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Old 09-25-2020, 02:54 PM   #1
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Default Starboard manifold cooking

2002-5.0 MPI.
Boat runs about 185 degrees on plane, seems okay but also seems a bit warm, and sometimes it feels heat soaked even though temp guage says its fine.

I bought a IR gun and the starboard manifold reads around 175-180 degrees back to front.
Except at the front of the motor, it runs between 220-240 degrees.
That is the very front #1 cylinder only.

The port side 155-160 manifold and riser is about 160 degrees.

What could be causing the front of the starboard manifold to be boiling hot like that???.
New impeller, new thermostat.
Not sure where to start.
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Old 09-25-2020, 05:24 PM   #2
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When was the last time the manifold and risers were inspected or replaced? Sounds like a clog.
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Old 09-25-2020, 05:26 PM   #3
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I just replaced the other manifold and it was in very good shape.
No rust or blocked ports in riser or elbow.
Wondering if its a water pump issue, but no idea right now.
Thanks.
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Old 09-25-2020, 09:35 PM   #4
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Those temperatures are too high. Did this all start after doing some maintenance, or have your temps been like this since you got the boat?
Sounds like a water flow problem. Should be easy enough to figure out.
New impeller, is there a chance that the water tube didn't align properly when you put the lower unit back on?
Is it a 160 degree thermostat? Check balls look good on the thermostat housing? Plastic thermostat housing installed correctly?
If those are all OK I would suspect blockage somewhere. Disconnect the water inlet hose and do a flow check as described in manual #24. You want to ensure the impeller is giving you sufficient water volume.
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Old 09-25-2020, 10:59 PM   #5
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If the exhaust manifolds are not closed cooled they are way to hot. Open cooled manifolds should be around 120*F.
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Old 09-25-2020, 11:18 PM   #6
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The manifolds are water cooled, not closed system.
Just wondering where to start, before tearing apart my manifold.
I will order a new water pump and start there I guess.
Thanks for your help just the same.
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Old 09-26-2020, 02:28 AM   #7
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Quote:
Originally Posted by jrsick View Post
Those temperatures are too high. Did this all start after doing some maintenance, or have your temps been like this since you got the boat?
Sounds like a water flow problem. Should be easy enough to figure out.
New impeller, is there a chance that the water tube didn't align properly when you put the lower unit back on?
Is it a 160 degree thermostat? Check balls look good on the thermostat housing? Plastic thermostat housing installed correctly?
If those are all OK I would suspect blockage somewhere. Disconnect the water inlet hose and do a flow check as described in manual #24. You want to ensure the impeller is giving you sufficient water volume.
New thermostat, new implore, but not sure about the guy who installed the new impellor.
Will check for water flow etc.
Thanks.
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Old 09-26-2020, 11:17 AM   #8
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What’s the temperature of the water entering the manifolds? I would do the flow test per the Mercruiser manual to verify the raw water pumps output is correct.
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Old 09-26-2020, 01:12 PM   #9
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When I did a flow check, much more water pumped through the inlet hose than I was expecting. Get a big bucket and don't be surprised if you get an impeller fin.
If poor flow then I'd call the guy that put in the new impeller and ask if he's sure he did it right. If flow is good then continue to move up the line, you'll find the problem.
Engine driven water pump failure is a low probability. How many times have you heard of a water pump failing to flow water? Bearing fail, seals fail, but the connection between the pulley and fins rarely fails. The water pump could have problems if it wasn't winterized properly, but I think you would have heard noises or had pulley shake. If all else fails you could take the water pump off for inspection, but I wouldn't replace it without reason.
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Old 09-26-2020, 02:11 PM   #10
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The water entering the manifolds when tested was 175-180 degrees at the thermostate I believe.
The boat had just came off plane and was cooling down.

The water must not be getting to the front part of the starboard manifold cause it was reading 220-245 range.
The back 3 ports on the manifold were reading 175-180 range.

Blockage or not enough flow seems logical.
Going to take out on the lake Monday before end of season, see what I can find.
Thanks guys 240 range scares me a bit.
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Old 09-26-2020, 06:00 PM   #11
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175-180* is to hot as the thermostat housing mixes cool water with the water leaving the engine. What outdrive do you have? If a Bravo you may have Bravoities which is a know issue with the water hose getting clogged at the transom assembly due to marine growth on the inserts that secure the hose.
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Old 09-27-2020, 12:54 PM   #12
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Quote:
Originally Posted by mmwjr View Post
175-180* is to hot as the thermostat housing mixes cool water with the water leaving the engine. What outdrive do you have? If a Bravo you may have Bravoities which is a know issue with the water hose getting clogged at the transom assembly due to marine growth on the inserts that secure the hose.
Boat is fresh water, clear lakes.
Really is no marine growth on bottom of boat, or anywhere else.

I think I might have figured it out.
I switched the port manifold and installed non restrictive gaskets on riser and manifold.
It runs at 160 degrees.

I have not done the starboard manifold yet, but I think it might have a restrictor gasket in there somewhere.
Would that not effect the flow.???

I know the bravo flows way more water than a Alpha, and I dont think it uses a restrictor gasket.
Thats my thought.

The manifold from the port side was in great shape, so makes me thing it was swapped not long ago, and they might have used the restrictor gasket.
I will find out next week when I pull it i guess.
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Old 09-27-2020, 02:53 PM   #13
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Exhaust manifolds should only be around 120*F, you’re still to hot IMO.
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Old 09-27-2020, 04:15 PM   #14
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Was there any work done on your exhaust or cooling system right before you noticed the high temperatures?
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Old 09-27-2020, 10:27 PM   #15
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Quote:
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Was there any work done on your exhaust or cooling system right before you noticed the high temperatures?
The motor seemed to get heat soaked after a good run on plane.
Thats why I bought a IR gun to verify IO had a problem.

I just bought the boat so no idea what maintenance was done.
I have done plugs, thermostat, wires,Port manifold replaced etc.(Impellor was changed but temperatures did not change, old impellor was in good condition.

Temperatures where like this when i bought the boat in June.
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Old 09-27-2020, 10:28 PM   #16
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Quote:
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Exhaust manifolds should only be around 120*F, you’re still to hot IMO.
Press water cooled, 160 degree thermostat (New).
Maybe the manifold that is running really hot is effecting the other temperature a bit???.
I will replace starboard manifold and verify that it has or does not have a restrictor gasket on the manifold/ riser.
Thanks
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Old 09-27-2020, 11:09 PM   #17
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My guess is the reason that your port manifold looks good is because the previous owner replaced it chasing this problem.
Did you have a chance to do a flow test?
Are you sure your thermostat is 160 degree?
I don't think replacing the manifold will help, you need to figure out why the water temp exiting the thermostat housing is high.
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Old 09-27-2020, 11:55 PM   #18
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Quote:
Originally Posted by Mr Hemi View Post
Press water cooled, 160 degree thermostat (New).
Maybe the manifold that is running really hot is effecting the other temperature a bit???.
I will replace starboard manifold and verify that it has or does not have a restrictor gasket on the manifold/ riser.
Thanks
The engine temperature should be at whatever rating the thermostat is, in your case 160* however once the water leaves the engine it gets mixed with some cold water in the thermostat housing which then is plumbed to the exhaust manifolds and is typically around 120*.
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