2452 5.7 New exhaust manifold temp?-gctid815703

[jameslee97206]

Hi, I bought this boat about a month and a half ago. On the muffs it ran around 120 degrees before I bought it. Temp gauge is actually not accurate so I found. First trip out it stumbles an dies, seems to have overheated, let it cool down, it starts, I motor back to the dock and trailer it home. Replace exhaust flappers and impeller, pull drive to check for flapper remnants in exhaust bellow. Fire it up on muffs, runs great. With an IR temp gun, starboard manifold is at 110 ish, thermostat housing about 145 to 150 then it drops. Seems good, shoot port manifold its at 215. I had the risers off when I changed the flappers, looked rusty and a water jacket was partially clogged. New manifolds and risers. starboard manifold is at 110 ish and port started climbing, I shut it down at 175. It's a partial closed cooling with raw water cooling manifolds. 5.7 Mercruiser. I pulled the drains on both and the port side had more water than the starboard side come out. Was thinking a clogged heat exchanger, but with the manifold draining water, am I over thinking this? I read a bit and understand they wont be the same temp, garden hose might not have enough pressure . Any thoughts? Thanks in advance PS, boat has seen mostly salt water use

[Chief_Alen]

Bravo drive ?

[jameslee97206]

"Chief Alen" post=815716 wrote:
Bravo drive ?

Alpha 1 gen II

[Chief_Alen]

So you changed out the impeller in the drive, complete new housing ?

[builderdude]

You say you've replaced the exhaust manifolds and spacers (risers) What about the exhaust elbows, have they been replaced also?

[jameslee97206]

I replaced the impeller in the drive, not the housing though, I just cleaned it up. I see the elbows are often called risers? I changed the elbows with the manifolds. There was no spacers between them. I guess I'm wondering if I'm wasting my time trailering it to the river and checking temps while in the water. Should the manifold get that hot while on a hose?

[Chief_Alen]

You should be able to leave your hand on it.

New impeller housing complete kit I always do, also the shift shaft bushing.

Take the incoming raw water hose off the first stop say the t-stat housing place in a bucket, with the drive submerged start the engine for 15 seconds quick shut off the engine, how much water is in the bucket ?

[jameslee97206]

I'm pretty sure the impeller is working as there is plenty of water coming out of the exhaust bellow. The starboard manifold is running around 110. Thinking it might be a clog in the heat exchanger or the hose is simply not putting out enough volume to cool both manifolds. Any thought?

"Chief Alen" post=815775 wrote:
You should be able to leave your hand on it.

New impeller housing complete kit I always do, also the shift shaft bushing.

Take the incoming raw water hose off the first stop say the t-stat housing place in a bucket, with the drive submerged start the engine for 15 seconds quick shut off the engine, how much water is in the bucket ?

[builderdude]

Bump rpm up to 1000-1200 and see if that side cools down. One side can run a bit warmer than the other while the engine is at idle rpm. A touch more rpm equals a touch more water flow from the impeller.

Chief wants you to measure the flow volume from the impeller, I agree. It could be pumping but not pumping enough. You could also pull the end caps from the exchanger to check for blockage and look for possible blockage in the hose leading to the warmer exhaust components.

[bhawes]

That port side at over 200 degrees is running way to hot. That will melt the flappers and start doing engine damage in short order. I'd suggest getting a hold of a water circulation drawing for that engine and checking everything serving the port side for a blockage, starting at the heat exchanger. You can put 14-16 gauge copper wire into the small ports in the ends of the exchanger to check for any blockages there. Remove the rubber hose from the bottom of the heat exchanger, and the exhaust manifold and check for any obstacles. Is there any chance that you somehow installed the wrong gasket at the base of the elbow? They often come with the gasket for both raw water and closed cooling and they are not the same. Another simple test is to remove the blue plastic plug on the bottom of the port manifold. When the engine is started on muffs, there should be a pretty good stream of water coming out of the threaded hole that you removed the plug from. If there's good flow there, you know that the problem is from there back. If there is little or no flow, the problem lies further forward. Turn the motor off and begin your search. Good luck.

[jameslee97206]

I put it in the water tonight, ran it at the dock about 1100 rpm until the thermostat housing was at 145, both elbows were then at about 90 degrees each. I left and ran it down the river at around 3100 rpm, 25 mph for about 20 minutes, checked temps again. Thermostat housing 155 and both elbows at 110 and luke warm to the touch. Looks like my hose didn't have enough pressure. I really appreciate all the help and good advice. I was loosing sleep over this. Now a few more fixes and it looks like I have a good boat!

[Chief_Alen]

Volume not pressure.

Anyway enjoy.

On a hose you should never exceed 1200 rpm.