Mercruiser new manifold getting hot??

[Andy456]

Hi people some input on this would be great and put my mind at ease. I have fully rebuilt mercruiser 5.7 done around 35hrs now. Was concerned with the old exhaust manifold and risers as they were the old ones and showing there age. Replaced them this evening and ran the boat and after a good run the manifold are to hot touch to the point I can’t hold my hand on them? Is this normal. The water pump was replaced the the same time the engine was rebuilt. Engine temp doesn’t move past 140 no mater what i do.

 

[alldodge]

Its a 5.7 but what vintage?

The mans not instantly burning you may be ok, did you use the correct gaskets between mans and elbows?

 

[Andy456]

Thanks for your reply. Yes I used the restricted gasket as mine has the hose onto the bottom of the manifold and the other hose that goes to the riser. Run fairly warm on normal speed but anything over 3000rpm they get real hot to the point you can just about touch them but not hold your hands on them.

 

[alldodge]

Its a 5.7 but what vintage?

As in what year

 

[Andy456]

The engine is a 2000 vortec motor with the old running gear from a early 260 engine

 

[Andy456]

Also running a early alpha gen 1 leg so the impeller is smaller in these drives to the newer gen 2 legs

 

[aerobat]

i have a 2006 5.0 mpi b3 and both manifolds are too hot leave a hand on it for sure . risers yes , but exhaust manifolds no . i think thats pretty normal .

 

[alldodge]

Being a previous 260 this would put your cooling system in the mid to late 80's. Probably have a cooling system like this



and should be using a gasket like this

 

[wingless]

The exhaust manifolds, risers and elbows on my Mercruiser 454 MAG MPI engines may be continuously hand held while operational.

Prior to my exhaust redesign, excessive temperature was indicative of corrosion failure. Now my exhausts always always look new, on the path for indefinite life...

 

[Andy456]

The picture is correct for my cooling system and yes I’m running the restricted gaskets in the manifolds. Maybe I’m just worrying about nothing?

 

[alldodge]

The picture is correct for my cooling system and yes I’m running the restricted gaskets in the manifolds. Maybe I’m just worrying about nothing?

Could be and is understandable
Could change the thermostat housing and remove the top hoses and run them a tad cooler

 

[rock doc]

Long shot...Did you ever burn up a set of exhaust flappers? If so there could be a blockage in your y-pipe.


Did you check for blockages in the cooling system? Maybe is is worth trying to back flush it to see if anything comes out.

 

[Andy456]

The flaps are all ok and are new I checked these when I replaced the manifolds. Is there away of testing the flow rate from the impeller? I heard you measure it in a bucket? Don’t want to pull the boat out the water drain the gear oil and split the drive to check the impeller if I can do a simple test in the water just by pulling the hose of a running it into a bucket them measure it??

 

[Andy456]

Any info on the bucket test

 

[alldodge]

Any info on the bucket test

I've heard many folks mention about how long it would take to fill a 5 gal bucket, but that IMO is just guessing. Boat does have to be in the water to test, not on a hose

I like installing clear hose between pump and thermostat housing to look for bubbles