OMC Cobra 5.0 overheating

[HT32BSX115]

Re: OMC Cobra 5.0 overheating


"What we have here is a failure to communicate"

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

All fresh water for me. It gets used 4-6 time a year. And when i'm done it comes home with me. Luckily my risers still look like new.

 

[Reinell-BRXL-191]

Re: OMC Cobra 5.0 overheating

OOOFF - are you not listening to me? exhaust manifolds DO NOT need to be cooled... yes, the water is injected in to the manifold, and it does cool it, but no one cares if the manifolds are cold or not... go out and open your hood of you car after a long drive and touch the manifolds.. they will take your skin off. if there was some importance of cooling the manifolds, then cars would be in trouble.. Sure, we don't want glowing red manifolds in our tight little engine compartment, so the effect of the injection at the manifold points, do in fact have a cooling effect, but they are also attached to a huge heatsink, they call an engine..The first item cooled by the water that is supposed to be cooled is the riser, the riser attaches to a rubber tube, that would melt if the riser was hot, then of course the water cools the rest of the piping until it exits the drive... the reason it is injected in to the manifold is so the exhaust pressure sends it down stream.. ONCE AGAIN, I am not saying that the manifolds are not cooled by the water, I am saying the first thing that is cooled that needs to be cooled is the riser... a hot manifold has no bearing on engine performance, and does not need to be cooled

My point here, was to combat your statement that the risers should be hotter than the manifolds, and there is no way in anyone's logical mind that could be true... say for instance you started the water injection at the point of the riser instead of the manifold, the force of the exhaust would carry the water down to the rubber piping before it could cool anything in the riser... the actual point of injection, even though cooled some by the water, has more effect on the areas down stream of it, then it does on the local area of injection. The manifolds are subjected to essentially a blow torch of 1200-1400 degrees depending on tune... they are always going to be hotter than the piping down stream. Exhaust on a small block flows anywhere from 400-600 cfm... trust me, that water is in the riser before it can do anything to stop the direct fire of a cylinder burn

Now, the purpose of water is to cool the rubber components of the exhaust system, so they don't burn up.. the reason they are rubber, is so they can be routed thru a hull, and not vibrate and destroy stuff... go, look at some speed boats... they don't give a damn about a 1500 degree header in an engine compartment... we only need to keep the rubber parts cold... the rest of it is no different than an auto exhaust.. it can be hot as ever...

and my 5.0 is a Ford, and OMC manifolds introduce water in all 4 exhaust ports, not just in to the front

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

. But i will say you are wrong on most parts. I will correct you on one thing though. Water is not injected into the exhaust stream in the manifold lihe you said. Is is a WATER JACKET design. same design as your block. The only time it enters the exhaust stream is at the risers.if it was injected as you sugest what happens to the water once the engine is off? Cars dont have cooled exhaust because the have unlimited airflow. Unlike a enclosed boat(water does help muffle sound also).my car doesnt have a mixture of wood vinyl and foam 2" away like my boat does. I apologize. For the spelling. I am on my pbone.

 

[sam60]

Re: OMC Cobra 5.0 overheating

This is very entertaining to me. Please keep it up! This is better than most "reality" shows.

 

[Reinell-BRXL-191]

Re: OMC Cobra 5.0 overheating

. But i will say you are wrong on most parts. I will correct you on one thing though. Water is not injected into the exhaust stream in the manifold lihe you said. Is is a WATER JACKET design. same design as your block.i apologize The only time it enters the exhaust stream is at the risers.if it waz injected as you suvgest what happens to the water once the enging is off? Cars dont have cooled exhaust because the have unlimited airflow. Unlike a enclosed boat(water does help muffle sound also).my car doesnt have a mixture of wood vinyl and foam 2" away like my boat does. I apologize. For the spelling. I am on my pbone.

I understand how an OMC manifold works.. I have one right here on my desk.. and have been staring at it the entire time of each of my posts..

you are just going to keep it up... but the fact of the matter is, the water is INJECTED ( means to put something inside of something else) in to the manifold, and the first thing it is supposed to cool is the riser, you said... the manifold should be cooler than the riser.. and you are wrong... I have no more interest in continuing this banter, there is no way, that something that is under direct fire from engine cylinders is ever going to be cooler than something being sprayed directly with 50-75 degree water out of a lake... don't feel it necessary to reply, because I won't even read it..

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

I dont think you understand how a manifold works. You said the water is injected into the four manifold ports. Then you said they dont need to be cooled which is wrong. Btw, The exhaust flows more than 600 cfm

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

Ran the boat for a few hours today, everything was perfect The temp gauge stayed at ~150 the whole time, even during short WOT bursts.
FWIW, I did take temperature readings after running the boat for about 45 minutes with the gun and although I don't remember exactly what they were, the risers were almost the exact same temperature as the manifolds (I believe it was ~100F starboard and ~85F port).

So to summarize; it appears that a faulty thermostat caused my overheat on Memorial Day, missing exhaust flappers allowed it to hydrolock, but nothing was damaged. After fixing the hydrolock and replacing the thermostat, I still thought it was running too hot, but it was actually just an incorrect temp sender.
The only mystery to me is that my impeller was absolutely shredded after I overheated on Memorial day... not sure how or why that would have happened. I suppose its possible that it was even the reason for the overheat, but I've never run the boat dry...

Thank you guys so much for helping me troubleshoot this, I really appreciate your help! This site has been invaluable. Between this and all the other work I've done, I feel like an OMC expert now
My boat thanks you as well:

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

I am glad everything worked out for you and that is a nice looking boat.

 

[sam60]

Re: OMC Cobra 5.0 overheating

Ran the boat for a few hours today, everything was perfect The temp gauge stayed at ~150 the whole time, even during short WOT bursts.
FWIW, I did take temperature readings after running the boat for about 45 minutes with the gun and although I don't remember exactly what they were, the risers were almost the exact same temperature as the manifolds (I believe it was ~100F starboard and ~85F port).

So to summarize; it appears that a faulty thermostat caused my overheat on Memorial Day, missing exhaust flappers allowed it to hydrolock, but nothing was damaged. After fixing the hydrolock and replacing the thermostat, I still thought it was running too hot, but it was actually just an incorrect temp sender.
The only mystery to me is that my impeller was absolutely shredded after I overheated on Memorial day... not sure how or why that would have happened. I suppose its possible that it was even the reason for the overheat, but I've never run the boat dry...

Thank you guys so much for helping me troubleshoot this, I really appreciate your help! This site has been invaluable. Between this and all the other work I've done, I feel like an OMC expert now
My boat thanks you as well:

I'm glad everything is working well, but I really enjoyed reading this post with someone (idle?) who would argue longer and harder than BruceB

Hope you have great times out there and that is a great looking boat! Maybe you can help me. I am having problems with this wax and low speed buffer of mine. I need someone to demonstrate onsite.

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

I dont like to argue at all. But if im pushed i will push back. But you know, his boat is fixed. That is all that matters. The rest is water under the bridge. Ill forget about it, no grudges and hope they do the same. I do appologize to the op for making a mess of his post.
Atleast i got my post count up a little.

 

[Reinell-BRXL-191]

Re: OMC Cobra 5.0 overheating

I dont think you understand how a manifold works. You said the water is injected into the four manifold ports. Then you said they dont need to be cooled which is wrong. Btw, The exhaust flows more than 600 cfm

Now who's spreading inaccurate info around the forum.. It's obvious that any time any issue is address that disputes something you have said, you just come up with something else to fight about..

I know I said I wasn't going to reply.. but man, you are just arguing to argue.. so, look at this 5.0 manifold, and tell me that the water doesn't enter in at the 4 ports?

also unless you have some hard core racing engine.. a 302-305 doesn't flow more than 600 cfm.. and if you wanted to break it down from side to side, less than 300 cfm out of one manifold and that's under perfect world conditions. I have been building engines for 30 years... its obvious you have not

A 300 cubic inch engine (302 c.i.) flows 521 cfm at 6,000 rpm.
A 330 cubic inch engine (331 c.i.) flows 573 cfm at 6,000 rpm.
A 350 cubic inch engine (347 c.i.) flows 600 cfm at 6,000 rpm.

 

[sam60]

Re: OMC Cobra 5.0 overheating

I dont like to argue at all. But if im pushed i will push back. But you know, his boat is fixed. That is all that matters. The rest is water under the bridge. Ill forget about it, no grudges and hope they do the same. I do appologize to the op for making a mess of his post.
Atleast i got my post count up a little.

Differing opinions provide more knowledge to the OP.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

All of this talk has been very informative, I don't feel you've made a mess of my thread at all.

 

[Ck111484]

Re: OMC Cobra 5.0 overheating

I'm glad everything is working well, but I really enjoyed reading this post with someone (idle?) who would argue longer and harder than BruceB

Hope you have great times out there and that is a great looking boat! Maybe you can help me. I am having problems with this wax and low speed buffer of mine. I need someone to demonstrate onsite.

What are you trying to do?
I just recently hit mine with a random orbital buffer using 3M Super Duty Compound, followed by 3M Finesse It II, then 3M paste wax; turned out GREAT.

 

[sam60]

Re: OMC Cobra 5.0 overheating

What are you trying to do?
I just recently hit mine with a random orbital buffer using 3M Super Duty Compound, followed by 3M Finesse It II, then 3M paste wax; turned out GREAT.

It looks great! My body is having problems keeping up with my ambitions.

Was it badly faded before you started?

 

[Reinell-BRXL-191]

Re: OMC Cobra 5.0 overheating

I can't believe you guys are screwing up my argument with normal forum talk.... stop it!

 

[bruceb58]

Re: OMC Cobra 5.0 overheating

Reinell, I will bet you $100 that if you put water into the tube at the bottom it won't go into the exhaust ports. I will send you my paypal address so you can pay me.

I say connect it to a hose and video it as proof. What do you say. You game?

 

[bruceb58]

Re: OMC Cobra 5.0 overheating

A 300 cubic inch engine (302 c.i.) flows 521 cfm at 6,000 rpm.
A 330 cubic inch engine (331 c.i.) flows 573 cfm at 6,000 rpm.
A 350 cubic inch engine (347 c.i.) flows 600 cfm at 6,000 rpm.

You may want a mulligan on this one too.

The numbers you are quoting here is the volume of the ambient air going into the engine which is basically the volume of the cylinders x RPM divided by 2. What you fail to realize is that the same mass of air is now heated to around 1400? after it has fuel put in it compressed and ignited so the volume goes up drastically while the mass remains essentially the same. That 600cfm will convert to almost 2000cfm in the exhaust manifolds....or 1000cfm per side. Just follows ideal gas law PV=nRT.

Even though I am a EE, I paid attention in my chem and thermo classes.

Not that any of this has anything to do with the OP and I am glad it was the sender and you figured it out measuring the temp with your IR tool.

 

[Idlespeedonly]

Re: OMC Cobra 5.0 overheating

I will give you one last poke before this thread gets closed. If the incoming cfm and out going cfm is the same an engine makes no power. You have been building engines for 30 years. I have not, so you know this already.

You had a problem with your boat not running right. You thought the factory designed exhaust bellows were restricting the exhaust. Then thought it was the ESA, but had to ask where it was? You have been building engines for 30 years. I have not, so you know this already.

Turns out to be a bad coil. But you have been building engines for 30 years. I have not, so you know this already.

You told the guy to use the rubber oring on the middle plug. Luckily someone stepped in before you gave this guy a nice little water leak. But again, you have been building engines for 30 years. I have not, so you know this already.

You tell someone that is trying to get his distributor in a chevy 305 "Not familiar with this particular motor, but on a Chevrolet, if you look in to the hole the distributor fits in to, you will see the the oil pump shaft sticking up, it has to be in the right position for the distributor to drop in at the location you want. otherwise, it just hits it, and sits on top and will not drop all the way down.. if the 5.0 is the same, this could be your issue"
Now a 5.0 is either a ford 302 like yours or a 305 chevy. Now someone building engines for 20 years and who owns a ford should know know how it goes in.

By the way, did you ever find the water leak? If not I can send my 11 year old son over to show you.

You try to insult my intelligence and knowledge, which I have no problem with that. You tell me I have not been building engines for 30 years like you have. You have no idea who I am or what my profession is.
But you know whats really strange after all of this, if you needed my help with your boat I would be the first one at your house to give you a hand. You may not want my help, But it would be offered.

Would you do the same?


I apologize for any spelling or grammar errors, my computer isnt working.