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Old 06-18-2017, 07:44 AM
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Default tempeture gauge flucuates

i have 500hp"s on one of the motors the temperature gauges fluctuates will go from the low reading of 100 to 150 stay there for i lttle bit then back down to the low reading of 100 the back up to 150 or in between i have replaced the water pump impeller and the thermostat how do you check the sending unit., are any other suggestions

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Old 06-18-2017, 07:55 AM
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Check the connections to all the electronics. In addition, while I'm not a mechanic - SO PLEASE DON'T TAKE THIS AS GOSPEL- I've been told that if you have wild variations of temperature - up/down-up/down - it could be pointing to a head gasket -- again I'm not a mechanic and I don't want to scare you. Another item was the thermostat you installed the correct temperature range? We have a 7.4 MPI and our temp stays pretty constant around 165-170

best of luck

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Old 06-18-2017, 08:26 AM
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swap the 2 senders. if they are in the thermo housing, mebbe swap the 2 housings. but it sounds like water flow. pull thermo hsgs and clean out. backflush incoming raw water hose. but separate and flush each piece separately. if there are 2 coolers on there, you hafta open up between them and flush the one that gets water last so that it doesn't push the junk into the other one. then pull hose at transom and flush first cooler so water and gluck comes out there. then put a hose on transom fitting and flush out the transom assy, preferably with drive removed, but not absolutley necessary.

Last edited by dereknkathy; 06-18-2017 at 08:35 AM.
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Old 06-18-2017, 02:24 PM
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Adding some other possibilities not mentioned here. That also can be the signs of having a bad water circ pump. And or air entering into your cooling system and or restrictions in the cooling system and or a T stat problem.

We use the clear hose testing method and look for air bubbles in the sections of the cooling system to pin point the area of the problem(s).

Will add can not tell you how many running around with a sub par working water circ pump especially without closed cooling - have no idea why owners never changed them out as an maintenance item of so many years they are good for in a marine application, especially when you can buy one. made in the USA for under 200 bucks.

I get mine made here in the USA so for those needing any let me know. They are Marine rated 100 percent.. These are NOT Sierra poor casting pumps and they are NOT GM Auto pumps either.

Last edited by BUP; 06-18-2017 at 02:50 PM.
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Old 10-14-2018, 05:35 PM
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BUP was right after spending quite a bit of time messing with this issue as a I decided to replace the circulation pump, figuring what the heck its the original pump and probable do any way I did take the back inspection plate off the back to see if there was anything obvious. there wasn't all the vanes were in tack no obstruction not sure what causes this but I put a new pump on and have not had the problem since. thought I would post the results to help others that might come across this problem.

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Old 10-14-2018, 07:11 PM
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thanks for posting the fix. So glad to post that was accurate info on my part to help and help others - want to ask did you check this out after I posted the possible issue ( the water circ pump ) way back then ?

. Just hopefully I can gain more market share with the USA made water circ pumps that I have made, but just has not caught on with most up here. Wished you would have grabbed one from me from the start especially with the info to help with fix and spot on.

clear water hose testing after your impeller housing -- more so closer to the front of the engine for placement -- if water with air bubbles in the hose most likely you need a new water circ pump and or leaking air into the water flow and or a restriction impeding water flow .

Last edited by BUP; 10-14-2018 at 07:19 PM.
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Old 10-15-2018, 12:32 PM
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I was going to ask about the thermostat housing gasket.
Read quite a few times about needing the brass inserts for conductivity between parts.
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