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Discussion Starter #1
This is the school O'day 35 with an Universal engine.

Their is no overflow tube or expansion tank.

Actually their is a tube but it is capped off.

Even if the engine has been off for a couple days if you crack the radiator cap, anti-freeze starts bubbling out.

I've never seen that happen before. What does it mean?

The anti-freeze that bubbles out looks OK, greenish.
 

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It indicates you have a nice tight leak-free coolant system. And that it is plenty full.

I'm not so sure it is a good idea to cap off the overflow tube as that would disable the pressure relief feature of the cap, yes?

Excessive coolant pressure, and many bubbles while running can indicate a head gasket problem. Or, very rarely, a crack in the block or head.
 

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Which cap are you cracking off? The one on the exhaust manifold, or the one on the header tank? It's normal for coolant to flow out of the cap on the exhaust manifold if you crack it, as the header tank is located well above that. Indeed, that is part of the bleeding procedure.

At least, that's how my Universal is set up.
 

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Discussion Starter #4
This is the cap the coolant comes out of.

This is a different boat because as you can see their is an overflow tube but other wise the setup is about the same.
 

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Discussion Starter #5
Which cap are you cracking off? The one on the exhaust manifold, or the one on the header tank? It's normal for coolant to flow out of the cap on the exhaust manifold if you crack it, as the header tank is located well above that. Indeed, that is part of the bleeding procedure.

At least, that's how my Universal is set up.
Not sure what you mean by header tank. If you are talking about one of those plastic expansion tanks we don't have one.

The overflow tube is capped off.
 

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OK, that is the cap on top of the exhaust manifold. Somewhere else, there will be a header tank. On my boat it is a grey metal tank, located high up in the top of the starboard lazarette. Look for it.
 

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My old universal m18 had no coolant recovery tank. Just make sure the coolant in the exhaust manifold is topped off to within an inch. The hose should not be capped off. It is a pressure release if the pressure gets too high. It should not leak though unless your cap is broken.
 

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You're talking about a coolant recovery tank, which catches coolant that passes through the pressure cap if it releases. What I'm talking about is a header / expansion tank, which is in the cooling system and is pressurised. It has a second pressure cap on it. It should be the highest point in the system.

If you have a header tank, the pressure cap on it should release at a lower pressure than the one on the exhaust manifold, which is thus not functioning as a pressure cap. It's just a plug.

You can of course have a coolant recovery tank, AND a header tank, which is what I have. The coolant recovery tank is connected to the cap on the header tank, NOT the exhaust manifold one.

You need a coolant recovery and an expansion tank to minimise the air in the system, if you are going to use modern long-life coolants. They hate being exposed to hot oxygen and then begin to crystallise. If you don't have either, better stick to the old 2-year green coolant.

However, the OP asked why coolant gushes out of the cap on the exhaust manifold. Answer : because there is a header tank he hasn't found yet.

"The overflow tube is capped off" : Because it's doing nothing, because the overflow tube that actually works is connected to the header tank.
 

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why coolant gushes out of the cap on the exhaust manifold. Answer : because there is a header tank he hasn't found yet.
I had exactly the same problem AND a header tank (that I didn't know was a header tank, and was baffled by) right up in the lazarette. This sure will make my engine checklist a lot less messy! Better check the level in the header tank...

Wow, that really should have been obvious. Now I'm having a "doh!" moment that just won't go away.
 

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Back in the day, the converted car engine's cooling system included a big plastic pop bottle with the bottom cut off.This was tied ,bottom upwith twine to the aft wheel house bulkhead At a glance you knew the situation re expansion,temp,and fluid level.What's more ,you had a real understanding of the systems that allows your equipment to be happy
 

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I have the same engine on a Catalina 36. It does not use a header tank. There is an overflow hose from the radiator cap that just goes to the bilge. Your system may be designed such that you do not need the header tank. If you open the cap like the one you have shown when the engine is still hot, you will get bubbles. When the engine is cold you should see coolant level at about and inch or more below the hole opening for the cap. Do you have a temperature gauge? If your engine is running at about 180 degrees or lower, you should be OK.
 

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Is there a water heater connected to the system? If the heater is higher than the engine, and in most boats it would have to be, that would cause coolant to flow out the cap as well. I still agree with the header tank idea though. Follow the hoses down and you should find it.
 

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Discussion Starter #13
You all were exactly right. I found another tank right next to the hot water heater with a pressure cap and an overflow hose.

It makes a lot more sense now.

Last question, well maybe not.

Is that header tank supposed to be full of coolant. It was about 4 inches deep and only had a inch or two in the bottom. I added another inch but didn't fill it.
Should I?
 

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If there isn't an atmospheric catch tank, the header tank is allowing for the expansion of the coolant, so it needs an air space at the top. I'd say about half way up is about right, when the engine is cold.
 

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Discussion Starter #16
Thanks you all. Makes sense.
 

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Discussion Starter #18

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I found another tank right next to the hot water heater with a pressure cap and an overflow hose.
I may be reading that wrong, but normally the pressure cap would NOT be on the expansion tank, but on the engine or water heater tank. The higher one I would think. Expansion tanks usually have just a silly splash prevention cap.
 

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I may be reading that wrong, but normally the pressure cap would NOT be on the expansion tank, but on the engine or water heater tank. The higher one I would think. Expansion tanks usually have just a silly splash prevention cap.
Try to pay attention. Read post 8. You are referring to an atmospheric catch tank, not an expansion tank.
 
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