Thermostat ?

[Eddie Ray]

Aq125a. When the engine gets up to around 180degrees,should the water in the expansion tank be flowing thru the engine block? Had the muffs on, and watched. It seemed like the thermo never opened . The water in the tank was warm, but did not seem to be flowing? Also,if I add water at the stainer housing with a hose,where should it come out?
There was a little water coming out the exhaust ,but it was more like a mist or steam?
Thanks for any help.
Eddie

 

[billbayliner]

Re: Thermostat ?

Eddie, there are two sides to your cooling system. The water in the expansion tank [heat exchanger] is antifreeze coolant and it will flow through the engine block. It may take several minutes or more for enough heat to build and open the thermostat. Not much will flow until the stat opens.
The other side is the sea water side that flows through the strainer and into the heat exchanger and then out the exhaust. It would like air passing through a car radiator and pulling the heat from the antifreeze coolant.
If you added water directly to the strainer you'd be bypassing the sea water pump and could ruin the impeller.
You should be seeing a good flow of plain water from the exhaust when running on the garden hose. If not, then you may have a sea water side problem; bad impeller, suction leak, bad water neck fitting, etc.

 

[Eddie Ray]

Re: Thermostat ?

Okay,so with the cap off. The muffs on. Once the engine is at op.temp,the thermo should open and the fluid level should drop in the res.tank? I drained exp. Tank . Filled it ,and with muffs on ran until it reached 180or so degrees. The thermo should have opened,and the level of fluid should have dropped as fluid ran thru block .right? This did not happen. So I assume the thermostat is not opening as it should,and needs replaced. Would you agree? Can it be safely ran with out the thermo stat?
Thanks for any info or help
Eddie

 

[Maclin]

Re: Thermostat ?

Why would you expect a fluid drop in what you call the res. tank?

 

[Eddie Ray]

Re: Thermostat ?

Accordding to the book.when refilling the tank with coolant. You should fill to within one inch of the top.run the engine to operating speed.at which time the thermstat will open and the block will fill .then you need to top it off.let it run a few minutes more with the cap on..let it cool down . Remove cap and check fluid level.top off if needed? That is what the book says. I don't know for sure that is why I am at this site asking? If you think this is incorrect please let me know,the book has been wrong before!
The boat is running a little hot. I have flushed out every thing.seem to have good flow. Used to run her on the muffs with no problem.
Just seemed to me like the thermostat was not opening allowing the motor to cool?
Thanks for any help,this site is a life saver.
Eddie

 

[captmello]

Re: Thermostat ?

Those engines are supposed to run up in the 180s-190s. Did it just start running hotter recently? Sometimes the gauges are not as accurrate as we would like. If you have an IR temp gun, you can shoot the temp at the thermo housing to see what temp its at, or shoot the base of the temp sending unit and compare temps. There are many reasons that can cause these engines to overheat, or run hot as Billbayliner mentioned. The level in the expantion tank will vary as the fluid expands and contracts with heat.

 

[billbayliner]

Re: Thermostat ?

Eddie, think of this as though it's a car radiator. The engine and radiator will be full of antifreeze. Any air bubbles should purge once it has cycled a warm-up and cool-down. Top off as needed as per your book.

The coolant [antifreeze] circulates through the car radiator [heat exchanger] to dump accumulated heat after the coolant has circulated through the engine.

The air passing around the radiator tubes does the same as the sea water does in your Heat Exchanger. It removes this heat, and then allows the coolant to re-enter the engine. The thermostat holds coolant back until the right temp is reached.

The air is constantly being changed with fresh cooler air. [this is your sea water]
The air and coolant [or sea water] never come in actual contact with one another.
The antifreeze simply continues to circulate and the cycle repeats on a continuous basis.
The antifreeze side will be a "No-Loss" if all is working.

You have two caps. 1 for the antifreeze side and 1 at the sea water strainer.
I would not remove either cap while it's running.

I wouldn't necessarily look to the thermostat for your problem without first seeing that the heat exchanger is clean on the inside, exhaust manifold is flowing sea water, the sea water pump impeller is good, and that you don't have a suction leak.

When was the last time you replaced the water neck fitting and gasket?
Is the lower pivot tube o-ring good?
How about the upper pivot tube bushing?

 

[Eddie Ray]

Re: Thermostat ?

I recently run into some mud . And since have had a cooling issue . It was recommended that I flush and back flush the system. In that process some of the coolant was lost. I decided to replace all the coolant. I checked for water flow thru everything,and checked the impeller . Before the mud incident,never had any heat problems at all . Stayed at about 185/190 all the time. So now I am trying to get her back to where it should be. A thermostat is inexpensive and easy to do ,figured it wouldn't hurt and might help the problem.
On the muff,there was never a great out flow of water. From what I have read here that is common. But before on the muffs she did not get hot. Now she dose. I do not let it get much over 190 before shutting it down.
Thanks again for all the help.
Any ideas will be appreciated.
Eddie

 

[billbayliner]

Re: Thermostat ?

Eddie, while on the muffs, you should have just as good a water flow as if in the water and especially at low rpm as long as the supply is good and you are using the right muffs for the Volvo and you are pluggingg the drain hole.
If it wont' pull water up and through the drive while on the muffs, then you might have a suction breach.
Could be the water neck fitting/gasket, could be the o-ring at the bottom of the pivot tube, could be a hose connection, or it could be that you lost the seal at each thrust surface at the impeller.
Sand and silt can be very abrasive to the impeller and brass pump body.
None of this sand or silt should have affected the antifreeze side of the system, only the sea water side including the sea water side of the heat exchanger. This is why I'm thinking that the thermostat is not the problem.

If this was the car radiator example, you're chasing down an air flow problem, not an antifreeze coolant problem.
IOW, the sea water side!

 

[Maclin]

Re: Thermostat ?

Eddie,

I see now what you were looking for during the refilling, and yes fluid should drop as the thermostat opens and the block fills, sorry! Once full and all air purged as mentioned before, the fluid would just move around but not drop.

 

[Eddie Ray]

Re: Thermostat ?

Thanks guys for all the help. I went ahead and changed the thermostat. One less weak link in the chain.... It did not fix the problem as you predicted. However! I did find what I think is the problem........ On the intermediate housing,the water connector is broken. This makes total sense to me. When going slow,this connection is under water and not a problem.things stay cool. Once I speed up and the boat starts to plane this fitting is rising up out of the water. An thus is drawing air and causing the heating up problem.
Dose this sound right to you? Looks to be an easy fix . If there is anything else , you think I should check let me know.
Like I said earlier ,before the bog down in the mud. She was running well and never hot. She still runs well,and I think fixing this leak should do the trick.
As always thanks again,you guys are great
Eddie

 

[Maclin]

Re: Thermostat ?

Eddie,

Your symptoms certainly align with a problem with that connection. If it can suck air at that point then the cooling system will definitely not be getting enough raw water when the boat is on plane.

 

[billbayliner]

Re: Thermostat ?

However! I did find what I think is the problem........ On the intermediate housing,the water connector is broken. This makes total sense to me. When going slow,this connection is under water and not a problem.things stay cool. Once I speed up and the boat starts to plane this fitting is rising up out of the water. An thus is drawing air and causing the heating up problem.
Dose this sound right to you?

This is the water neck fitting that I mentioned. It is a very typical problem and easy to fix.
The beaded side of the gasket faces downward onto the pivot with just water proof grease on the bead.
Use sealant on the flat gasket surfaces if you want to.

 

[Eddie Ray]

Re: Thermostat ?

Thanks guys. If not for this forum ,and reading it often. I would never have connected that problem with the heating issue. I thought I had check all the usual places I could have a leak? But this one really made sense when I thought about it.
Thanks, I'm sure there are tons of people out there that would be lost with out this forum.
Looked up the part and bought it here.
Thanks again
Eddie