Running hot at low speed

[rock doc]

Some history. I had the raw water hose pop off and a minor overheat the end of last year which cost me some new shutters. Compression test checked out and the mechanic said it did not hurt the motor. When I took the boat for a 5 min test run I noticed a bit of steam from the valve cover vent. Pulled both risers. Starboard side had the Sierria green gasket and the port had the graphite steal gasket. The starboard side was the side that leaked. Changed the oil 5 times and decided it was time for another trial. Put the oem steal graphite gaskets back in and replaced the starboard side manifold gasket (it did not really need to be replaced but I manifold off so I put a new gasket in). Risers and manifolds looked good.

I just finished wet testing the boat. It ran great. I noticed that the starboard riser is too hot to leave your hand on for longer than a second or 2. Port side was barely warm. The temperature will go up to 180 (I did not let it get any warmer) while running at low speed and drops to 150 when cruising. There is less than 25hrs on the impeller, which was replaced last year when the engine was completely rebuilt. I have run this boat a lot on the muffs while diagnosing the overheat issues.

To me this seems like an impeller issue, if there is an issue at all. Admittedly, I recall the boat was listing slightly to port during the wet test so perhaps this was directing more water to the port riser. I plan to check the water pump inlets and outlets and the thermostat.

Is there anything else I should check or am I wasting my time and should just replace the impeller? Perhaps I am being overly cautious as I am pretty sure the starboard riser has always run hot. This is probably why the gasket failed when the motor overheated although the oem gasket may have protected the port side.

 

[alldodge]

Re: Running hot at low speed

If we had a bit more info on what year, and type the engine was may possibably provide more spacific input. Given what you provided 180 degrees is to high, make sure your thermostat is 140 carb, or 160 efi. Check all hoses for restrictions and if the thermostat housing has the correct sleeve in it, that is if it uses one. Chck yourpower steering oil coller that it doesn't have pieces of the impeller in it. What gaskets were used on the risers.

How about the engine serial number to help us help you

 

[rock doc]

Re: Running hot at low speed

Sorry for the lack of motor info.
1991 4.3 2 barrel 175hp
alpha 1
21' all american larson with a small cuddy
2850 pounds dry

The thermostat appears to open at 160 and close at 140.

I put the oem gaskets in - open window on all 4 water journals. It is a closed loop riser that is blocked off so it is set up for raw water feed. Picture of the engine specifics below.

 

[rock doc]

Re: Running hot at low speed

A few pics of the starboard riser.

 

[rock doc]

Re: Running hot at low speed

The water intrusion at the riser/manifold joint due to the scorched gasket seems to be remedied with the new gasket.

 

[rock doc]

Re: Running hot at low speed

Now that you mention the power steering pump...it does have some chatter when you turn the steering wheel fast. Could this be a related issue?

 

[rock doc]

Re: Running hot at low speed

Here is a photo showing the riser setup.

 

[rock doc]

Re: Running hot at low speed

Although I did not run the boat very long after the raw water feed line from the drive fell off, is it possible that I damaged the belt driven circulating water pump mounted on the motor?

 

[alldodge]

Re: Running hot at low speed

A few pics of the starboard riser.
View attachment 204315View attachment 204316View attachment 204318

Looks like quite a bit of rust in the channels, try to verify there is no other scale build up or restriction. The gasket is the wrong type, it should seal off water from entering exhaust gases. See item 3

The water intrusion at the riser/manifold joint due to the scorched gasket seems to be remedied with the new gasket.

Hope this is what item 1 is above

The cooling system shown below identifies a sleeve used with your thermostat and it should be in place to help direct water.

Now that you mention the power steering pump...it does have some chatter when you turn the steering wheel fast. Could this be a related issue?

No this issue would not cause chatter with the power steerin system. I mentioned the power steering because of item 23 in the pic of the cooling system. If your impeller came apart some of the pieces may be caught in the cooler. Need to talke the cooling hoses off and see if there are any pieces found. Pieces in this area restrict water flow.

 

[rock doc]

Re: Running hot at low speed

I replaced the gasket in the picture with an OEM (pic below). The riser and manifold seemed to be unrestricted when I had it off the boat, but I understand your concern about the rust. They will need to be replaced soon - maybe this fall. Really appreciate your time to post all the schematics...the are very helpful. I will check the rest of the cooling system for restrictions and to see if the sleeve is in place.

 

[rock doc]

Re: Running hot at low speed

Checked the entire cooling system and no restrictions. Even pulled the v-belts and water pump/power steering and alternator all spin really nicely. No debris in power steering cooler or thermostat housing.

Turns out it may be a really simple fix. It had a 160F thermostat and should have a 143F. Installed a 140F and hopefully this will help the starboard riser run cooler.

 

[alldodge]

Re: Running hot at low speed

The lower TS should help, and hope it gets you going

 

[rock doc]

Re: Running hot at low speed

Thanks AllDodge. This site has been an amazing source of info. I have read a little more on this site and found another interesting bit of info to double check. Seems Bond-o and Don S have seen some issues with the thermostat housing before. There is a chance that I have the Bravo housing, which bypasses too much water for the size of my Alpha pump. I think I'll run it first with the 140F thermostat and see if this fixed the problem. I'm tempted to run a line between the block off outlets on the risers to balance out the flow/pressure (see pictures below). Has anyone tried running a line to connect these inlets before? I highlighted them with a red line.

 

[alldodge]

Re: Running hot at low speed

There is a chance that I have the Bravo housing, which bypasses too much water for the size of my Alpha pump. I think I'll run it first with the 140F thermostat and see if this fixed the problem. I'm tempted to run a line between the block off outlets on the risers to balance out the flow/pressure (see pictures below). Has anyone tried running a line to connect these inlets before?


View attachment 204548

The 140 degree TS should help, but looking at you TS housing pic I see your TS is upside down. The spring on the TS goes down according to the layout I'm looking at. The spring needs to face the water coming out of the block.

I have not heard of anyone running a line between them and don't think that would work and may also complacate things.

 

[rock doc]

Re: Running hot at low speed

I turned the TS housing over and partially removed the white plastic flow "diverter". The thermostat cannot be accessed from the top.

 

[Bondo]

Re: Running hot at low speed

Thanks AllDodge. This site has been an amazing source of info. I have read a little more on this site and found another interesting bit of info to double check. Seems Bond-o and Don S have seen some issues with the thermostat housing before. There is a chance that I have the Bravo housing, which bypasses too much water for the size of my Alpha pump. I think I'll run it first with the 140F thermostat and see if this fixed the problem. I'm tempted to run a line between the block off outlets on the risers to balance out the flow/pressure (see pictures below). Has anyone tried running a line to connect these inlets before? I highlighted them with a red line.


View attachment 204547View attachment 204548

Ayuh,.... I ain't sure What housin' you've got,...

Nothin' like those on my 4.3l, 'n Bobby's 350s he's throwin' together,.... All Alpha drives,..

Maybe ya oughta be browsin' the parts look-ups, or shop manuals to Id what you've got,...

The capped risers are no doubt not good,... Those aren't Inlets, they're Outlets,...
They keep the exhaust Wet, so's ya don't burn up the rubber parts,...

 

[rock doc]

Re: Running hot at low speed

Thanks bondo.

I'll pull the housing back off and see if there is a serial # on the underside. Very kind of them to stamp the serial number on the underside of the housing. I looked at MANY skematics and it could be a 860256A3 and or 860256A4. There is no apparent visual difference between these housing on the merc site or various other sites.

Judging by the numerous housing configs I'd hazard a guess that alpha and mercruiser had a lot of trouble with the engineering on the cooling. I read that they now have an updated housing that does not need the poppet balls but cannot find the service bulletin or part number.

Curious as to why are you concerned about using a capped close water riser (or maybe this is a warm manifold riser?) on a raw water feed setup? Why would this behave any different than one bunged flush with the outside of the riser housing?

 

[rock doc]

Re: Running hot at low speed

Water tested the boat yesterday. It ran flawlessly, but seemed to be a little too hot. 160-170F on the top on the block near thermostat housing. Starboard riser 140-160F, port 110-130F. Water line to the starboard side manifold is noticeably hotter - Port line was cold. This is a cold water setup.

I assume that the temperature is actually higher at the thermostat than what the IR gun indicates. Maybe 10-20F? The only thing left that I can think of is to pull the drive and check for a blockage.

 

[alldodge]

Re: Running hot at low speed

Sounds like a plan and with the setup you have I'm starting to wonder if the person before you change some things

 

[rock doc]

Re: Running hot at low speed

She is running great. Starboard riser temp is around 140F on the Starboard side and 100F on port side. Put 6hrs of running on the motor with no issues.