Is my 4 cyl 50 hp Merc running too hot???

[Steve2ManyBoats]

I have a late 80's Merc 4 cyl 50 hp on my bay skiff. Always loved these motors and have had a few over the years. They run very, very smoothly and tend to last forever...or until the water jackets corrode to powder.

My current 50 Merc is running flawlessly, but I noticed today that the water from the tell tale is quite hot. The stream from the tell tale is very strong, but hot. I put my IR gun on the motor and this is what I found:

Temp of side exhaust water jacket - 110 deg.
Temp of back of block by spark plugs - 150 deg.
Temp of water from tell tale 130 deg.

Bay water temp is 78 deg.

The motor seems to be running hotter than other 4 cyl Merc 50's that I've owned. I haven't installed a water pressure gauge on the motor - I usually don't on small motors.

Is my motor running too hot or is it OK?

Advice appreciated...Steve2ManyBoats.

[Steve2ManyBoats]

Anyone?

[Slimm]

I think thermostats are about 143-145 degrees. I wouldn't think those temperatures were bad.

Slimm

[Steve2ManyBoats]

But 4 cylinder 50 Mercs don't have thermostats. That's my concern. The readings I got seem a little hot for a motor with no thermostats.

Experiences and advice appreciated.

Thanks...Steve2ManyBoats.

[Steve2ManyBoats]

Any thoughts on whether these temps are OK for an 80s 4 cylinder 50 Merc considering it has no thermostat:

Surface temp of side exhaust water jacket - 110 deg.
Surface temp of water jacket on back of block by spark plugs - 150 deg.
Temp of water from tell tale 130 deg.

Appreciate any advice/experiences.

Thanks...Steve2ManyBoats

[Slimm]

As I stated previously, I think those temperatures are fine. Is the engine giving you problems that you think are related to temperature? Have you tested the other engines you had with the infrared thermometer? How did you come to the conclusion that this engine is running hotter than the previously owned engines?

Slimm

[Steve2ManyBoats]

PROBLEM SOLVED - Turned out the impeller was weak. Popped in a new impeller and the temps went down a lot. The old one was only a year old, but had taken a set. Rear water jacket water temp went down 20 degrees. However, the tell tale stream didn't change with the new impeller even though the new impeller clearly is delivering more volume. That's what threw me - stream seemed fine but the motor was not getting enough water volume.

I didn't have an IR gun the last time I owned a 50 Merc. But that motor never ran hot. The tell tale stream was only warm to the touch and you could hold you hand on the rear water jacket as long as you wanted. On this motor, before the new impeller, you could barely hold you hand in the tell tale stream, even though it was strong, and you could only touch the rear water jacket for a few seconds.

Since this motor seems to need a strong impeller, it's probably going to get a water pressure gauge like all my V6s do.

Steve2ManyBoats

[Slimm]

Glad you got it figured out. Sorry I couldn't be of any more assistance.

Slimm

[W2F a V-King]

Maybe Mercury changed the plumbing location between different years for the tell tale? My 1971 9.8 always had hot steamy tell tale, but none of my many V6 Merc's ever did..warm, but not hot.

Yes, those old 4 cylinder Merc's are smooth as sewing machines.

James