3.0 exhaust manifold over heats

I have a engine with the cooling system as in the picture.
A new exhaust manifold is installed, new impeller and new thermostat.
The engine it self is not running hot, only exhaust manifold getting to hot. I guess that affects carburetor and intake of gas/air, cause after running full throttle for a minute of two engine dies.
Have tried without thermostat but didn't help. I have a good flow of water from the raw water pump.
Is it possible that there could be something wrong between manifold and elbow that restricts water flow?

Marine engines have constant water flowing to the exhaust manifold.

Verify you have good water flow

Scott Danforth said:

Marine engines have constant water flowing to the exhaust manifold.

Verify you have good water flow

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Yes that oss what I like to have. But if you look at the picture, there will only be a flow through the manifold when the thermostat is open. The constant flow that come from the bypass in the thermostat house connects after the elbow.
I think its a strange system. Would like to switch the hoses from thermostat house, but the are different sizes. Guess I can solve that part if needed. If I do that modification I get cold water from the impeller pump through manifold all the time, and warm water from open thermostat to go out after the elbow.

While I am not familiar with these engines and their water flow, I will try to help. After looking at online pictures of this engine’s components, I agree that water only flows into the intake / exhaust combination manifold when the thermostat is open. However, there is constant water flow to the riser via the bypass as you pointed out.

I suspect the cooling effect of the fuel / air mixture passing thru the intake side of the combination manifold provides sufficient cooling to the unit until everything starts to warm up > then the thermostat opens and provides additional cooling to the manifold.

As to your issue of the manifold getting too hot and causing the engine to shut down:

• From reading your original post it seems as if you are having the engine die when running at full throttle and you are attributing that to a hot manifold. Correct? If yes, then the real issue is the engine is dying at full throttle, correct?

Need some additional information.

• Is this a new to you boat? Is this a new issue and last year, no issues? Are you experiencing the engine dying at full throttle when the boat is in the water or on a hose (muffs)? Can you do a compression test and post the numbers? Any other maintenance done?

From this additional information we should be able to start to figure this out….

ESGWheel said:

While I am not familiar with these engines and their water flow, I will try to help. After looking at online pictures of this engine’s components, I agree that water only flows into the intake / exhaust combination manifold when the thermostat is open. However, there is constant water flow to the riser via the bypass as you pointed out.

I suspect the cooling effect of the fuel / air mixture passing thru the intake side of the combination manifold provides sufficient cooling to the unit until everything starts to warm up > then the thermostat opens and provides additional cooling to the manifold.

As to your issue of the manifold getting too hot and causing the engine to shut down:

• From reading your original post it seems as if you are having the engine die when running at full throttle and you are attributing that to a hot manifold. Correct? If yes, then the real issue is the engine is dying at full throttle, correct?

Need some additional information.

• Is this a new to you boat? Is this a new issue and last year, no issues? Are you experiencing the engine dying at full throttle when the boat is in the water or on a hose (muffs)? Can you do a compression test and post the numbers? Any other maintenance done?

From this additional information we should be able to start to figure this out….

Click to expand...

Thanks for trying to help me here.
One thing that I noticed in the Seloc maual is that on V6 and V8 the bypass from thermostat house goes through the manifold. Feeding them constant cold water from the lake. But not on the 4 cylinder, those engines just let the hot water from the engine cool the manifold. Guess it should work.

Manifold is getting so hot that the hoses lying on them is staring to melt. If I go full throttle I soon hear a sound similar to a really hot exhaust system on a car when you turn the engine of. (clicking sound) These tests has been done in the lake.

Boat is new to me, previous owner had changed the manifold and then the boat had been sitting for a few years.
I have replaced fuel pump, cleaned the carburetor and put in new spark plugs.

And the compression test, didn't turn out so great.
1. 11 bar
2. 7.5 bar
3. 6.0 bar
4. 10 bar

I did a valve adjustment, tightening the rocker arm screws until no gap and then half a turn. Manual say a full turn but I hear people say half a turn is better. On cylinder 3 I could just turn 1/8 of a turn or I loose all compression.
Could it be the hydraulic lifters that have gone bad?
And could this compressing issue cause manifold to over heat?

the cam could be toast.

do a leak-down test. that will tell you if the issue is valves, rings, head gasket, or washed out cam.

with the valve cover off, do all the rockers move the same amount (use a ruler or dial indicator)

Thanks for the background and further explanation. There are a few things going on here only one of which is hot exhaust. I do not think that low compression by itself would cause the exhaust to run excessively hot. But I do think if you have a situation where you are getting unburnt fuel into the exhaust it could burn off in the exhaust and cause it to get really hot.

Here is that hypothesis > you have a valve that seems to not be sealing completely in no. 3 and if it is the exhaust valve then some of the fuel/air mixture is escaping that cylinder unburnt and getting into the exhaust manifold where it does combust. This would be exacerbated if it is running rich.

Which valve on no. 3 was only 1/8 turn? And can you post pictures of the spark plugs?

Also, need to get the motor in a sound condition first > solve the issue of low compression. Follow what Scott outlines and post those results also.

Don't get off on a tangent. your problem is no water in the manifold. There is a plug on the bottom on the manifold, take that plug out and see if any water comes out. Check for blockage from the stat manifold to the exhaust manifold . it you run it long with no water coming out the exhaust it will melt a hole in the plastic coupler from the water pump in the outdrive pumping water to the engine. that plastic coupler is in the exhaust stream and depends on water exiting the manifold to keep it cool. the water has to travel from the exhaust manifold through ports in the riser where it sits on the 4 bolt flange at the back of the exhaust manifold, those ports have to be clean too. I have had this problem too with a 2004 3.0 and changed the manifold, the riser, and the check valve (flapper) at the exit of the hose connected to the riser.

Volvos do not use a flapper in the y pipe. There's is external on the back of the outdrive

charliedaubitz1 said:

Don't get off on a tangent.

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In reading thru the OP’s post and doing my own research both the OP and I are under the impression that, by design, there is no water flowing in the combination manifold until the t-stat opens (perhaps a tiny bit due to a weep hole). Certainly not the norm that we are all use to, but unless someone with this particular motor experience steps in and highlights otherwise or baring other info, I have no other explanation for the extreme heat of the manifold.

All my experience is on a mercury outdrive, not a Volvo. 3.0 is similar, I noticed a few differences in the water routing and I know there are differences in the impeller placement. I failed to notice this was under the Volvo section.

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I did a leak down test today, and the result was everything but good.
Cylinder 1 leak about 10% through valve control (seal).
Cylinder 2 leaks to cylinder 3.
Cylinder 3 leaks to cylinder 2 and through valve control (Seal) and a some through the carb. Picture of this measurement.
Cylinder 4 leaks about 30% through valve control
I guess this has to be corrected first, and then I can deal with the cooling issue. What do you think, a new head gasket and valve seal?

This is what the plugs look like, two middle ones are a bit white.
The elbow looks good to me. And I can not see that I have a check valve (flapper). Or could the whats left of it be stuck in the out drive, have to take it of to see that.

Ricky,
I am just reading thru your leak down post. Agree that best to get a sound motor first > fix the compression issues.

ESGWheel said:

Ricky,
I am just reading thru your leak down post. Agree that best to get a sound motor first > fix the compression issues.

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Yes that is the plan, one problem at a time. And maybe the leak in the engine can have something to do with the over heating? I'll get back here when I have some news.