Temp problem

[Will Fish]

New to the site, and I figured I'd give this a shot.

I have a 292 in-line 6 w/ and alpha 1 gen 1 drive. The motor is 3 years old, with 300 hours on it. Since I put the motor in, I have been running cold (no thermostat). The temp basically stayed at 125 deg at all times once warmed up. Last year I was running home, and my temp alarm went off and the gauge read 210. I immediately shut down and was assisted home. My immediate thought was my impeller, and since it was the end of the season, I came out of the water. I replaced the impeller and all associated seals and heat tube.

Went in the water this spring and immediately noticed my gauge rising. I took the riser and manifold off and flushed it out (they looked good with no blockages or scaling). INstalled them and started haing the same problem.

Pulled the intake and ran it into the bildge. Pleanty of flow. I then changed the raw water pump, eventhough the old one was new when motor was installed. On idle, the temp began to rise up to 165/170, but far much slower than it did previously. I went for a short spin. Once I brought her up to 2600-2800 rpms, she dropped to her normal operating temp. If I picked up the rpm to 3k or more the temp climbed again.

When I got back in, on idle the temp started to fluctuate from 130 up to 180, and continues to bounce back and forth. She even climbed up over 200. I do not believe I was running that hot because my alarm would have gone off. So, I changed the sender.

Now my temp on cold start was ver 200. There was no major fluctuation, and steady over 200. I changed the gauge and no change, still over 200. i ran new wires from the battery and sender as a sanity check, but no change.

I am now completely frustrated and lost. Anyone have any idea??????

 

[HT32BSX115]

Re: Temp problem

Howdy,


Welcome aboard!

Now my temp on cold start was ver 200. There was no major fluctuation, and steady over 200. I changed the gauge and no change, still over 200.

It's looking a lot like you have more of an indication problem vs an over heat problem.

The temp gage is just a simple ammeter (milli-ammeter)

12v connected to IT (the gage) and then the other wire goes to a variable resistor that reacts to temp (the sender)....... the circuit is completed through ground (the sender is grounded through it's metal housing)

Fluctuations can be due to poor connections in the sender wire AND poor ground connections (almost anyplace related)

Fluctuations-HIGH would be due to the actual sender wire touching ground someplace between the sender and the gage.......you can also get a bad sender right out of the box (although unlikely) and a bad gage.

That's where I would look!


Regards,


Rick

Oh, and by the way, you should NEVER run the engine without a working thermostat!!

 

[Will Fish]

Re: Temp problem

Thanks Rich

I know all of my connections are good, as I ran new wiring.

I am going to try changing the sender again and see what happens. I am hitting a brick wall.

 

[NHGuy]

Re: Temp problem

When you changed out the old impeller were any pieces missing? If so start opening up every conceivable part of the cooling system, back flush & blow it out. Do this where you can watch for debris. Like maybe on a white piece of concrete. Crud in the cooling passages is a bad thing.

Get yourself a laser thermometer and verify the temps are as reported to your gauges too.

 

[HT32BSX115]

Re: Temp problem

Thanks Rich

I know all of my connections are good, as I ran new wiring.

I am going to try changing the sender again and see what happens. I am hitting a brick wall.

Those senders have a specific resistance range that they're supposed to operate. It's not at my fingertips but you can probably find it easily. If you have an elcheepo multi-meter, just take the "old" one and put it in hot water with a thermometer and see if the resistance values match the temps.

Here's one for Teleflex gages... http://www.jamestowndistributors.co...TMTechCat-Instruments(v4_0)Tech Reference.pdf

 

[Will Fish]

Re: Temp problem

Ok so it turns out the sender was bad and now the gauge is working fine... but the plot thickens.

I ran off raw water and the temp slowly climbs to 200 after about 20 min. I hooked up my freshwater flush and ran the motor off both fresh and salt water. She ran cold 125. Took the fresh water off and temp climbed.

Took my I take off and had plenty of flow. Is it possible ny thermostat housing g is bad or clogged?

 

[HT32BSX115]

Re: Temp problem

Took my I take off and had plenty of flow. Is it possible ny thermostat housing g is bad or clogged?

You'll only know for sure when you pull it!

 

[Will Fish]

Re: Temp problem

So I went for a run , thinking I needed to flush it out. Temp was perfect at 2800 rpm or less. Anything over 2800 the temp slowly would rise. If I opened her up the temp climbed fast. Bring it down to 2800 and temp came back to normal.

I am lost. Might just bringg it to a merc dealer

 

[HT32BSX115]

Re: Temp problem

So I went for a run , thinking I needed to flush it out. Temp was perfect at 2800 rpm or less. Anything over 2800 the temp slowly would rise. If I opened her up the temp climbed fast. Bring it down to 2800 and temp came back to normal.

I am lost. Might just bringg it to a merc dealer

Marine engines of course, generate heat based on power output.

So more power means more heat.(and more rejection needed). If you are overheating at higher power settings, you likely have a total water flow problem. Do you have power steering? (power steering oil cooler obstruction.....)

This can be due to a bad sea-water impeller, obstruction(s) between the impeller and the engine, obstruction IN the engine, head, circulating pump, manifold, or exhaust-Riser, or in some cases the exhaust system (water-shutter burned up and obstructing the exhaust)

You didn't say if it's a salt water engine. Did you replace the manifold AND riser when the engine was rebuilt? AND did you check for obstructions in the Exhaust downpipe/transom area?

 

[Will Fish]

Re: Temp problem

Manifold ans riser were replaced with the motor. Other are clear and do not show signs of wear. There is no power steering and I replaced the impeller this year.

 

[Will Fish]

Re: Temp problem

Is it possible the impeller is bad, eventhough it was just done this year. It seams like I am not getting the right flow at higher rpms.

Also, on idle, the temp climbs after 20 min of 1200, yet when running/moving, I can get 2800 out of her without any problems.

 

[Will Fish]

Re: Temp problem

Marine engines of course, generate heat based on power output.

This can be due to a bad sea-water impeller, obstruction(s) between the impeller and the engine, obstruction IN the engine, head, circulating pump, manifold, or exhaust-Riser, or in some cases the exhaust system (water-shutter burned up and obstructing the exhaust)
QUOTE]

So far, I've replaced
1. manifold and risor new 3 years ago (with the rebuild) and I flushed them out, whith hardly any signs of wear
2. impeller this spring prior to launch
3. circulating pump about 2 weeks ago

I am unfamiliar with the water shutter. Can you shed some light on that?

Since I changed all the parts above, should I assume I have a blockage in the block or head? If so, how can I go about the repair? Replacement?

 

[skipper6567]

Re: Temp problem

Change the impeller. Ive seen this same issue dozen times. Ive learned the hard/dumb way. Just put a new impeller. Dont spend money on fancy lasers,exhaust, parts in the engine....ect.. this is a very simple system ie cooling.. trust me the impeller may look like brand new..just change it. dont worry about blockages from old ones breaking apart. dont worry about the shutter 90% of them are already in several pieces in the bottom of the y pipe.if the exhaust were blocked the engine would not run never mind cooling..also all the intercoolers that you may or may not have NEVER get obstructed enough to overheat, and that problem if it were to occur would happen over a long period of time. not run fine one day and the next overheat..will not happen. you get one of those plastic bags on your drive for 20-30 seconds and theimpeller is jusnk. you would not know it happend becuz when you see the overheat and back off the throttle the bag usually just falls off never to be seen. The shutters are important if the boat sits low in the water or older style exhaust. the newer style,mid mount risers never get water in em, they were more for the rear attached risers.Just do the impeller,dont need a water pump kit just the impeller.JUST DO IT!!It will fix ur problem..

 

[HT32BSX115]

Re: Temp problem

I am unfamiliar with the water shutter. Can you shed some light on that?

It's in your exhaust down-stream of the riser-elbow. It's there to (help) prevent water from "sloshing" from the actual water level in the pipe, up and into the riser either from either a rapid shutdown at high speed, or sitting with the bow on the beach and a wave coming by.

Volvo Penta has evidently redesigned their exhaust systems and/or decided they don't need them anymore. Mercruiser did no such thing......OMC is not talking!!...... Yes, if it's burned up/disintegrated, some or all of the remnants are sitting in the bottom of your exhaust Y-pipe(V-8) or Down-pipe(I-6), stuck in the exhaust bellows or somewhere else......OR pushed out the prop....

I doubt a missing shutter (blocking the exhaust) would cause an overheat. It WILL cause inability to reach WOT RPM because of exhaust obstruction.

If you replaced the Raw water pump recently it's possible that you made a mistake in the installation that is causing it to suck air (once on a plane)

I would go back through it.

Engines over heat because of LACK of water flow either due to a "bad" raw water pump or obstruction between the pump and the engine. It's not "Rocket Surgery"


Check your water flow. Put the boat IN THE WATER, remove the (raw water supply) hose from the transom and briefly run the engine. See how much flow you get.

Then add a piece of clear vinyl hose between the hose and the engine and run it. See if there's bubbles in the hose at various speeds..... That should point you in the right direction!


Cheers,


Rick

 

[Rocky_Road]

Re: Temp problem

Engineers design their engines to run with a thermostat for a reason. The main one is that without a thermostat the water can pass through the block so fast that it doesn't have the time to absorb the surrounding heat, and the block just keeps on getting hotter. You would never take your car's thermostat out, would you?

Way back when I was pulling wrenches on cars, a fellow came in with a constant overheating problem at any speed over a crawl. He had removed his thermostat on a whim, and a new one put his engine back to normal....

Just a thought!

Happy boating!

 

[Will Fish]

Re: Temp problem

Thanks for all the help... im going to try putting the thermostat in and check the flow through a clear hose (I pulled the intake and has plenty of flow o n idle). If that does not work I will pull the boat out, drop the lower unit, and change the impeller again. Will keep you posted. Thanks again for the info.

 

[tswiczko]

Re: Temp problem

Have you boiled the thermostat and measured water temp when it starts to open..
I had a tstat problem a few years back put it in hot water it opened fine
started with cool water and measured temp as it opened and found out it wasn't opening til above 180?F

 

[204 Escape]

Re: Temp problem

+1 on the impeller.

 

[Will Fish]

Re: Temp problem

I added a 6" piece of clear hose to my intake, and I am not getting good flow. She is fine on idle, but when I kick up the rpms, flow sputters on and off in 5 second increments. I changed the intake hose from the copper tube on the inside of the transom to the thermostat (thinking the hose may be collapsing. As you can see I am trying to avoid taking the boat out of the water.) This did nothing. So it has to be the ompeller.

So I pulled the boat, dropped the lower unit and changed the impeller, despite everything looking perfectly fine. Nothing. I am still overheating!?!?!?!?!?!?!?!?!?

I have no idea what to do now.

 

[Ky Baja Blast]

Re: Temp problem

I had the same problem on a 470 figured out my hose from gimbel to copper tube going Thur transom was bad