Temp heats up as RPM increases
 

My temp gauge normally reads 160*-175* when I cruise 3200 rpm or less.
The past couple weekends I`ve noticed that if I run 3500-4000 rpm or more, the temp creeps up to 200* or so within a minute or two.
If I hit WOT, the temp goes from 175* to 210*+ within seconds. If I hold it wide open, the temp will hit 230*+ within a minute. If I slow down, the temp slowly decreases back to normal.
I replaced the thermostat (140*), no difference.
I am running a water pump cross-over also.
I`m not sure that the engine is actually getting hot. It doesn`t really feel much hotter than normal while it reads hot.
Any suggestions?????????

Donman, I had kind of the same problem as you. I had brand new water temp gauges that I had bought from Gaffrig. I even bought the sending units with the gauges. One is accurate and the other is showing that I am getting too hot, but touching the engines during operation they feel fine to the touch, however engines can get REAL EXPENSIVE in a hurry when they melt down so we took the engine hatch off and used a point and shoot laser temperature reading gun. Just point and squeeze the trigger and where ever the little red laser dot is at that is where it takes a an immediate temp reading that shows up in a small digital window. We took readings from ALL OVER the engine----thermostat housing, water lines, oil lines, fuel lines, oil coolers, power steering cooler, block, intake manifold, primary tubes on the headers, heads, tailpipes, etc.

It takes ALL the pain in the butt guess work out of trying to figure out what is going on. The tool may not be the answer to your problem, but it might help you solve it much sooner. Turns out that the temps showing up on the gauge and what we were getting from the temp gun were two different readings---the engine was running NORMAL water temps. It was the new gauge that was NOT working correctly! We removed the engine hatch and took the readings under normal boating/operating proceedures (on plane and at various RPM ranges)----as I drove my cousin took the temp readings.

You might try running your engine without a thermostat and see what happens, but I don't really know if that is good/safe advice. Perhaps someone else can chime in here and help you out. Best wishes :)

TOO LEAN?
I have been toying with the carb jets lately. Could it be a LEAN condition?
I`ve got 87 in the back (800 mech sec Holley). Plug reading does not indicate too lean but....................?

Budah might be able to help you out on this---sit tight and he'll show up soon enough. :)

Just remembered...........
It did this once before (before I leaned jets....). Could still be a lean problem...?
What gets me is that the temp soars immediately...as soon as you hit the throttle, the needle starts climbing.

BUDAH?

Do you have sea strainers? Mine did the same thing on one engine. Found the sea strainer about two thirds full of finely crushed shell.

First check the Sea Strainers if you have them.

Usually turns out to be a worn or damaged raw water impeller. It can flow just enough water to keep cool at low R's but at higher R's it cannot keep up. Also look at oil cooler.

Good Luck

Also if it is a bravo, check the elbow where the water pickup hose hooks to the transom assembly. These can become plugged or if the hose is loose you can suck air.

BT :cool:

My timing is at 10* initial with a 25* bushing in the MSD, so 35* total (in by 2800 rpm).
I`ve just replaced both head gaskets due to a small leak from coolant passage into cylinder.
I have not leaned it that much, (dropped 2 jets on rear, 4 sizes down on front) since prior lake runs. Plugs look fine.
I am suspecting a clogged oil cooler. If not that, possibly a worn impeller...

I don`t have sea strainers.
I am really suspecting the impeller or oil cooler.
I just replaced impeller in early part of summer. It might have maybe 25 hours on it. Could it be bad already? Could something have gotten in the pump and possibly damaged the impeller? Can a damaged impeller flow OK below 3500 rpm and then not keep up at R`s above 3500 ?
To check oil cooler, do I just need to disconnect hoses and back flush it?
Thanks guys, you`re very helpful!:)

Yes it is a Bravo One.
I will check the hose connection you`re talking about.
THANKS!

Sounds like a water shortage problem,either a bad impeller or a clogged oil cooler.

After I dredged the bottom with my low water pickup Bravo I limped to the dock. The high temp alarm went off as soon as I reached the dock. I replaced the impeller and housing and removed all hoses and back flushed the system. Felt pretty good about the job I did. Cranked it up on the hose and it ran perfect with normal temps. Put it in the river and went for a ride and it did exactly what you described. It would run at normal temp until I got above 3200 rpm and then it would climb. Any full throttle operation would make the temp climb rapidly. After returning to a lower rpm or idle the temps would go back to normal. After some head scratching and a couple of phone calls to a marine professional I decided to change the thermostat. That was it! It seems the thermostat was damaged by the high temps that occured after the sand sucking incident.

If I were you I would check the impeller and back flush the coolers. Then if you dont find anything replace the thermostat.

Good luck and post what you find.

Ron

The very first thing I did was replace the 160* thermostat (which I installed along with the new impeller in May) with a new 140* t-stat. It didn`t change anything....
I plan to take off the hoses and back flush the cooling system. I may as well replace the impeller. I can get a new Sierra replacement for $12.
I will let you all know when I get this figured out!

Sounds like an Oil Cooler is blocked if the Water pump checks out. Have seen it many of times !!

I haven`t had a chance yet to check out this problem. I do suspect a clogged oil cooler the most.
Here`s a question: If I had a sea strainer installed, would that catch most, if not all debris before it reaches the cooler?

As an inpellor goes south it will lose some blades. The blades go to the first cooler & stay there. They then block the water flow thru the cooler & the engine. Replace implellor, Then remove hose before first cooler & remove the rubber parts that are at the cooler. You may have to stick your finger in the cooler input to break the pieces free before you pull them out.

donman,l the Bravo's also have a plastic cone that holds the water intake hose in place one is under that elbow in the compartment the other can be seen when the drive is off. I had 2 collapse on different boats.You could check easily by disconnecting the hose for incoming water and run it bypassingt he regular intake. If you can get enough volume pumping through a garden hose

I had a similar problem. Would heat up at higher RPM's, but ran fine below 3800 and would cool right back down.

Decided to look at the impellar. It looked good but the housing had some minor scratches in it. Replaced the housing & impellar. That was it. Normal temps again.

The connection hose in the transom will also cause this, as it can become clogged, or it can loose is rigidity and collapse from suction.