Temperature Issue Full Throttle

[Themanofsteel]

I installed a 1983 mercury 150hp V6 on my Bayliner Trophy 21' bcuz the other engine blew out. It overheats at maximum/full throttle which is about 5000 rpms. I've replaced the Head Gaskets, Divider Plate Gasket, Thermostats, Impeller, Pop-it, Hoses. I inspected the water jacket and just about everywhere water flows. Still overheats at full throttle.

This engine was too short for my boat so I bought an extension for the mid-section and all the other necessary extensions parts. After exhausting all possibilities so far, I'm now wondering if the extension puts the lower unit deep enough to get sufficient water. See attached side view of the lower units position to the boat. The pic is pretty accurate as to the position. Can anyone tell me if its deep enough.

 

[Chris1956]

It looks plenty deep enough. You should observe the depth of the water while at cruise speed to make sure. Also, a water pressure gauge is a real good idea for all OBs.

Me neighbor has a 200HP Merc motor of about the same year and it is also overheating at high speed. I would be interested to know what your issue turns out to be, since it could help him.

 

[Themanofsteel]

Could the Carburetors have something to do with the overheating? Since I've checked everything else, not sure what else to look at. Can I run it without the thermostats? Would that help with water flow?

 

[jimmbo]

Do not run that engine without the stats
When you had the heads off, did you check them for warpage?
When you replaced the impeller, was the old one intact, or were parts of the vanes/blades missing/broken?
it is possible that the temp sender(s) is closing too soon, you should remove and test/check it.
Did you ever see the engine run before you extended the leg length?

 

[Themanofsteel]

I did not check for warpage. Didn’t think to.
The impeller was intact as far as I can remember. I didn’t notice chunks missing from it.
This engine was on another boat that had been sitting for a very long time. The previous occupant never ran it and had it sitting for at least 3 years. I’ve didn’t see it run prior.

This engine use to overheat at 1500 RPMS. I changed the head gaskets and replaced the popit diaphragm. Since then it only overheats at 5000 RPMS.

When it overheats, the engine is pretty hot to the touch. But I’m not sure how hot it should be. I’m going to install a temp gauage to read the temp.

Could hydrofoils help with the water suction, if that might be the problem?

 

[jimmbo]

When you replaced the impeller, what other parts of the waterpump did you replace?

 

[Themanofsteel]

The housing if I recall and of course the gaskets.

 

[Themanofsteel]

So I tested the Temp Sender. The current sender sets off at around 160 degrees. I bought a new one and it sets off at 200+ degrees. Does tht sound right. Does this engine run that hot? Just want to be sure.

 

[jimmbo]

No it normally doesn't run near 200, but it can run at 160, even a bit higher. Max operating temp will vary due to ambient temp, water temp, load on engine, and water pump and water jacket condition. 200 is still below the boiling point at most altitudes these engine will be used, and it is not hot enough to cause oil failure. In reality, a raw water cooled engine will survive longer if the cooling water stays below 135. at temps above that the salts that are dissolved in the water start to come out of suspension and will eventually build up in the water jackets, Extreme cases look like someone filled the jackets with Concrete and let it set

 

[Faztbullet]

Temp sensor on that model closes at 180-200 and opens at 160-180 and below....make sure the plastic "p" indicator is in place as its a restrictor.

 

[Themanofsteel]

Seems like the overheating is getting worse. Now it’s overheating at lower RPM’s again. The water at idle is pretty hot. I looked at the Poppet again and it’s looks good. Could 1 of the thermostats not be opening. They were new. About 6 months old.

 

[Themanofsteel]

Just tested both thermostats. They seem to open fine. Can’t figure this out. This is frustrating.

 

[Themanofsteel]

Where would I install a Pressure Sensor on my engine. 150 Merc. 1983 V6 Blackmax.

 

[Themanofsteel]

I feel like something is blocking the flow of water. There are 2 little drain holes in the pic. attached. Intermittently the hole on the left stops draining like in the picture. Sometimes its a steady flow, other times it dribbles, and sometimes nothing comes out like in the picture.

 

[Chris1956]

Water should exit that motor thru the gratings above the antiventilation plate and thru the prop. It should also have a telltale, however, a lot of the V6 Mercs do not get a telltale, until the 'stats open.

The poppit valve should open at about 2000RPM, under increased water pressure. You should see the water increase.

The water exiting should not burn your hand, but will be warm. OBs usually have about a 140*F thermostat.

I see some corrosion or other stuff on the motor. You might make sure the water intake grating is clean. On my Mercruiser (left in salt water), the barnacles liked to nest in the water intake passage. I had to scrape 'em out periodically.

 

[jimmbo]

Barnacles can really FUBAR an engines cooling system

 

[Dukedog]

Where would I install a Pressure Sensor on my engine. 150 Merc. 1983 V6 Blackmax.

on top of tha block behind tha flywheel you will see a 3/4" pipe plug.. remove it and reduce down to 90* fitting that fits tha water pressure gauge hose/tubing.. ace hardware is your friend for those reducers/fittings...

while you have tha pipe plug removed start motor and check for water flow from that hole..

 

[Themanofsteel]

on top of tha block behind tha flywheel you will see a 3/4" pipe plug.. remove it and reduce down to 90* fitting that fits tha water pressure gauge hose/tubing.. ace hardware is your friend for those reducers/fittings...

while you have tha pipe plug removed start motor and check for water flow from that hole..

Where can I find the sender to screw in? Also a gauge. Recommendations.

 

[jimmbo]

http://ww2.iboats.com/Boat-Parts-Ac...er.prod_name?q=water pressure gauge kit&s=sol

 

[Faztbullet]

Temp gauges can cause ghost problems...install a pressure gauge. If you do decide to install a temp gauge use the correct style for a outboard...they have no degrees on them just a C and H