over heating issue continues.

[drtmnky]

1979 Sea Ray Sundancer 260 with 5.7 OMC 800.

I'm back with the same issue I brought here a month ago. The engine runs hot at about 1200 rpm and above.
I installed a low pressure gauge just before the heat exchanger and a ball valve at the discharge end of the hose. I tested the raw water flow through each of it's componants, and replaced worn hoses. There does not seem to be any impedence in the raw water flow.
I connected the discharge to one exhaust riser at a time, I capped the hose to the other one, and found no restriction through them individually. The riser having water flow through it would be cool, the other would be hot.
When I closed the valve at the end of the discharge hose for half a minute or so and then opened it the water would be hot coming from the heat exchanger.

But, it seems, I still have an over heating issue. I am going to replace the temp sender and probably also the thermostat again. This time I will test it before installing it. I may even replace the gauge. These items are low cost enough to replace and may be the easiest way to eliminate the wondering if they are functioning correctly.

I suspect they are not the culprit here. Do any of you have any suggestions of what else may be the cause?

Rob

 

[stevea661]

Did you ever check the various points on your cooling system with an IR gun like I suggested on your last post. Yours should be about the same as mine. To test the coolant temp sender, use an ohm meter and the IR gun, at 100f it should read 448 ohms + or- 10%, 160f 128 ohms + or- 7.5%, 220f 46 ohms + or - 5%. Remove the wire from the sender, connect one side of the ohm meter to the sender and the other to ground. If the gauge, sender, and the IR gun all agree, than you have a over heating problem. An IR gun costs like $40.00 from harbor frieght and is a real valuable diagnostic tool to have. If you are really getting hot you may need to have your exchanger rodded out like a radiator in a car.

 

[BonBini]

Worst case sinario is that you've blown head gaskets and or cracked heads. Lets not go there just yet.

Based on your latest symptom "The engine runs hot at about 1200 rpm and above" Coolant flow not enough for heat generated or too much heat generated for coolant flow provided.

First confirm you've got a problem by testing your instrumentation with another source. Easiest way may be to put sender in a metal can, jumper wired to your boat wiring, heat and test just like you've tested a thermostat. Do this on the boat.

After you've confirmed the instrumentation, let us know and we'll go on from there. ...Ron

 

[drtmnky]

Thanks guys for the info. I was wanting to know how to test the accuracy of the temp monitering system.
Steave, I did open up the heat exchanger rod and flush it. It is clean and seems to be in good shape.

Wouldn't the coolant level go down if there were a cracked head or leaking head gasket? I guess pulling the heads is not that big of a deal to verify all is in order there.

Rob

 

[Nehalennia]

I haven't read that you've verified your impeller is new. Do you know their condition?
Another consideration is a kinked, restricted or damage raw water supply hose.

 

[BonBini]

Yes the coolant level would typically go down and also get thrown out the over flow depending on how bad the combustion leak is. 240 deg water temp is pretty hot. At that temp it would seem your coolant would be purging out from the temp alone. Are you saying your not loosing any coolant? Does the coolant purge to the overflow tank seem right?

At this point of your trouble shooting process you need to test and not guess. Steve points this out above.

Some how confirm your gauge is close to being accurate and this thing is in deed getting hot and let us know. ...Ron

 

[wickedsearay]

is this in fresh water or salt water?
did you check your sea pump(impeller) to see if you are getting enough water coming in.
if you are in salt water check for any blockage at all water inlets and out you have a clogged hose.

 

[SCORPIO]

How old is the impeller?

 

[Chris Dauth]

Is the Temp. sender grounded ?? The Merc. thermostat housing gaskets have brass studs to ensure the sender housing is grounded to the intake manifold. This ensures the Temp sender is grounded. Automotive gaskets don't have the brass studs.
Gasket sealant material applied to the gasket during installation can cause a hi resistant joint even if the gasket has the brass studs.

 

[drtmnky]

This afternoon I completed another test of the cooling system. You are very right Steave, an IR gun is a must have tool to have in the tool box.

The test: Run engine with muffs, no prop for about 20 to 30 minutes at 1200 rpm and 3000 rpm.

Results: at 1200 rpm for at least 15 minutes the temp at temp sensor is 160. at 3000 rpm for at least 10 minutes the temp at temp sensor is 169.

The ohms, however, measured at 160 F is 99. I measured resistance between the outer jacket of the sender and intake manifold and got an almost zero reading, so it seems it is properly grounded. From what you tell me Steave i'd say the sender is bad.

I am going to pull the sender, inspect it and the port for it in the manifold and probably replace it.

Thanks for all your help guys, I will keep you posted.

Rob

 

[capecodcruiser]

just a heads up. I was told by a mechanic that a hose will not supply enough water to run a engine on the muffs above 2K rpm. You can hurt the lower unit impellor. Take it for what it's worth. Good luck

 

[stevea661]

This afternoon I completed another test of the cooling system. You are very right Steave, an IR gun is a must have tool to have in the tool box.

The test: Run engine with muffs, no prop for about 20 to 30 minutes at 1200 rpm and 3000 rpm.

Results: at 1200 rpm for at least 15 minutes the temp at temp sensor is 160. at 3000 rpm for at least 10 minutes the temp at temp sensor is 169.

The ohms, however, measured at 160 F is 99. I measured resistance between the outer jacket of the sender and intake manifold and got an almost zero reading, so it seems it is properly grounded. From what you tell me Steave i'd say the sender is bad.

I am going to pull the sender, inspect it and the port for it in the manifold and probably replace it.

Thanks for all your help guys, I will keep you posted.

Rob

You should have 0 or close to 0 resistance between the jacket of the sender and ground. the proper way to test is to remove the wire from the sender and check between the sender terminal and ground. As fluid temp increases, resitance decreases, running more volts to the gauge, making the gauge read higher. If you ground the wire to the sender it should peg the gauge. Not that you need to do this, because you already know the gauge works. You are just trying to see if it is reading properly and if not where the problem is.