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Imracin68j

Yay, another overheating thread

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Imracin68j

Boat has been hitting the high temp sensor at idle if I'm idle too long.  Here's what I've done.  

Swapped out the impeller,
cleaned the lines exiting the impeller to trans cooler.
checked trans cooler.
back flushed from the trans into the pickup on bottom of boat
ran water from trans exit to impeller. 

Notables.  no heat coming from heater.
took thermostat out and it idles around 178.


Questions:  
how do I backflush?
Could sending unit be bad?
Can I run without a thermostat on the lake or will it be too cool once I get up to speed?
 

Edited by Imracin68j

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oldjeep

Pull the engine circulation pump and inspect it.  Sounds like it might be broke. (assuming your temp sensor is working right)

Edited by oldjeep

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Imracin68j

What and were is it?

 

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oldjeep
5 minutes ago, Imracin68j said:

What and were is it?

 

It would be called the water pump on a car engine.  Front of engine (nearest transom on a v drive)

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Imracin68j

Where is the sending unit located

 

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dlb
4 hours ago, Imracin68j said:

Where is the sending unit located

 

Next to the T stat.  The thing with the wire coming out of it.

I would check the circulation pump.  It should suck about 5 in about 15 seconds out of a bucket.  Do not test it with fake a Lake or other “pressured” intake system.  Hose pressure will mask the problem.

One thing to keep in mind is that more than one of us on this site have done all that you have done and then some only to put in another new impeller and problem solved....

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oldjeep
8 minutes ago, dlb said:

Next to the T stat.  The thing with the wire coming out of it.

I would check the circulation pump.  It should suck about 5 in about 15 seconds out of a bucket.  Do not test it with fake a Lake or other “pressured” intake system.  Hose pressure will mask the problem.

One thing to keep in mind is that more than one of us on this site have done all that you have done and then some only to put in another new impeller and problem solved....

The impeller is in the raw water pump and is what sucks the water from the lake.  The circulation pump is mounyed to the block. 

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Imracin68j

Ok, So I back flushed from the impeller back to the trans, tightened up all the hoses one more time.  Changed the gasket on the housing.  Drilled a 3/16 hold in the 160 thermostat and put it back in.  It feels like it's holding cooler now.  I have it at 169 now at idle.  Mind you, it's 109 here in Bakersfield.  I'll have to get it on the water to see what's up but I'm feeling better about it.  Hopefully I don't kill my chance with this client I have going out with us. 

 

 

Edited by Imracin68j

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formulaben
16 hours ago, Imracin68j said:

Ok, So I back flushed from the impeller back to the trans, tightened up all the hoses one more time.  Changed the gasket on the housing.  Drilled a 3/16 hold in the 160 thermostat and put it back in.  It feels like it's holding cooler now.  I have it at 169 now at idle.  Mind you, it's 109 here in Bakersfield.  I'll have to get it on the water to see what's up but I'm feeling better about it.  Hopefully I don't kill my chance with this client I have going out with us.

Outside air temperature is really irrelevant to an engine cooling issue; the temp of the lake can change it, but unless you're boating in a hot tub it shouldn't matter at all.  Drilling holes in the thermostat might bring the temp down, but it is masking the real problem.

In the picture at the bottom of the Overheating Guide you'll see an aluminum pulley.  That pulley is attached to the circulation pump.

https://www.dropbox.com/s/qyplhmhrp61nvc0/005B Overheating Troubleshooting Guide.docx?dl=0

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Pra4sno

If your temp sending unit is reading 169-178 and your high temp alarm is going off when it exceeds those temps then they are working.  My t-stat is a 160, my temp alarm is switched at approximately 180.  My water temp alarm was set up by Malibu and runs in series with an oil pressure alarm and trans temp alarm.  Any of the switches closing sounds an alarm. 

Important thing to note is the buzzer/alarm is a temp switch, and not a temp sender.  Temp senders are just lowering resistance as the temp increases and allowing more current through to the gauge/ECU.  Temp switch has increases internal pressure until a switch is tripped activating the buzzer.  Sender is $25.  Switches can be upwards of $100.   Old boats only have 1 sender and 1 switch.  New boats have 2 senders and 1 alarm switch.

I think woodski and formulaben have you on the right track with the circulation pump.  Not weird your heater isn't working - I don't know many who's do:  heater cores get blocked easily and as an accessory to the heating system they should not be looked at for restrictions to any critical flow or as an indicator to a restriction.  Usually its rust bits from the cooling passageways and a backflush releases them anyways. 

It's interesting your temps went down after drilling a hole in the t-stat, but were higher without the t-stat.  Regardless of how many holes drilled in it the T-stat will restrict flow vs an open thermostat manifold.  

 

One thing to take a look at that I've seen cause overheating at idle is if your sea water pump (impeller housing) has any drips or leaks.  If so, it is drawing air.  Opening and closing the housing to mess with the impeller can result in gasket leaks, and most of the plastic housings get cracks that can be hard to see unless they are dripping.

Edited by Pra4sno

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