Very interesting find about overheating engine

[calincoltsdad]

My 4.3 V6 yamaha was overheating when I found there was no thermostat in the engine. I put a 160 in it but the temp. was still going up to 180-185. Service center said it should have a 140 therm. in it. Ordered a 140 but haven't got it yet. I found that if you open the petcocks on the exhaust manifolds while its running the engine doesn't run hot. Why is that? Is the water going in the exhaust manifolds only there to warm the engine since it bypasses after it comes to operating temp through the risers? Would it hurt to run hoses from the petcocks to the rises and Tee in and run the engine? Also I have more water flow from the drivers side manifold than the other side. Could there be an obstruction?

 

[Don S]

Re: Very interesting find about overheating engine

You may have clogged exhaust riseres. When they clog up, the water can not flow through the engine and out the exhaust as designed. When you opened the petcocks, the water circulated and cooled the engine.
Time to inspect the manifolds and riser.

 

[calincoltsdad]

Re: Very interesting find about overheating engine

So should I just take off the risers and look there first. Will have I need to look for anything specific doing so? The risers stayed hot while there was no thermostat in the engine but when I put one in they would be cool when it opened. Warm to the touch but you could hold your hand on them. When the engine got hot there was steam coming from the vicinity of the risers so that could possibly be the problem, right?

 

[JustJason]

Re: Very interesting find about overheating engine

Yep just pull the risers on both sides. You will see cooling passages in the manifold and in the riser, and what you are looking for is to see how clogged they are. Unless they are brand new they all have a little bit of surface rust in them, but you are looking for heavy scaling/clogs.

Btw... you'd be doing yourself a favor if you dumped that boat on somebody else... Yamaha is not supported (and hasn't been for a while) here in the states. Parts and service are EXTREMELY hard and EXPENSIVE!!! to come by.

Good luck!

 

[calincoltsdad]

Re: Very interesting find about overheating engine

Even though its yamaha its a standard chevy 4.3, right? Can you not use risers off a merc 4.3? Also how do you know when to replace them? Its a 92 so they have some age on them. Would it help if I knocked out any scaling thats in them? If the risers were clogged would the hoses connected to them get hot, they stay fairly cool when running. Since opening the petcock on the manifolds cools the engine down would it hurt to run it with those open and hoses connected to them and tee into a discharge line?

 

[JustJason]

Re: Very interesting find about overheating engine

The engine is a GM. But it's everything else besides the engine that nickle and dimes you to death. But the bigger problem is Yamaha parts don't nickle and dime you... they hundred and thousand you, and it adds up quick.

As far as opening the petcocks... Mickey Mouse it any way you want... But that is not the way the system is designed. Cooling water NEEDS to come out of the exhaust manifolds. You can hurt other parts, down the line after the manifolds, if there is no water in there. So yes it would hurt to run it that way.

Only thing you can really do is pull the risers and to a manual inspection... that's the way we do it in the shops.

 

[Don S]

Re: Very interesting find about overheating engine

Can you not use risers off a merc 4.3?

Can you use Toyoto parts to fix your Chevy engine?

Get real. They are two completely different companies. Like Merc and Volvo, Omc and Merc.
The long blocks of the engines are the same, everything else is different.

 

[JustJason]

Re: Very interesting find about overheating engine

I had a Toyoto once.... A Toyoto Supar

 

[dan t.]

Re: Very interesting find about overheating engine

actualy chev and toyota mix quite well, I had a land cruiser with a 350 v8 in it, as for manifolds and risers, you could use merc or volvo, just be prepared to do some fooling around to mate up the exhaust Y pipe

 

[dan t.]

Re: Very interesting find about overheating engine

to amend my last reply before some hair splitter jumps on it, the manifold and riser must be matched.

 

[calincoltsdad]

Re: Very interesting find about overheating engine

Thanks for the replies. I'll try to start pulling the risers off today and see if anything is in them. This boating thing is new to me so I'm learning a little bit at a time. Didn't realize there were so many different parts and brands.

 

[calincoltsdad]

Re: Very interesting find about overheating engine

Ihave very little water coming from the passenger side exhaust manifold petcock valve. The drivers side has alot of pressure. Should I check that side first for obstructions? How can I check the circulatory pump correctly to see if it has the right amount of output?

 

[calincoltsdad]

Re: Very interesting find about overheating engine

Also when i have the muffs on the boat little water comes out the prop, some comes out of the holes under the cavi. plate and alot comes out of the bottom of the boat right under the plug. Is that right for the exhaust to come out of that area?

 

[calincoltsdad]

Re: Very interesting find about overheating engine

Took the right side riser off and everything looks good. It looks to me that the water runs to the risers and down the manifolds and back into the intake. Then mixes with fresh water and out the top outlets on the risers. What could be causing the overheating problem?

 

[P 0 P E Y E]

Re: Very interesting find about overheating engine

I take it the engine is fresh water cooled.

That means you have two cooling systems

a raw water and a fresh water one.

The rust and clogging will happen in the risers or mixing elbows. Inspect there.

You could also remove the water hose at the manifold and blow into the hose and see if it is restricted.

If you cant get the right thermostat, cut the middle part out and put the restrict plate back in and run some more tests.

Pressure test the system, bleed the system, grab the circ pump and see if the pulley wiggles. See if the belt is tight

Good luck and keep checking till you find the problem.

 

[calincoltsdad]

Re: Very interesting find about overheating engine

All hoses are clear. Water pumps are ok and have plenty of flow. Why when I open the exhaust petcocks the temp stays down? I can't understand why water comes from the bottom of the exhaust manifolds and then dumps into the intake. That doesn't make sense to me. That would make the engine stay hot all the time. I have a 160 therm. now and it still runs up to 175 at the housing. I have ordered a 140 but even without one the engine would overheat until I opened the petcocks. Risers and exhaust manifolds look good. Only surface rust no flaking or obstructions.

 

[JustJason]

Re: Very interesting find about overheating engine

pull those petcocks right out. After you think you have all the water out of them, stick a small screwdriver up those holes to break up any rust that may be covering the hole. You'll see how much rust comes out, belive me.

At this point i'd pull the risers anyways. Take a pic or 2 and post it here.

 

[calincoltsdad]

Re: Very interesting find about overheating engine

I have plenty of flow from the petcocoks, no rust in them. Risers look good. Why would the engine run cooler with the petcocks open?

 

[mkast]

Re: Very interesting find about overheating engine

Because water is moving. Do yourself a favor, download the maintenance manual, study the cooling system, then you'll know.

 

[JustJason]

Re: Very interesting find about overheating engine

How do the discharge ports of the risers look... where they fit into the rubber boot. They often get clogged there.