ( You should be by passing any blockage that may exist under the power head and the water flow should cool the motor as intended. At least then you'll know it's a blockage for sure vice a faulty alarm or something else inducing the problem.

Kamikaze
 
Tin Man, your first post said the temp gauge was showing 145-150, make sure you're chasing an overheating problem and not a grounded out sensor wire. Disconnect the over heat temp switch wire( tan/blue stripe)at the sensor, run the boat and see what happens. The alarm wokrs off of a ground circut, anywhere in the harness, if the wire becomes grounded, it will set the alarm. If the poppet valve is removed, the block will not fill with water completely and create steem pockits. I wouldn't even bother with pulling the powerhead or lower unit till I confirmed the problem is high temp, and not a wireing problem.
 
It's a PITA because I can't create the problem at home, needs to be running in the water at 4k rpm's plus. It's the PRESSURE and ALARM that makes me think there's an obstruction but I will verify it's not the sensor before I yank the powerhead.
 
Most marine dealers can flush your cooling system and remove any buildup of junk in the water passages. Are you getting water out the pee tube at 140-150. If it's like my Merc 150 you won't.
 
I had a similar problem on a 83 150 Merc. It turned out to be a broken ring in the middle port cylinder which is just below the temp sensor. I pulled the power head to check the gasket between the base. changed head gaskets and had the heads shaved, etc. While the heads were off ,I was looking up in the cylinders and noticed the ring gap on that piston was about 1/4 inch.
Good Luck.
 
phatdaddy said:
I had a similar problem on a 83 150 Merc. It turned out to be a broken ring in the middle port cylinder which is just below the temp sensor. I pulled the power head to check the gasket between the base. changed head gaskets and had the heads shaved, etc. While the heads were off ,I was looking up in the cylinders and noticed the ring gap on that piston was about 1/4 inch.
Good Luck.
Click to expand...

pd, did you have good compression?
 
Tin,that was the weird thing, I did have good comp on all cylinders. A mechanic friend said the end of the ring must have broke off and passed out the exhaust. The wall of the cyl looked good. I had some other issues with the engine, so I just re-powered instead of going any further. One thing I did learn is to check your t -stats. I change mine every year w/ the water pump. I take a piece of string and put it in the opening of the t-stat and hang it in a pot of cold water. Put the pot on the stove with a frying thermometer. Turn on the heat and watch the water warm up, when the t-stat drops in the pot, that is the temp it is opening. I have found them to be as much as 20 degrees off. I also like to get two that open about the same time.
 
pd, what about your water pressure?? I can't see that being high with a bad ring.


I just read the other day about that t-stat test...mine are new.
 
I'm 90% sure it's an obstruction. I'm going to check the waterpump and housing...it's possible I cracked the housing (maybe over torqued) when installing the new impellor and I'm sucking air. If that's not it I'm going to remove the...what the hell is that cover between the heads called again???

I don't think it's a major engine problem....she runs like a raped ape! :o
 
Tin , you're right, the broke ring would not have anything to do with high pressure. My pressure was 12 to 14 lbs @ 4000 rpm. The only symptoms I had were after running at 4500 rpm for 25 to 30 minutes, the temp alarm would go off, but the gauge only showed slightly above normal. I would stop the boat and turn off the motor. After 1 minute, I could crank it up and run another 25 to 30 minutes.
I would still test the t-stats, even though they are new. I've had brand new ones out of the box be way off . I've also had better results with OEM water pumps & t-stats than "will fits".
 
i found this LU exhaust seal all busted up on mine...think this could cause my overheat alarm? i got one on order today but it wont be here till next week sometime...now i got to wait to see if the new water pump fixed it...or should i just put the LU on with this seal like it is and run it?

mycamerapics034yt9.jpg
 
Kajun, the mechanic thought that my seal was bad, he said the exhaust would pre-heat the water before it go to the block and cause higher than normal running temp and maybe overheating. Unfortunatly, my gasket was O K .

Tin, I might have missled you with my first post. I never did get the motor to run normal. I lost a season and spent $1,000 on "repairs". I did everything my shade tree experts suggested and finally took it to the local dealer. A week and $700 later he called and said he got it running "cooler". The only thing he noticed was the broke ring. By that time I had had enough, I loved the V-20 hull and wife said life's too short and she missed a summer on the water( She was a teacher then so we took it out 4 or 5 times a week), so I put a new motor on. That was 12 years ago, so I'm due to make that decision again soon. I don't think you have the same problem because of the high pressure symptom
 
Re: Running hot...bah!

Kajun:

Given the corrosion on the lower part of your engine bracket have you given any thought that you might be overheating due to salt build internally within the engine cooling jacket? I have used MST Flushclear
( http://www.mstguardian.com/Treatment.htm and found it quite effective at removing salt build up.

It looks like the company is having some trouble with an employee patent issue, but they might still be selling the stuff? It is rather easy to do with the lower unit already off, just mix the stuff up, fill a pressurized 3 gallon bug sprayer and connect it to water pump tube in the midsection with a rubber plug and fill the engine cooling jacket, let stand for 15 minutes and salts all gone.

Kamikaze
 
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