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-   -   Mercruiser Black Scorpion Temperature Range (http://www.wakeworld.com/forum/showthread.php?t=798867)

whodah 06-30-2013 5:23 PM

Mercruiser Black Scorpion Temperature Range

What is a good temperature range for a Mercruiser Black Scorpion 5.0 to be operating at? On a hot day (110 degrees out), cruising along at 25 MPH, is 180-190 on the warm side or is that acceptable? The middle of the gauge is at 160 and the upper limit on the gauge is 240, FWIW.


kronoss 06-30-2013 6:15 PM

I think 160 is optimal, but chevy blocks can run up to 200 no problem. 220-240 you will probably need a new headgasket.

Dmac420sj 06-30-2013 6:23 PM

Check your impeller

bstroop 06-30-2013 7:45 PM

Mine runs at 165ish all the time.

whodah 06-30-2013 7:53 PM

kronoss: thx, nice to know.

Dmac420sj: Roger that. Did that 2 years ago after having to be pulled to the dock due to a shredded impeller clear on the other side of the lake. Sigh. I was planning on it again after this season, but will look into it.

bstroop: Nice. On really hot days too, or is that pretty much irrelevant?

I broadened my search to just Mercruiser and came up w/ some more hits. From: http://www.thehulltruth.com/boating-...mperature.html I saw a post saying:

Raw water cooled engines should operate between 140 and 160 degrees. Fresh water engines should run at 170-210 degrees.
And this site: http://www.perfprotech.com/blog/arti...ouble-shooting stating

Most marine FWC thermostats open at 160F and will be fully open at approximately 180F. A new clean system under moderate load should operate at the lower end of this range and a dirty system under full load might operate in the upper range. Any temperature that reads outside of this range is abnormal and should be investigated.

boardman74 06-30-2013 8:11 PM

Yep most of the chevy blocks have a 160 degree. If your running that warm you have a problem. Air temp should not matter. You have an unlimited supply of 70-80 degree water no matter the air temp. Mine goes to 160 and sits there all day whether its 50 or 105.

nailem 07-01-2013 5:31 AM

mine runs right at 175 all the time under power and 160 at idle.

bstroop 07-01-2013 5:49 AM

Agree with whats said above. Air temp doesn't factor in.

04avyboarder 07-01-2013 7:28 AM

Mine has always run @ 175

whodah 07-01-2013 9:12 AM

Bummer. I don't like reading that, but I appreciate the info all, ty. I'll start checking it out. Maybe I'll get lucky and a piece of the previously shredded impeller is still in there or something. Of course the family wants to take it out on the 4th. I'm going to preemptively order an impeller and thermostat rush delivery now. Maybe a water pump too, depending on price. I'll try to get in there tonight, but it is going to be 112-115 degrees here today depending on which weather station you listen to, so we'll see.

Dmac420sj 07-01-2013 9:39 AM

Impeller 20 min get sweaty dude!

whodah 07-01-2013 10:38 AM


Originally Posted by Dmac420sj (Post 1831003)
Impeller 20 min get sweaty dude!

translation: man up!

Ha ha! Good point, you've convinced me.

I'm searching and learning, and normally I wouldn't ask this without researching more... But since time is of the essence to try to get the out-of-town family out this 4th: would a seasoned member here kindly help me find the part number for the impeller and thermostat based on my engine so I can order it today?


Thanks, guys!

whodah 07-01-2013 10:42 AM

Oops - meant to also post: I'm thinking the part numbers are:

impeller: 47-862232A2

thermostat: 807252T 2

And also: if someone would like to kindly recommend a sponsor from this site or a favorite vendor, I'll give them the sale. :)

Dmac420sj 07-01-2013 10:45 AM

What kinda boat?

whodah 07-01-2013 10:52 AM

It is a 2007 Sanger V215.




Dmac420sj 07-01-2013 11:17 AM

Big sang dog!

whodah 07-01-2013 11:21 AM


I was really surprised, but I was able to find a local vendor with them in stock!! I'm headed out there for lunch to pick them up.

Dmac420sj 07-01-2013 11:38 AM

Where you at

whodah 07-01-2013 11:55 AM

Clovis, a suburb of Fresno, California.

whodah 07-01-2013 10:43 PM

Bummer, impeller looks good. As soon as I had the water pump off, I could see through the inlet/outlet tips of the impeller that looked good and sighed. What do you guys think?



I've been reading about back flushing due to my previously shredded impeller. I did not do the replacement then, but I was around. I know he popped off the hose and cleared out debris from that first filter-type area post water pump. (please forgive my ignorance on the part names) I pulled the hose off tonight, and it looked clear. 1 small piece of grass that I pulled out:


I then backflushed that hose w/ a garden hose. Then I went to the other side of that fitting, pulled that hose off both ends and backflushed that. I did not pull off the "T" side of that fitting w/ the smaller hose. I.e. I did not pull off nor back flush the bronze colored piece part headed downward in this photo:


I kept following the main water hose to this contraption and back flushed that:


And... that's where I'm at, still disassembled. I'm thinking I'll swap out the impeller with the new one I got. The old one is 1.5 years old and only has maybe 40 hours on it tops. (probably more like 20)

Any advice is appreciated. As mentioned earlier, I've been reading about back flushing, but can't really find any info on where to do it. My next thought was that brass fitting hose mentioned above.

And again - thanks, all!

04avyboarder 07-02-2013 4:55 AM

This link may help locate any debris http://www.centurioncrew.com/index.p...r/?hl=impeller

whodah 07-02-2013 4:38 PM

Popped in the new impeller, fired it up, water coming out of the back, still engine temperature gauge still reading ~180. Actually like 178, the needle is JUST before the 20 degree increment mark indicating 180 degrees. Called someone out that had helped me before, and he hooked up an engine diagnostic tool. After fiddling w/ the fake-a-lake a bit, everything looked nifty. Including the temperature at... 158 degrees! We watched it for several minutes. Revved it up, ran it for several minutes. We watched the temperature go up and down ~5 degrees on the gauge, and up and down ~4 degrees on the Mercury Engine Diagnostic Tool. Highest we saw on the Diagnostic Tool was 159. Lowest was 155.


Well, now I know to offset the temperature by approximately -20 degrees!

I'm wondering if I should pursue fixing that, or just letting it be knowing the offset... Opinions appreciated.

Thanks, all.

whodah 07-08-2013 12:03 PM

Final thoughts: the engine performed well at the lake. Put several hours on the engine with the new impeller. Temperature stayed steady at ~173 degrees according to my thermometer gauge, which would actually be ~153-156 degrees based on previous tests if I had a computer hooked up to the engine. It was cooler w/ the new impeller which was reading ~178 w/ the old impeller on the gauge (~159 w/ a computer hooked up).

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