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43 running hot

sharkin95

Regular Contributor
"I have 4.3 merc I/O 1995.Runn

"I have 4.3 merc I/O 1995.Running 180-190 under power (3000 rpm) replaced the alpha 1 raw water pump,replaced the sensor, and the gauge.checked with sears laser tool and the hottest point(170)
is at the engine mounted water pump,risers (100)thermostat housing 135-140,I know the problem is lack of water but where?"
 
Could be engine water pump.

Could be engine water pump.

Problem may not be incomming but OUT GOING water is bieng restricked. This will cause the same overheat condition.

Also if you are sure of a incomming water issue it could also be the water hose at the gimbal housing.

Also who replaced the outdrive water pump?

What was replaced? All or just some of the parts?

A clear hose from the transom to the thermostat housing will tell if you are getting air in the incomming water supply.
 
I'll check the flappers to

I'll check the flappers today and do the outdrive water test by pulling off the raw water hose and filling a gallon bucket.my guess is the engine water pump.Every thing else is running cool....
 
""Problem may not be incom

""Problem may not be incomming but OUT GOING water is bieng restricked."

I agree w/Kghost on the restricted water outlet. Have the exhaust mans., risers and elbows ever been removed for cleaning of rust, scale and mineral buildup? They may look OK to you but there are unseen areas that are the problem."
 
"Both risers are 1-2 years old

"Both risers are 1-2 years old. manifolds were cleaned.just to add some info,in May of this year I noticed on the muffs the temp would rise to 165 which it never rose above 160,from May to July she stayed around 165 then I took a trip to Marthas Vineyard in early august and on the way back it stayed at 170 so the problem progressed from May to August that's why Im thinking mechanical.Now at 2500-3000 rpms it's 180-190"
 
Pull off the water inlet hose

Pull off the water inlet hose inside the transom. Look inside the pipe that goes thru the transom for blockage. There have been several postings this summer showing plugged pass thru pipes.
 
I'll check it today.will l

I'll check it today.will let you know tonight after checking raw water flow from o/d
 
Jim

One problem that would


Jim

One problem that would show up after installing a clear hose from the transom to the thermostat housing is excess air bubbles in the water stream or even lack of water flow.

The bubbles would be a result of

torn gaskets at the water pump (outdrive)

missing fat thick square rubber oring on top of pump housing (outdrive)

upper plastic housing above water pump (where the copper tube goes into) leaking or heat damaged.

just some other possibilities.........
 
"well good news and bad news.t

"well good news and bad news.took off the raw water hose to tstat housing ran it up to 1500 rpm's for 30 seconds a ton of water came thru filled a 5 gal bucket,so that tells me no blockage from the o/d to the tstat housing.checked flappers... intact,took off the engine water pump,no blockage thru the block that I could see anyway,came home with the pump took the back plate off,brass impellar looks good and spins tight but freely.bad news is the only thing I can think of is head gasket or exhaust manifolds"
 
There is a 1/2" bypass hol

There is a 1/2" bypass hole inside that can be felt with a long finger from the T'stat seat. If it gets too big then more cool water goes to the exhaust.
 
"I thought about the tstat hou

"I thought about the tstat housing being the problem so I got a great deal on e-bay for a new one (100).there was another thing that eliminates some things I did a compression test and found 135-150lbs 150 being #6 and I have a dash mounted vacuume gauge mounted in my boat for tune up and engine malfunctions,it reads a very little fluctuation from 15.5-16 hg.no milky oil and plenty of power.So it seems just water flow related."
 
The tstat housing and the mani

The tstat housing and the manifolds are the original equipment.The manifolds I had cleaned but not the tstat housing.the engine mounted MEI water pump is 2 years old.
 
Can you post a pic on the engi

Can you post a pic on the engine circ pump impeller.cold manifolds and risers and a hot motor is a circ issue more than a clog issue. Thinking the vanes are missing from the engine pump.
 
"good thought,I took the back

"good thought,I took the back s.s. plate off and removed the plugs all vanes intact and no water intrusion that I could see anyway ,that was my initial thought not enough water flow.My thinking on eng.mnt.water pumps is if the vanes aren't broken and no water enters or exits the weep hole it's fine.It has to turn being on the pulley.I think you and I are on the right track with the tstat housing."
 
"Jim, for what it's worth,

"Jim, for what it's worth, my engine is overheating and the circulation pump had a hole behind the inpeller. I couldn't see it until some of the guys pointed it out. My pump neither squealed nor leaked and the ball bearings didn't feel bad but sure enough it wasn't moving enough water. I still have the overheating problem though."
 
"hi bob:
Thanks for the info.


"hi bob:
Thanks for the info.Being around boats and doing my own repairs I took the precaution of ordering a sierra water pump,you are right the possibility still exist that the pump could not be moving enough water which is what I think is happening.My experience has always been if you have a raw water cooled engine and it's overheating it's usually mechanical.I should have all parts by tuesday ready to install."
 
"Well went out to the boat tod

"Well went out to the boat today and changed the thermostat housing (still waiting for the water pump)the passages were clear but rusty,maybe 1/8"-1/4" of scale the 1/2" hole that is suppose to be up inside where the tstat sits is either non existant or closed this is the original tstat housing.checked both riser's and manifolds...open but very rusty.So I'm hoping it's the engine mounted water pump.trying to get thru till october but exhaust manifolds will get the acid dip."
 
"did all that work and look wh

"did all that work and look what it was.....water pump was good,thermostat housing could have been changed but was ok for now....lack of water... water pocket rubber seal was out and the inner seal was broken.If anyone has a problem they can't figure out for running hot or overheating check this thread first....(overheating at low rpm)rick haverick.thanks to all for the help.."
 
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