Hey guys got a question on were to start on this. I am in a 1986 Nova 2 with twin 260 mercruisers and alpha ones. It does have thru hull exhaust and all gauges seems to be accurate oil pressure,temperatures etc etc. Well here is my deal if I lay into both engines after getting onto plane and start trimming and leave it on wide open throttle for a short time (less than a minute it seems) the starboard engine starts getting hot quickly it seems soon as I see it get over the 180 mark I let off and bring it back to around 3,400 rpms or less and cruise. But anything over 4k for a very short time it gets hot/warm. Port side engine never moves off of 160 doesn't matter if I am in the wake zones for a period of time or out running it remains the same. It is not a closed cooling system either. According to previous owner in Michigan it had new impellers last September and was put up for the winter. Then I bought it and brought back to Tennessee. Note I also always run my blower while going down the lake or at idel. Any help on this would be great thank you!!!

I'M NOT AN EXPERT but I have heard that if the engines are not in sync one will run a little warmer than the other -- I don't know if that is a urban legend or not so don't take this as gospel

3pointstar

I don't no if you have pulled any of the hoses yet to see if you have any clogs sometimes it does not take much. The first hose I would pull is the hose from the transom going to your pump, at the transom you have a plastic tube that can get clogged also pull your plugs on the bottom of the block they will hold some sand and stuff.

Good luck

160°F is still a little high for what most 5.7/260's run for temp. Not that it's dangerous, but it's a little high for normal. Are you sure Gauges are reading right ? Alot of marine gauges are cheap and don't. A lot of Gauges are switched without correct senders being installed.

These should have 140°F t-stats in them.

Being that your boat is old, some water passages could be clogging from rust/sand/etc. I'd take off t-stat housing and hoses. Take a look at those passages and install new 140°F Merc t-stats and Merc's t-stat housing gaskets. It's possible more water is going to exhaust manifolds vs prioritized to engine.

Pull those hoses off of exhaust manifolds and see if those passages are caked up too.

If all is good, work back towards transom and then nipple hose connects to at transom inside boat and then rubber hose outside boat from transom to drive.

Yesterday after taking my alternators off my boat I reached my hand back and drained one of the manifolds on the engine that likes to get a little warm and got a puddle of sandy soot looking stuff then water...so I gonna assume its blocking some cooling ports throughout..... What's the best way to flush a engine?

You should have two drains in the bottom of the block left side and right sand will get stuck down there, if water does not come out use a small screw driver and unplug it water should come out. Also check your water hose coming in from your transom that plastic piece collects junk. Hope you find you problem