Mercury engines Temp question...
 

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

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.

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