overheating

[bbohanek]

Hi Folks, first time on this web site. although I have found some Q & A on overheating I thought I would post my own.

I have a 1974 351w that is over heating 200+ degrees.

I have had it in the water 10 minutes in the last two years.

1. bought a used 1974 351w and installed (was suppose to have 30 hours on it) not sure of that in hind site and the old guy who sold it to me is deceased.
2. replaced manifolds and risers log style (mercrusier)
3.replaced temp sending unit.
4. had gauge tested (good)
5. replaced thermostat (stock 160)
6. supposedly the (bad, bad bad) mechanic I had install the motor replaced the raw water pump impeller in the mercrusier R type out drive.
7. replaced hoses.
8.circulating pump is tight, no noises, no slop
9. get water out of sterndrive (not sure what is the proper amount) you can hold your hand under it, it is hot but not uncomforatbly so.
10. you can place your hand on the manifolds but not the engine.

Any thoughts on why it running so hot?

A couple of more things, the risers and manifolds where replaced with mercuriser, the thermostat housing is still the OMC one that was on the engine when I bought it could this cause a problem?

How do I test the impeller? I get water flow when I put the muffs on it, but isn't this forcing water into the system? should I remove the prop and place the sterndrive in a garbage can filled with water?

this is getting fustrating any help would be appreciated.

brian

[bbohanek]

Nobody on the whole net has an answer? No wonder I am feeling fustrated here. Any thoughts would be appreciated as I am new to boats and have no experience on boat mechanical problems and how to diagnose them. The boat is a 1973 formula 233 with a 351w and a mercrusier pre alpha outdrive.

[StianM]

Did you check that there is actual water circulating in the engine?
You have fresh water colled block and sewater colled heat exchanger right?

[bbohanek]

I have a raw water cooling system with no heat exchanger. The only way i thought I was getting circulation was that I have water discharge.

If I wanted to do an acid flush should I somehow by pass the raw water pick up. I do not know if it is ok to put clr or muratic acid through the outdrive.

[StianM]

I would guess your system is coroded so there will not be enough hear transfere from the block to the water.

I have no idea actually since I have only ben dealing with systems that have heat exchanger and would newer use annything else eather.

[bbohanek]

new question: i put the outdrive in a trash can and ran the motor, intially water was coming out of the exhaust then it stopped after about a minute? any ideas? now I dont know about the impeller that was suposedly replaced? Maybe I will go pull the inlet hose on the inside of the boat? Any thoughts?

[StianM]

Did you try again and it hapend over and over again?

I don't know this engine. Is the belt to the waterpump sliping or do you have a water filter where water føows trough, but stops after various dirt has cloged it? Maybe it fall down after you stop so it only clogs it after a some running.

The best way to find out is the elimination method.
Find out what is not wrong and take it from there

[bbohanek]

the water from the raw water pick up pulsates out ? is that normal? what i mean is i disconnected the input hose on the hull side while the motor was running and the water came out in a lame stream then stopped then a stream then stopped then a stream. Is that how the water is put into the engine?

[Pevito2]

I have a mercruiser 351W engine, and i´ve been through that a while ago, perhaps i could help.
You must have water flow to cool your engine. Any restriction will lead to overheating.
This pattern off water flow you described is correct. i saw it in my boat. When disconnecting the fresh water ( the one that brings cold water from the outdrive) from the termostat housing and point it upward, it must throw water 2inches height. If it passes this test, you have a good impeller and raw water pump.
You should now check for restrictions. The risers , as you replaced them must be good. Do you have power steering ( I don´t)? I know , at some point on it , that pieces of old impellers and debris could get entrapped, and restrict water flow.
Removing the thermostat valve for a quick trial, to see how it responds will not be harmfull, but you must reinstall it after.
If you have a hot engine and not as hot exhaust manifolds, you could have a restriction on the engine block, or a bad water circulating pump. I don´t know what kind of thermostat housing is yours but they usually have bypass that allow directly water flow to the manifolds.
New water circulating pump is cheap insurance, they cost $49 at ebay ( be sure it is marinized, with brass impeller),are easy to change, and a common souce of trouble, mainly on open systems.
If you have checked all above, and are sure you have good water pump, good circulating water pump, good hoses, good riser, exhaust manifolds, no restrictions on the periferals ( have you checked exhaust , at the drive, where the fumes come out?) then you have a restriction inside the block. Likely in old blocks , with open cooling stems, that runned on salt water. Hot salt water is extremely corrosive , and can also cause the salt to cristalize inside the block, specially if it runs too hot. I don´t have expecience with flushing solutions to clean the water channels inside the block, but at least you know where the problem is.
Hope that helps. Good Luck

[bbohanek]

it was the circulating pump.. Thanks to those who replied.