Temperature of exhaust manifold?

[High Bidder]

I finally got my boat out for a test run.(5.0 OMC IO) I installed a new lower unit water pump and the engine temp stays at 160 degrees. However, the exhaust manifolds seem to run at different temperatures. On the port side I can hold my hand on the manifold(probably about 120*) the Starboard side is a little hotter and I can only hold my hand on it for about 10 seconds. How hot do these things get? When I replaced the heads this spring I flushed the manifolds with muratic acid to clean the loose rust from them and water flowed freely through them. The riser seems hotter than the manifold. Should I be looking at the water pump system or the manifold system?

High Bidder

[borderline 350]

Dear HB,

Be sure and check the water exit hole inside the risers on the outlet side. The hot side may have partial blockage. OR you may have partial blockage inside the hose or thermostat distribution elbow to the "hot side" Either way at 1500 RPM (constant) both elbows should cool down and should feel the same (in neutral, no load on engine). If you have access to a hand held laser temp. gun, they shouldn't be over 160 F. or whatever the engine temp. is. Did you acid clean the inside of the risers when you did the manifolds? Good job using the muratic acid!! Let us know what happens!

Respectfully submitted,

............Jet Boat Bill

[L&M]

Also depending on year. Check the two nylon check balls & springs on the thermostat housing that go to the elbows.

[High Bidder]

Okay, I removed the riser and first ran 3/16" flex rods in all the water ways. When I hit it with 3500 PSI pressure a lot of rust particles and a few chunks came out. I then applied another acid bath for 10 minutes and rinsed again. I seem to get better flow through it now. If I test run the engine on ear muffs will that give me a true flow rate or will the water pressure from the hose provide more flow than the impeller pump normally does? Is trying to use this riser a bad idea? Should I just buy a new one?

I had cleaned both the manifolds and risers with muratic acid when I pulled the engine to replace the oil pan and heads.

High Bidder

[borderline 350]

Dear HB,

As long as the manifolds have not been run in Salt Water, you should be OK with the used one if you get all the passages clear. Try putting the boat in the water and running it at 1500 RPM in neutral. Both manifold risers should be barely warm to the touch, but not too hot to touch! If the I/O pump impeller is working properly, all should be OK. It wouldn't hurt to pull the engine water pump and check for blockages and excessive rust scale...if it continues to run hot. Fresh Water risers will go 6000 hours, then usually burn THRU in the elbow. Salt water elbows will only last only a couple years and then RUST THRU!

Respectfully submitted.....Jet Boat Bill

P.S. Be sure and use a marine thermostat in order to get proper waterflow!

[High Bidder]

Well, I think the problem is solved. I ran the engine as suggested and tested it with a borrowed laser temp gun. The manifolds and risers were 143 degrees even after running the engine at 3500 RPMs under load for 15 minutes(after a 15 minute warm up) The end of the manifold fartherest from the water inlet was 10 degrees warmer than the inlet end which I assume would be normal. Both risers were the same temperature on all sides and tops. Also much to my delight, there was not a drop of water in the bilge since I had removed and resealed my gimbel housing last winter. Thanks for the tips and information. Now as soon as the salmon hit Mexico Bay I'll start fishing again.

High Bidder