'87 Yamaha 150 Running Hot at Idle
 

Lovin' this motor, but it's run hot twice now while trolling at idle speed. Before I picked it up, it got a new water pump and T Stats, so scratchin' my Levis over what's causing this.

The real puzzler is it trolled for hours one day and did not overheat.

Any ideas?

My 150 merc does the same thing sometimes she's good and sometimes she runs hot, what so you expect from a women lol With the merc you also have a poppet valve that would cause overheating Don't know if yamahas have them

check the PRV(poppet valve) sounds like its sticking

My question is always, have you verified that it is actually overheating? Thought those engines were pretty basic with not much of anything to worry about. One thing I would look at is if air is getting in the cooling system. I know failing head gaskets can push air in at slow speeds and cause overheating, but at higher rpm's the water flow is enough to overcome the air getting in.

Ferm, when I shut it down and take the cover off, the top of the heads where the T stats are is VERY hot..leave the cover off for 15 or so minutes, try the ignition til the horn doesn't sound and she'll run great.

Where is it?...I'll have to find it...can I unstick this one, or should I get a new one?...:head:

between the heads on teh exhuast plate, just take it aart, make sure nothing is wedged in there, clean it up and put it back in, you may need a new gasket

could a base gasket also allow air into cooling system?

Will do, Spare...appreciate it...:sun::sun: