Manifold Temperature

[abraxus]

I was talking to my mechanic today and he mentioned that whilst servicing my engine he noticed that the manifolds were getting a little hotter than usual.

He said he would check this out further but mentioned a couple of spring loaded ball type valves by the thermostat that were getting stuck which may be causing the higher temps, so he cleaned these up, but said that he'd noticed in lot of engines he'd seen, these balls had been removed altogether.

He suggested that maybe the fact that I am river based so subject to constant slow speed cruisng may a factor and is going to check out whether removing these balls is advisable or would help.

The engine is a Merc 5.7 raw water (fresh not salt) cooled. Hot water is also plumbed from the engine through the calorifier.

My questions are, does this sound reasonable? Any suggestions? And would castrating my engine be a possible solution or cause more harm than good?

 

[stelican]

If the engine runs cold there is a chance of the autochoke partially operating this giving a richer mixture and at low speed these fumes may well find their way into the cockpit . the conseqences could be fatal. I have known this to happen

 

[spannerman]

Mercruiser have done away with these plastic balls in the outlets to the risers some time ago, as they caused more problems than they were worth.The balls are in the hoses which only cool the risers so won't affect manifold temps.
Does your mechanic mean that the risers are getting too warm or the manifold below it, as both can rust internally and restrict water flow, though not neccessarily at the same time, although its advisable to change the risers if you change the manifolds, but if its just the risers you can often get away with changing just those.
Also how long since the water pump impellor was changed.
Could also be something as simple as the thermostat, as your motor has a split cooling system, with the hot water from the block going via the stat to the bottom of the manifolds and then exiting up through the riser, (whats the temp on the clock showing) if the stat is opening late then the manifolds being the last in the line will get hotter. Whereas the risers should have a constant feed of cooling water which bypasses the stat, if they have a good supply and are still hot then they are blocked.

 

[abraxus]

Thanks chaps.

I was aware that they'd done away with the balls, but according to their service bulletin that was in conjunction with a new internal design, so there are two types of housing, one with balls and the new one without. The bulletin says not to put the newer one on mine as the newer internals with a different sized bypass hole designed for higher seawater pump output of newer models. However it doesn't state whether I can remove the balls from mine.

He actually said manifolds, so I assume he means these, and last time I checked, riser temp seemed ok. Water pump impeller would have been changed recently at service.

Didn't see temp on clock as I wasn't with him at time, but last few times I ran the boat it was running at around 180 if I remember correctly.