Overheating problem. Any help would be appreciated!

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backwoodsnwater
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Overheating problem. Any help would be appreciated!

Postby backwoodsnwater » Mon Jan 02, 2017 8:22 pm

Just bought a boat with a very fresh 500 Cadillac dd, boat will stay in the 160 range on temp for anywhere from 10 -30 minutes then burp out about 2 gallons of water then start running hot. I can let it cool completely back down and add about 2 gallons of water and it's the same thing over again. Previous owner said it had a 14-15 PSi radiator cap and he went to a 19-20 and thought the problem was solved. My question is should I try a higher pressure cap than that or what else could cause this problem?

backwoodsnwater
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Re: Overheating problem. Any help would be appreciated!

Postby backwoodsnwater » Mon Jan 02, 2017 8:34 pm

Not burping it out of the actual radiator but the reservoir up top into the overflow tank then out.

SWAMPHUNTER45
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Re: Overheating problem. Any help would be appreciated!

Postby SWAMPHUNTER45 » Mon Jan 02, 2017 8:35 pm

What did the engine builder say when you brought it to him with the broken starter issues?

Reason why I ask is it could be related

backwoodsnwater
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Re: Overheating problem. Any help would be appreciated!

Postby backwoodsnwater » Mon Jan 02, 2017 8:53 pm

Haven't had a chance to talk to him with the holidays and all, put a top of the line napa high torque starter on and so far no more starter problems. From what I was told he(the builder) is the one that said go to the next highest psi radiator cap.

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glades cat
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Re: Overheating problem. Any help would be appreciated!

Postby glades cat » Mon Jan 02, 2017 9:04 pm

I helped a buddy with a similar coolant loss problem. Found the aluminum reservoir had an irregular surface where the cap gasket seated. It wasn't the top surface, it was the bottom one. I put a grinding wheel of the same size on a drill and ground it flat. It seated well after that.
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backwoodsnwater
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Re: Overheating problem. Any help would be appreciated!

Postby backwoodsnwater » Mon Jan 02, 2017 9:09 pm

Thanks for the input Glades, I'll check that soon as I get back to the boat.

backwoodsnwater
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Re: Overheating problem. Any help would be appreciated!

Postby backwoodsnwater » Mon Jan 02, 2017 9:12 pm

But on a different note, are there any safety issues with going with too high a psi cap?

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Deano
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Re: Overheating problem. Any help would be appreciated!

Postby Deano » Mon Jan 02, 2017 9:29 pm

Going to the next step cap is not uncommon, however if you are already at 20 lbs and having issues, the time has come to determine what the problem is. Glades Cat offers worthwhile advice about that seat. Beyond that . . .

Where the cooling system on that engine is concerned, you HAVE to do one of two things. Either run a Cadillac thermostat or if you do anything else (thermostat or not), the bypass below the thermostat needs to be plugged with a one inch freeze plug. I would presume the engine builder is/was aware of this, so if yours doesn't currently match that scenario one way or the other, somebody has been there after he set it up. :dontknow:

I only point this out, so you are aware of the fact of the matter. Not pointing fingers at anybody, just making you aware of a Cadillac difference that will render those results when and if one of these methods is not followed.

Given your starter mishap and shut down characteristics, there seems to be a good possibility that your timing is not what it should be. If that is/was the case, it could possibly have a blown head gasket which could also provide the results you describe.

Were it me, I would first pull the thermostat housing and identify what you do or don't have under there.
In the event you find a standard Chevy thermostat (or no thermostat) and no freeze plug underneath it, that is your problem, without a doubt.

If that scenario is according to Hoyle, then performing compression and leak down test will help determine if you have a bad head gasket.

In any case, I would then double check the timing. Detonation is your biggest & easiest prevented enemy.
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Deano
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Re: Overheating problem. Any help would be appreciated!

Postby Deano » Tue Jan 03, 2017 9:15 am

I got a PM questioning the 'missing freeze plug', but will answer that inquiry here so whoever else may have the same question can benefit from the answer.

The Cadillac block has an internal bypass that recirculates water through the entire block until the thermostat opens. This allows it warm up more thoroughly than do other configurations used by others. The Cadillac specific thermostats are constructed in such a fashion that they plug this bypass when they open. This re-routes the flow from inside the block to the cooling system at large. The potential drawback is that these 'Cadillac specific' thermostats were only available in 180 and 195 temp versions. A little to warm for my liking on an airboat.

The thing to be aware of is that if you do NOT use the Cadillac thermostat, you MUST close that bypass or the coolant will not be routed to the cooling system. It will just recirculate in the block until it overheats.

My preference is to plug the bypass and run a generic (I prefer STANT) 160 degree thermostat.
Admittedly, this could be an entirely additional debate that needn't be here for this purpose.
What is Not debatable, is that without a Cadillac specific thermostat, the bypass MUST be plugged.

Naturally, if you do the later, you should drill a small (1/8") hole in it at the front, so it can burp air when you fill it.
Basically, that all boils down to this:

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nebraskaairboater
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Re: Overheating problem. Any help would be appreciated!

Postby nebraskaairboater » Tue Jan 03, 2017 10:17 am

are you sure you got all of the air out of the block when you filled it with coolant? If not it will flash boil the coolant in the heads causing it to burp like that. I would take some time and make sure you get all of the air pockets out. The reason I suggest this is you say a very fresh rebuild. It takes some time to get all of the air out of these motors. If you have a head gasket issue it could also over pressurize the cooling system. Happened on my dad's Olds boat a couple of times.
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Re: Overheating problem. Any help would be appreciated!

Postby One Eyed Gator » Tue Jan 03, 2017 11:54 am

I ran the set-up that deano described bit I used a gutted thermostat. Also ran a large dual pass radiator. Never got 170 and ran around 150 unless I was running it hard.

I never ran an expansion tank either. Worked great for the 10 years I ran it.

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Re: Overheating problem. Any help would be appreciated!

Postby BigDaddyT » Fri Jan 13, 2017 9:41 am

Excellent detailed explanation Deano.
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SWAMPHUNTER45
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Re: Overheating problem. Any help would be appreciated!

Postby SWAMPHUNTER45 » Tue Jan 17, 2017 7:24 pm

This issue is far more complicated that an expansion tank.

BackWoods is working with the person who sold him the boat to address the matter with the engine builder.

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Deano
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Re: Overheating problem. Any help would be appreciated!

Postby Deano » Tue Jan 17, 2017 7:32 pm

That was spam, not a real first post. (the quote has embedded spam)

You can tell Scotty is not back yet and Rick is busy, or that would've been gone.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

SWAMPHUNTER45
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Re: Overheating problem. Any help would be appreciated!

Postby SWAMPHUNTER45 » Tue Jan 17, 2017 8:17 pm

Gotcha !

Probably Russia now they have hacked Southern Airboat....where is ole Bud?


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