Mercury engines Temp question...

[jjjtronics]

One of my co-workers have a pair of 150 Merc`s, two strokes, and he is concerned with this;
Both motors run at 3/4 on the temp gauge when at 2k rpm, at 4k rpm, the gauges drop to 1/4 temp. Engines run fine, he is concerned, is this common or normal. He trolls a lot, so he have a good reason to be woried.
Anticipated thanks for any advise.
JT

[THEFERMANATOR]

Normal operation. It wouldn't hurt to replace poppit valves in the adapter, but what your describing is normal for just about any 2 stroke. A 2 stroke looper engine needs alot of heat at idle to burn the fuel without loading up the plugs, but under a load they need to run cool to keep from sticking a piston. It isn't uncommon for a 2 stroke to run 160-170below 2000 RPM's, and then drop down to 100-130 under load. They have a spring loaded valve of some kind to allow the thermostats to be bypassed once a certain amount of water pressure is reached which there fore drops the engine temps way down. Once the water pressure comes back down the T-stats go back to working again and temps go up.

[jjjtronics]

Thanks Thef...
I will pass your knowledge to my friend.
That is very logical and well explained.
I rely on the cooling water external-stream for my Yamaha eng temp., I trashed the gauges which were bad. My 2S also acts exactly as you described, warm at idle, cold at high rpm.
THANKS MAN !!!
JT