5.7 liter Alpha 260 over heating wide open throttle

OK, I have re sized this so that it is easier to understand. I am on my 3rd engine in the past 4 years. I keep loosing them do to them over heating too many times. Each time they have over heated I have had to change the oil because of the lose of oil pressure and the cooking of the oil from the severe heat.The over heating mostly happens at wide open throttle for 30 seconds the temp will shoot up to 200-220 and suddenly drop to zero and that's when she is running hot. O degrees and you hear the engine pining.

I just put in the 3rd engine on Thursday and took the boat out on the water Friday and Saturday. Friday she ran perfect all day long. I put about 10 hours of run time on the fresh engine. Saturday we took it out again and drove it 13 miles down the lake and she was fine. I decided to take it up to 3/4 throttle and the over heating scenario happened again 220 and then 0. I shut the engine off and you could just hear the engine crackling and bubbling from the heat. The engine got so hot that it melted the plastic elbow shut for the crankcase vents.

Each engine has a new thermostat and new impeller and new engine circulation pump for a serpentine belt. Yes the belt is routed the same way as designed.All three engines had different intake manifolds. The only things that remain the same are the hoses which I have verified that they are clear of blockage and the heat exchanger for the power steering which is clear too. I have the original exhaust manifolds on the engine and the original rises.I currently have the rises off the engine and you can see they are not rusty nor do I see any blockage

Can anyone tell me by looking at the photo of the thermostat housing, is the plastic sleeve installed correctly?I was missing this on the first engine from the previous owner replacing the t stat.

One other thing I did notice when the second engine went was when I split the outdrive to inspect the impeller I noticed the tube coming out of the upper housing of the impeller had a dimple in it and it did not line up correctly to the housing when reinstalling the drive. I had to pull it down to make contact with the o rings inside the housing. Could it be possible that the dimple is causing the pipe to push out of the pump and fill the cavity up in the out drive and starving the engine for water?
Mike

Re: 5.7 liter Alpha 260 over heating wide open throttle

revised with pictures

Re: 5.7 liter Alpha 260 over heating wide open throttle

are you sure the engines arent leaning out starving for fuel on top end causing them to over heat .... and does the motor stay cool at lower throttle positions ... i would think that if it wasnt cooling at all it would get hot real quick and if you have replaced the impellors my next step would be to check for water flow to thermatat seeif its getting water there then remove the thermastat and see if it runs hot

Re: 5.7 liter Alpha 260 over heating wide open throttle

oh also i had a friend one time with a similar problem and his lower hose to engine was collapsing at full throttle because it didnt have a spring in it effectivly cutting off water flow at wot ... he put a hose on it with a spring and it fixed the problem ... easy enough to check ... pull engine shroud and watch the hose at full throttle and see if it collapses

Re: 5.7 liter Alpha 260 over heating wide open throttle

Could it be possible that the dimple is causing the pipe to push out of the pump and fill the cavity up in the out drive and starving the engine for water?

Click to expand...

Ayuh,..... Absolutely....
That's why you should have been doing Tests,+ Diagnosing the overheat issue,...
A couple of motors ago....

How do you run a motor That Hot,..??
It sounds like your break-in/ testin' consists of Mashin' the throttle,+ Run 'er til she Blows,..??

Re: 5.7 liter Alpha 260 over heating wide open throttle

defer to Bond-o. He da guru.

Re: 5.7 liter Alpha 260 over heating wide open throttle

Bond-o said:

Ayuh,..... Absolutely....
That's why you should have been doing Tests,+ Diagnosing the overheat issue,...
A couple of motors ago....

How do you run a motor That Hot,..??
It sounds like your break-in/ testin' consists of Mashin' the throttle,+ Run 'er til she Blows,..??

Click to expand...

I'm looking for help not more problems. If your that good how about helping not starting a fight??

Re: 5.7 liter Alpha 260 over heating wide open throttle

chaparall villain 2 said:

oh also i had a friend one time with a similar problem and his lower hose to engine was collapsing at full throttle because it didnt have a spring in it effectivly cutting off water flow at wot ... he put a hose on it with a spring and it fixed the problem ... easy enough to check ... pull engine shroud and watch the hose at full throttle and see if it collapses

Click to expand...

Thanks I will try it in neutral but my condition only happens under way. I do know that the hose does not have a spring it in to prevent it from collapsing. I am going to try and find a spring tomorrow for the pipe.
I did pull the heads off today and found the gasket was seeping between the cylinder 3-5 The head seems to have warped from the heat so they are going to get magna fluxed and decked tomorrow.

I separated the out drive again and the tube has popped to the left again and I got with a local marina and their tech stated he has only seen this once before and it was caused by a thin plastic sleeve that fits on the copper tube which melts if the impeller goes bad and possibly disappears. and the coupler does not fit tightly on the pipe causing the pipe to pop off the housing on the alpha one gen II and starving the engine for water and causing the gauge to drop to zero.

Mine is missing the sleeve, I am suspecting this as my culprit. I bought the sleeve, new pipe and coupler with o rings

Re: 5.7 liter Alpha 260 over heating wide open throttle

People always seem sooo reluctant to replace their elbows and manifolds, even when they have an over-heating problem. They are standard disposable items that should be changed regularly anyway......and soooo much cheaper than a new engine.
My over-heating problem (high rpm) turned-out to be a defect in the material (rubber) of my Sierra impeller....I'm waiting for the response of my warranty claim. That was a tricky problem to solve....because impeller was NEW.
I also had a engine circ pump fail, the impeller broke loose of the shaft, and the temp gauge went to 0, yet no water was circulating through the block.
I'm on my 3rd t-stat housing on a 1991 boat, saltwater cooled.
Replace hoses with clear vinyl to see the flow.
Try running with no T-stat, just as an experiment.
Replace elbows/manifolds. Replace circ pumps, etc.etc... and any impeller.
You can try to properly diagnose a cooling problem (without blindly replacing components), but sometimes they can be very very tricky.

Re: 5.7 liter Alpha 260 over heating wide open throttle

Thanks I went out and bought a clear hose for the drive to block to see if I loose flow or if it is air rated. I did talk with a few guys at Prince William marina and they told me to check and see if there is a split in the hose from the drive to the transom. They had run into this where once the engine is at 3/4 throttle or higher and you trim the drive the hose split will open and you loose water flow. They told me they see this at least once a month running the boats on the Potomac river from floating debris. Thanks for everyone's advice I have a huge list of things to do on the boat tomorrow and hopefully she will be fixed once and for all and I can enjoy it this week end.

Re: 5.7 liter Alpha 260 over heating wide open throttle

That hose is a pain to change but it has to be right and could easily be your culprit. Mercruiser says to change it by removing the through-transom-tube, fitting it to the new hose, then putting the tube back into the transom. This is done with the drive off, and it's even easier with the bell housing off the pivots. Then you want to get the hose length just right so it won't kink or overstretch.
If someone can recommend an easier way, good for you. I hate doing that job.

Re: 5.7 liter Alpha 260 over heating wide open throttle

H2recovery said:

Mine is missing the sleeve, I am suspecting this as my culprit. I bought the sleeve, new pipe and coupler with o rings

Click to expand...

Without the sleave, there is nothing to seal between the pump and the tube. You were loosing allot of water right there.

Re: 5.7 liter Alpha 260 over heating wide open throttle

The Boat is fixed. Heads tested good and the engine is all back together. I did find the feed tube in the drive unit kicked to the left again when I separated the drive half's. I compared the brass tube with the new Plastic tube and the brass one is almost 1/4 shorter than the new tube. This would explain why the engine is starving for water and the tube keeps kicking to the left.I replaced the tube and both o rings on the impeller housing along with the sleeve and the new upper tube seal.

The good news is the engine runs a continuous 185 degrees and no over heating.

Thanks for everyone's help.