new overheating problem

N

NOFATCHICKS

New Member
Jul 14, 2009
12
rockwall tx
ok.... first had the problem with the rpm/mph. changed props from 14 1/2 x 19 to a 15 1/2 x 15.. only because thats what the prop dealer recomended, probably because he wanted the sale an didnt have the 14 1/2 x 15 that i asked for. current problem.... installed the prop an works great im running somewhere between 4200 rpm and 4500 rpm at around 30 to 35 mph ( forgot the gps in my truck) but now after about 5 mins or so the boat started over heating. i pulled the bottom hose an put some back pressure to maybe blow out any clogs an putted back to the slip at a relatively warm temp. so my question is could the prop be the cause, or maybe coinsidence. impeller in the water pump, or water pump gone bad? any info on personal experience or current knowledge would be very helpful.... on a side note... does the alternator on my boat actually charge the battery or do i need an auto trickle charger?
 
Not sure about the over heating but yea the alternator should charge the batteries. with the engine running you should have 14.5 volts at the battery and the same at the sense wire at the alternator.
 
It's not the prop. You probably have a marginal raw water pump. The raw water pump is in the middle of the drive. It is a high pressure, low volume type. So it only needs to be a little worn for it to work less than properly. Haul the boat, split the drive, and replace the pump.

Best regards,
Frank
 
Fat,
Give us a little more symptoms of the over heating. Is it overheating at higher RPMs and then coming back down when you slow it down (exhaust manifolds)? Or does it overheat at idle and then cool off a little as you speed up (impeller)?

First thing to try is a new thermostat. They are cheap, you need the 142*. Then check for blockages from the hose coming in the transom, through the oil cooler, into the water circulating pump. If she's still overheating, set your idle to exactly 1000, pull the hose coming off the water pump that is supplied water from the impeller in the outdrive and put it into a bucket. Run the engine for exactly 15 seconds and shut down. Measure the water you have in the bucket, you should get 4 quarts. If you don't its your impeller. If you do its most likely your exhaust manifolds and/or risers or a stuck flapper in your Y Pipe.

I just had a brand new impeller go bad which caused me to overheat at idle and shutdown, but she would stay in the green if I was running at speed.

Good Luck!
 
I was running at around 4400 rpm for about 5 min when it overheated, I tried to blow the gunk outta the water line in from the transom. I let the engine cool down and headed back to the slip, on the way back when I had it at 3000 rpm it ran fine but if I gave it anymore the temp would rise with the rpm. Hope this helps
 
Fat,
Dosn't sound like an impeller, but I would change it next time its out just to be safe. Put the new thermostat in and if it still overheats with increased RPM's sounds like it could be the manifolds or risers.

Good Luck,
Billy
 
just a few things I would check before pulling stuff apart. I would check the temp at the location of the sender with an IR thermometer the reading should be within 10 degrees. if its a big differance it could be the sender or the gauge typical boat gauges, teleflex sender should read as follows through an ohm meter. 448 @100f +or- 10%, 128 ohms@ 160f +or- 7.5%, 46 ohms @ 220f +or- 5%, Check from a positive source, negitve leed on the ohm meter connects to the terminal on the sender. Maybe too much info but I like to double check things first so I know what I'm working with. Good luck and let us know what happens.
 
does it have a heat exchanger? sometimes they get all gunked up and causes the prob...(talking from experience with very similar symptoms) also..check all your hoses and thermostat..good luck!
 
i am a simple man so after reading all of that advice i say to you please check your belt tensions e.g. water circulating pump alternator etc.. if they are to loose they will slip at higher rpms and cause overheating hope i could help jimmy
 
When was the impeller last changed? If you don't know or know it is old I would change it first. Relatively simple and inexpensive to do yourself.
 
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