Overheating issues again

[akorcovelos]

I also think he's wondering why you replaced the water pump.

Oh, because I’m a dumbass. Nothing wrong with the circ pump. Feel good that it’s all new now though!

[SAB220]

akorcovelos - thanks for the reply. I agree remove the pump, work on the bench. Mine is FW thank GoD. Yes come in from the STBD remove the fuel/water separator filter, comfy moving blanket... hmm, circ. pump ...Main or Aux?

[akorcovelos]

akorcovelos - thanks for the reply. I agree remove the pump, work on the bench. Mine is FW thank GoD. Yes come in from the STBD remove the fuel/water separator filter, comfy moving blanket... hmm, circ. pump ...Main or Aux?

The circ pump isn’t even required with raw water cooling. They make bypass kits that just use the sea pump for cooling.

[Philgconnors]

I took apart the impeller and its in perfect shape. Flushed the intake hose and the output and water cane pouring out. Then I took apart the fuel and oil cooler and all the other hoses. All free from obstruction. Put it all back together and took the boat to the lake for a ride. It seemed better and was staying way cooler than before even up on plane and crushing a ways. It Seemed much better holding just slightly just under 175 at idle and and slightly above just above at crushing speed. Then I went to full throttle and it heated up to 250, however the motor was not that hot it’s really the exhaust manifold and risers that are so hot. Shut the boat off and restarted it 5 minutes later and it cooled right down to idle temperatures. So I’m not sure what the heck is going on. The things recently that have changed are as follows, new shift cable, new bravo3 outdrive from 1.81 gearing to 2.00, and a new thermostat. Boat ran great 3 days in a row after the bravo replacement, and then overheated after beaching the boat. I then replaced the thermostat. The valve covers and plenum all warm to the touch. It’s definitely getting plenty of water and cooling the engine. Any thoughts are appreciated. Thanks.

[Philgconnors]

I’m still thinking there is a problem. That engine should be running at a steady 170-180 at all throttle positions, and it’s heating up beyond that. Additionally those exhaust manifolds are running way hotter than I ever remembered them being. The problem is better since flushing the system but it’s still not right. Maybe the oil cooler is plugged up still?

[James]

I had the exact same issues with my 253, chasing all the things you already did. Not that this has anything to do with your issue, however in my case, it wound up being a collapsed plastic hose retainer holding the pickup tube to the outdrive transom plate that then passes through to an aluminum housing that the hose feeding the input of the pump connected to. I removed the two bolts that held the housing to the transom plate and could see the collapsed piece. In lieu of pulling the outdrive to replace (and Mercruiser has a kit specifically for this), I wound up installing a thru hull. Mechanic told me it was a known issue with the Mercruiser where corrosion caused the issue. Although water did pass, under higher rpm it simply could not provide the gpm (gallons per minute) water flow, thus the rise in temperature, stabilizing on idle and lower rpm. One other thing I advise, running that hot may cause the exhaust flappers in the Y pipe to disintegrate, make sure you check and I strongly advise replacing them or you could wind up with a hydro locked engine!

[Big Block Power]

I had the exact same issues with my 253, chasing all the things you already did. Not that this has anything to do with your issue, however in my case, it wound up being a collapsed plastic hose retainer holding the pickup tube to the outdrive transom plate that then passes through to an aluminum housing that the hose feeding the input of the pump connected to. I removed the two bolts that held the housing to the transom plate and could see the collapsed piece. In lieu of pulling the outdrive to replace (and Mercruiser has a kit specifically for this), I wound up installing a thru hull. Mechanic told me it was a known issue with the Mercruiser where corrosion caused the issue. Although water did pass, under higher rpm it simply could not provide the gpm (gallons per minute) water flow, thus the rise in temperature, stabilizing on idle and lower rpm. One other thing I advise, running that hot may cause the exhaust flappers in the Y pipe to disintegrate, make sure you check and I strongly advise replacing them or you could wind up with a hydro locked engine!

Is that what they call bravoitis? Yep with that drive being removed anything could be pinched or twisted. Maybe A7 will chime in. But he might tell you to pull the engine and go from there?

[Philgconnors]

“Pull the engine” are you kidding? That seems excessive. Would this condition happen that rapidly? Seems like it’s more of a “burst pipe” rather than a “slow leak”.

[Big Block Power]

“Pull the engine” are you kidding? That seems excessive. Would this condition happen that rapidly? Seems like it’s more of a “burst pipe” rather than a “slow leak”.

No it's a long story. I would have to search for his thread. But a dealer ended up twisting a hose and caused him a whole lot of grief for a summer.

viewtopic.php?f=47&t=527&hilit=Overheat&start=150

[Philgconnors]

Looks like the engine pull was necessitated by a snapped transom plate. After getting better water flow from flushing with the hose, I’m thinking there is something plugging the system most likely at the oil cooler. I’m going to start there and see what I can find. This is very frustrating as I’ve had nothing but problems with this boat since buying it.

[rabiddawg]

Phil, I’m in the same boat(pun intended ).

I finally got my 262 running strong only to find I have a cooling issue too. Mine runs cool all day but if I run it wide opens it goes into limp mode after a few minutes. My gauge only shows 175 when it dies this. It sits at 135ish otherwise. I’m gonna just enjoy it the remainder of this summer and tear into it this winter.

[Philgconnors]

Well I successfully fixed my overheating problem. I pulled out the oil cooler and sure enough it was full of some kind of plastic junk, rocks, and other nastiness. Cleaned it all out put it back together and went for a test run and it runs perfect at 175. No rise or fall at any throttle position.

[Big Block Power]

Well I successfully fixed my overheating problem. I pulled out the oil cooler and sure enough it was full of some kind of plastic junk, rocks, and other nastiness. Cleaned it all out put it back together and went for a test run and it runs perfect at 175. No rise or fall at any throttle position.

Good deal

[rabiddawg]

Glad to hear that!

I may yank mine out today while I await the seal kit for my power steering rebuild.

[akorcovelos]

Thanks for updating!