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mercruiser 5.7 1985, having problems with exhaust getting hot,motor stays cool,but elbow gets hot

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potatoe

New member
hello, i have a 1985 mercruiser 5.7, i just installed a new remanufactured longblock. the motor runs great. oil pressure good, tempature on motor and gauge is great. but the starboard side elbow(riser)connected to top of manifold is getting very hot between 150-190 degrees. it seems like its not getting enough water flow. i have installed new impeller and housing in outdrive, i put in a new thermostat kit, and im about to try a new circulating water pump(on front of engine). but im still getting same issue. the motor runs great, it does not overheat, but i know that it should not get hot. i put a brand new oem mercruiser manifold kit on engine. there is a difference from what was originally on this 1985 set-up. on the newer exhaust kit theres a different thermostat housing with only 4 hoses coming from thermostat housing and 2 of them going into bottom of manifold with water, and on the older set-ups, i see that theres an older thermostat housing with 6 outlets and hoses running water into the manifold and another hose going into elbow. so i dont know if i should try to convert it back to the old style, even though mercruiser told me that these newer style manifold kit (with water hose running into manifold only) will be fine. i am stumped. unless theres a defect some where, i cant figure it out. the motor does not overheat at all, keeps a nice tempature, and runs great, but that one side should not be getting that hot. i dont know if im getting the wrong information or what. but listen to this, when i bypass the outdrive and force water in by hooking hose up to the water inlet that comes from outdrive(transom), it then runs cool and normal. thats why i thought it was the impellar on outdrive, but i installed a new kit and same issue. i dont know what else to try besides the circulating pump or try to go back to the older way with the 6 way thermostat housing and run hoses directly to manifold and to riser/elbow, instead of now with just 1 hose pumping into bottom of manifold. if im confusing anyone please ask me any questions. because i am confused as hell. i have been getting mixed info, and try to stick to the certified experienced mechanics for info,but still getting different info. if your wondering why i didnt stick with the older set-up, its because i was told they dont make them anymore and that these are better. and you can get the older style if you want, but its aftermarket only and not oem. i would think there was a clog somewhere, but it runs cool when i hook hose to motor and not the outdrive. thanks in advance for any help.
 
Ayuh,.... I donno how you can read that alphabet soup,... It makes my eyes bleed,...

A paragraph or 2 would certainly help,...
 
Docksidemarineservices said:
Look for a blockage (old exhaust flapper) stuck in the Y pipe or in the drive.
Click to expand...

yes, we checked the flappers. i dont understand if there was a blockage some where, then why does it run cool and fine when i hook up water hose directly to engine instead of the muffs on outdrive,unless theres a blockage in outdrive or transom somewhere. ive also installed brand new bellow kit with water hose, and new impellar and housing kit in outdrive. when outdrive was split in half, we checked and blew air threw water inlets and seemed fine.and it does the same as before impellar kit was installed. is there anything else in the drive that could cause this? i know that with garden hose directly hooked to engine, that it forces it in with the garden hose pressure, thats why i was gonna try the circulating pump. but it looks newer and is pumping water. it just seems like there is a flowing,pumping issue, not getting enough water or pressure. and i have tried with boat in water with same problem just incase the garden hose wasnt producing enough water. this is new engine, new manifold and elbow kit(mercruiser oem not aftermarket), new thermostat kit, new bellow kit, new impellar and housing kit in outdrive. the boat drives and runs fine, and the tempature on engine gauge reads normal around 120-160 degrees. the only way to tell is by touching the starboard side elbow or using infared thermometer, and it gets up to 180-190 degrees. and again, the problem does go away and elbow stays cool when garden hose is hooked directly to the motor .
 
The garden hose is no way to check cooling system performance. A lot of air is pumped in along with the water. Drop it in the water and watch your problem disappear.
 
unless theres a blockage in outdrive or transom somewhere
Click to expand...
Look inside the fresh water pass thru on the inside of the transom where the water inlet hose attaches. There may be some mineral buildup in the pipe.
 
A tried and proven over-heat trouble-shooting method, is to follow the sea water path from point of entry, from component to component until it reaches the exhaust elbow and mixing chamber, and on out the drive or hull, etc.

Look at each component methodically and systematically as though you were the sea water......., and we'll usually find the problem.



And I agree....... your text would be much easier to read if you'd break it up into paragraphs, and use some spaces between stop and start.
No offense!



.
 
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