What brand of manifold is being used for replacements?
Sierra and Recmar, both last few trips, rest of the boat is with Recmar
Is the cyl head flat & level where the manifold mounts?
Yes, did not test it with laser on the bench but with light and straight ( can not figure out, how this is called in English) tool it was perfect
How tight are the bolts for the manifold being torqued?
We use torque wrench, should be as required
I had a bad over heat once on my engine many years ago and even with the manifolds getting as hot as 375*F on the outside (IR temp gun) they did not crack, took them off tested with Acetone & no leaks, used for another 4 years no problems….these were the OEM OMC batwings V6 exhaust. Something is very odd there!
I would lay a mechanics straightedge across the exhaust ports to make sure all are flat & level. Same with manifold before installing. Also was equal water flow out of the stat housing to each manifold verified?
We swapped thermostat housing between engines, now differences noticed. Also measured with Flir IR gun, all 4 manifolds are +- 5c difference on idle and on full speed, all pipes are equal on temp between engines, water coming out from the side of the boat is on idle 28c on both engines. Can not find any difference on temp or water flow - physically checked all pipes, restrainer and verified that after opening the water, it was flowing freely in.
If not one side could be getting very little water. Manifold & elbow temps should be checked with an IR temp gun & compared side to side, both during warm up, idle and after coming off plane. If there are big temp differences then you have to find out why….usually one side is slightly higher but not a huge difference….
Like I said - no temp differences found on idle or with 3800 rpm driving. Elbows are always cold, so there is enough water, all 4 manifolds are hot and not really comfortable to touch with the hand, but not burning hot.
