how hot is too hot?

[muskyfins]

I have a 1993 stingray 606 zpx. 20 foot open bow with an older but impeccably maintained mercruiser 188/888. (5.0 ford not original to boat) I boat on the illinois chain o lakes where the river runs through several lakes so you can run wot through the lake but then have a bit of river (or channel) of no wake. At no wake speeds, my water temp stays right at 160 degrees, but when I bring her up to wot or even cruising speed (approx 3500 rpm), the temp climbs to as much as 200 degrees. After about 5 minutes I'm usually at the next channel and have to drop back to no wake. Within a few minutes of no wake, she goes back to 160. It seems to me that 200 degrees is hotter than normal. I haven't had a chance to run at spped much longer to see what would happen next. (but I will in the next couple of weeks) How hot is too hot?

 

[Don S]

Re: how hot is too hot?

Way too hot, you should have a 143? thermostat in it, which would mean you should never see over 160? or 165?.

200? is to hot for any engine in a boat.

When was the last time the impeller was replaced? The thermostat? Timing and advance timing checked? What is your WOT (wide open throttle) rpm? If it's too low, you are over-working the engine.

 

[muskyfins]

Re: how hot is too hot?

Greeeaaaat.

The impeller was replaced in 2009, but wasn't used 2010 or 2011. The thermostat was replaced this spring by the guy I bought the replacement engine from. (a 30 year certified mercruiser mechanic whom I trust)....(although I thought he said it was a 165 degree) I ran the engine on a stand before purchasing and never ran hot and after installation on muffs and never got hot. I know those are different than running with a load, but that seems to lead toward impeller. Engine runs so smoothly, I never gave timing a second thought and wot RPM is 4200.

I have lots of automotive experience (I know not the same as marine) and I have a very thorough technical background although I'm not a degreed engineer, but wouldn't you expect the forward momentum to overcome a weak impeller and then have a problem pumping water at low rpm's?

Also, I heard an "urban legend" about the impeller housing warping with age and allowing exhaust gasses into the cooling system when under pressure and not at idle due to the lower exhaust pressure. Any reality to this?

Thanks for all your help and to all those who offer help on Iboats. It has made my boating much more enjoyable and less expensive. (and most of the people here are better at diagnostics and trooubleshooting than most marinas around where I live)

 

[Tail_Gunner]

Re: how hot is too hot?

Looks like it is time for a new impeller. Don harps all the time about changing it reguraly once a year..He's right i caught one two yrs ago hard to believe but it happened. Now if your impeller is intact that does not mean you dont have impeller parts (fins) stuck in the cooling system some where from previous ownership.. they get stuck everywhere in the system and find the toughest spot ot find to get caught in.

Now i am being a bit smart a@@ here it maybe time to shake hands with your engine and learn some marine stuff..it's really...eye opening... check out the cooling system completely.. all of the wonderful nook's and cranny's and just like a engine bay the bilge has all kinds of new adventure's..scraped hands..wonderful combination's tool's to get at something and well see for yourself. Then a yrly inspection begin's to make sense. Ohh take a good look at what it takes to remove a bilge pump noitce how they neatly hide the wiring...Devise a plan now.

 

[ktbarrentine]

Re: how hot is too hot?

Pop the t-stat out and test it, too. It should be stamped with the temp rating. Get the right one for your motor.

 

[maproy99]

Re: how hot is too hot?

Going to say, I had a very similar problem. It was caused by a rusted water pump. Are you using a portable temperature checker or the temperature on the gauge on the boat. Wouldn't be the first gauge I have heard of that is off by more then a few degrees due to too much wiring in the boat- too much resistance. Or you could also check the temperature sender with a multimeter and make sure it has the right resistance for the temperature.