1999 5.0L MerCruiser Exhaust Manifold Temperature Question

[Juno]

Hi guys, I put my new to me boat in the water this weekend for the first time this year. I took it out for a short run had it running for about 45mins at various speeds. When I get back to the dock I open the engine compartment to check everything out and I noticed that;

looking from the front of the engine towards the back of the boat, the LEFT exhaust elbow essembly was warm to hot to the touch, not hot enough to burn anything and the RIGHT side was cool/cold. I just placed my hand on the top of the elbow.

Next time out I will bring my infrared temp gun to check the actual temps, but I was just wondering is this normal for one to be hot and the other cold? My first 8 cylinder engine, I have always had a 4 cylinder with 1 exhaust mani and elbow.

Would this indicate a problem that I should investigate further?

Thanks everyone

 

[alldodge]

Re: 1999 5.0L MerCruiser Exhaust Manifold Temperature Question

The exhaust risers would be warm but not hot. Having one hotter then the other would be something to look into. Check the hose and fitting leading to and the manifold and thermostate housing and see if you have a restriction.

 

[Juno]

Re: 1999 5.0L MerCruiser Exhaust Manifold Temperature Question

The exhaust risers would be warm but not hot. Having one hotter then the other would be something to look into. Check the hose and fitting leading to and the manifold and thermostate housing and see if you have a restriction.

Thanks for the quick response. I will pull of the hoses going to the left side to look for any obstructions.

Does anyone know of an acceptable temperature rage for the exhaust manifolds for the 5.0L?

Regards,

 

[ryno1234]

I realize this was 9 years ago, but do you recall what you found when investigating this?

 

[Lou C]

One will always be a bit warmer than the other, for one thing the water flow to each side is never 100% equal and another it depends on how the boat sits on the trailer or in the water, if one side is lower that gets more water so it will run cooler. Mine sits lower on port side on the trailer so starboard is a bit hotter at idle on the trailer. In the water, more equal, they are close to the same but not equal.
Mercruiser, you have to go by if you have warm manifolds or cool. Warm manifold system has two connections, the elbows are fed by the stat housing all the time but the manifolds don't get water flow till the stat opens and even then that water is much hotter because it just came out of the engine. So those warm manifolds will run much hotter, like about the engine temp, or even somewhat above. So with that system I would not be surprised to see manifolds at 150-175 or so, but the elbows should be cooler, like 100-130, at idle.
If you have cool manifolds (only one water connection first feeding the manifold then the elbow) they will run much cooler, like 95-110 at idle, and 120-135 after coming off plane. My set up (OMC/Volvo) is cool manifolds and that's what they run at.

The idea behind the warm manifolds is to eliminate condensation in the manifolds when running at low speed for a period of time, which is a good idea actually.