How Hot Is Too Hot

[biloxiriver]

I have a friend who has a 165 mercruiser on a 20' wellcraft V20 steplift cuddy, the engine is the 250 6 cyl GM (a great engine incidentally). The boat is a 1973 model. It seems to run in the 190 - 200 deg range on the gauge, but we can touch the manifold which is too hot to maintain contact very long, but it does not burn/blister the skin. Our conflict is that local mechanics tell us that this engine should run in the 140 f. area (it has a new 140 deg thermo in it). Any thoughts out there??

 

[Ralph 123]

Re: How Hot Is Too Hot

WHat they are telling you is right. I run 350s and run in that range and can keep my hands on the risers without a problem. <br /><br />Check this out, it may help and probably explains yor problem:<br /><br /> Mercruiser Exhaust Tips

 

[crazy charlie]

Re: How Hot Is Too Hot

If the motor if raw water cooled then the 143 temp is correct.a fresh water cooled engine can run at the temps that you described and be fine. Charlie

 

[chris in va]

Re: How Hot Is Too Hot

Um, er...the GM 250 is NOT a great engine. I had one in my 77 Nova, and they are notorious for blowing the #1 cylinder rings due to faulty cylinder cooling jackets (doesn't go all the way around the cylinder). Right around the 90k mile mark they start using oil at insane levels, fouling the plug every 2 days. <br /><br />This of course is the experience with it in a car, maybe they fixed the problem on the marine model.

 

[biloxiriver]

Re: How Hot Is Too Hot

Thanks guys. Good info and kinda what I expected. Incidentally, Chris in va, I did not mean to imply that all GM 250s are great engines, just this one; it is the only one I have experience with and it runs great and is very efficient. But quite possibly it has to do with the marine application element. Beats me.

 

[magster65]

Re: How Hot Is Too Hot

It's only in salt water that is the concern. Hot salt water will eat away at cast iron really quickly.

 

[Ralph 123]

Re: How Hot Is Too Hot

Salt water eats everything! <br /><br />Remember that movie with James Cann where the aliens would melt in salt water - it was like acid to them? Well that happens to everything in the ocean it just takes a little longer sometimes

 

[flashback]

Re: How Hot Is Too Hot

I have a 350 merc and i can lay hands on the manifolds but don't try it on the valve covers! it hurts! goood luck