INBOARD marine 350 Chevy running too cool!

[LAWRENCE Owen]

Subject: my fresh marine Chevy 350/375hp in the 1977 Aquasport 222 Osprey. Raw water cooled engine is running great, but temps are in the 110° to 130° and it takes forever to warm up. 140° thermostat. It will get up to 140 on the gauge at, say, 4000 rpms, but in my mind not fast enough. I think I should be reaching at least 160°, even 180° (?).

Do I need a circulation pump? Or some restriction in the current system? I pulled the engine to fabricate some new brackets for the water pump and the alternator so they align correctly. Now's the time to make adjustments on the cooling system.

You guys are always so helpful. If you could analyze this using my limited info please do. Larry

 

[achris]

Larry, Larry, Larry. Where do I start?

Non-marine carb and flame arrestor (it's not even a flame arrestor, it's just an air filter ), non-marine distributor, non-marine fuel pump. I suspect that starter motor's also not marine... There are extremely good reasons for SAE-J1171 and SAE-J1223... And no it's not JUST to make money, it's to stop boat's like yours from exploding! That engine is literally, a bomb ticking!

As for the cooling system, if you can use the word 'system' for that, I'm not surprised the gauge isn't reading much, and it takes an age for the gauge to sense. There is no water flow (none at all!) until the thermostat opens, and while the gauge is showing a 'low' temp, I'm pretty sure the rear cylinders will be baking in the heat!

Below is what the system SHOULD look like...

Chris...........

 

[LAWRENCE Owen]

Hello, Chris! Your input is SO very much valued, and I'm positive that 98% of your advice and observations are spot on, but this situation is falling into the 2% range. The Holley-made carb is marine with the correct Holley marine carb return tubes, it is an expensive all-metal flame arrestor that was on the original factory Crusader 350 engine (I painted it gold and red), the DUI Distributor is the marine version, and the starter is a marine-specific one, shimmed to mate with the Gen I Chevy engine. The fuel pump is a Jabsco marine pump for this engine. Everything on the engine is marine grade. It's a rebuilt marine 350 5.7l engine, with an Edlebrock marine intake manifold.

I use a laser heat gun to track the temps at every point on the engine; thermostat housing, hoses, block, manifolds, risers and exhaust water. At no point do the temps indicate more than 125° when warmed up. The engine is running quite well, but I fear the low temps are causing the oil temps to not be ideal, and it's costing me horsepower, based on my experience with my drag and track cars and motorcycles. Please forgive my defensive posture, but I'm an 80-year old codger who has a propensity to blabber on and on!

 

[achris]

Ok, I'll take that.... (Never been a fan of Holley carbs, marine or otherwise, but that's another story)... Let's look at the plumbing of the cooling system....

Correct me if I'm wrong....

Water is pulled in by front pulley driven sea-water pump, which has a 2-way outlet. One going to each exhaust manifold. I'm going to assume the manifold/elbow gasket is a block-off, as if it wasn't that engine would overheat quick smart...

Water exits the exhaust manifold (at the top) and then passes via a hose to the front of the engine block, passes through the block and heads and then gets blocked against the thermostat if it's not open, or flows out the thermostat if it is open, through the elbows and out...

How close am I?

So, what problems do we have here? First up, you want the COLDEST water to be headed for the engine FIRST, not the exhaust manifolds, which under full load will heat that water up to the point for it being not so good for cooling the engine.

Second, when the thermostat is closed, the sea-water pump is deadheaded. Bad idea. Also, no water flowing out the elbows, so they're going to get way too hot, as will the entire exhaust system. Fire risk right there. Also with the thermostat closed, none of the warmed water will come in contact with it to signal it that the engine is at operating temp and it needs to open. I can't see where your engine temp sensor is located, but I suspect the reason why you're not seeing much on the gauge is because there's no water flow within the block/heads before the thermostat opens.

That thermostat housing isn't even remotely right for a marine setup. It's literally just a thermostat cover. Have a look at the water flow diagram I posted earlier, see that it allows for a)water to flow around the engine while it's warming up, and b) for water coming from the sea-water pump, that's not being allowed to enter the engine as it's not warm enough yet, to flow out of the housing and through to the elbows. That ensures that the exhaust gasses are being cooled all the time, not just when the thermostat is open.

You need to completely redesign that cooling system to avoid a fire caused by the exhaust system running at time with no water, and to allow the water in the block to be continuously circulating. The pump that's not on the front of your engine is called a 'circulating pump'.... And you need to get the cooling water into the engine first, not last.

Chris..........

 

[achris]

I've also combined your PDFs so it's easier for anyone else to open it up and look at all the photos in the same file....

Chris.....

 

[LAWRENCE Owen]

Ok, I'll take that.... (Never been a fan of Holley carbs, marine or otherwise, but that's another story)... Let's look at the plumbing of the cooling system....

Correct me if I'm wrong....

Water is pulled in by front pulley driven sea-water pump, which has a 2-way outlet. One going to each exhaust manifold. I'm going to assume the manifold/elbow gasket is a block-off, as if it wasn't that engine would overheat quick smart...

Water exits the exhaust manifold (at the top) and then passes via a hose to the front of the engine block, passes through the block and heads and then gets blocked against the thermostat if it's not open, or flows out the thermostat if it is open, through the elbows and out...

How close am I?

So, what problems do we have here? First up, you want the COLDEST water to be headed for the engine FIRST, not the exhaust manifolds, which under full load will heat that water up to the point for it being not so good for cooling the engine.

Second, when the thermostat is closed, the sea-water pump is deadheaded. Bad idea. Also, no water flowing out the elbows, so they're going to get way too hot, as will the entire exhaust system. Fire risk right there. Also with the thermostat closed, none of the warmed water will come in contact with it to signal it that the engine is at operating temp and it needs to open. I can't see where your engine temp sensor is located, but I suspect the reason why you're not seeing much on the gauge is because there's no water flow within the block/heads before the thermostat opens.

That thermostat housing isn't even remotely right for a marine setup. It's literally just a thermostat cover. Have a look at the water flow diagram I posted earlier, see that it allows for a)water to flow around the engine while it's warming up, and b) for water coming from the sea-water pump, that's not being allowed to enter the engine as it's not warm enough yet, to flow out of the housing and through to the elbows. That ensures that the exhaust gasses are being cooled all the time, not just when the thermostat is open.

You need to completely redesign that cooling system to avoid a fire caused by the exhaust system running at time with no water, and to allow the water in the block to be continuously circulating. The pump that's not on the front of your engine is called a 'circulating pump'.... And you need to get the cooling water into the engine first, not last.

Chris..........

Chris, you're the best. I forwarded your letter to the seasoned mechanic who's helping me straighten this out (a 45-year friend). He fully agrees with you. He had showed me the same diagram you attached and he concluded the current setup might have been okay for the original Crusader engine but the current engine needs more elements. He suggested the circulating pump, and I'm researching what's available which will fit this engine. Chevy Gen l block with Vortec heads and roller cam. Purchased as a long-block. New Mercruiser manifolds and risers and all new hoses, most wiring, etc. If you or anyone can help me with identifying parts and methods we should know .... it will help immensely!

 

[achris]

You have 2 options. 'Warm' manifolds or 'cold' manifolds.

Warm manifolds hold the water in them until the thermostat opens.
Cold manifolds take the exhausted engine cooling water once the thermostat is open, but the unused excess (cold) incoming water when the thermostat is closed. Hence a greater variation of manifold temp.

Cold manifolds are easier to set up, but warm manifolds keep the manifold temperatures more even.

Parts required.
Regardless of which way you fly, you're going to need an engine circ pump. Any SBC marine pump will do. The difference between standard automotive and marine is that the marine has stainless steel seal and back plate, automotive have mild steel.

Water pump: Merc# 8M0119794.
Hose from water pump to T-stat housing: Merc# 32-861590A05

Now you need to choose, warm or cold? A warm manifold setup is going to need a 6 port thermostat housing, cold only requires a 4 port. In your situation, I'd probably opt for the warm. All the parts you require are available from Mercury (BTW, as much as I suggest Merc parts, I have serious issues with them, I am not their friend!). You should also look at Sierra and GLM to see if they do the same thing.

Thermostat housing: Merc# -16413A9 (with associated nuts, bolts, screws and gaskets.)

As for hoses, you can use the pre-formed Merc hoses, or just generic water hose, up to you.

You will also need the right manifold/elbow gaskets: I would use a block-off gasket, with a 3mm hole at the aft end (to allow for air purge)...

If you want cold manifolds, use a 4 port t-stat housing: Merc# -87290A4 and full flow elbow gaskets.

The distinction between elbow gaskets is very important!

Chris..........

 

[QBhoy]

agree with the above and think you’ve got a hold on things. But 140 sounds normal for a closed cooled system. Only thing that perked my brain…was around the idea of 375hp from a 350 carb marine engine. Sounds high to me perhaps

 

[achris]

agree with the above and think you’ve got a hold on things. But 140 sounds normal for a closed cooled system. Only thing that perked my brain…was around the idea of 375hp from a 350 carb marine engine. Sounds high to me perhaps

160 is closed cooling. 140 for sea water.

 

[QBhoy]

160 is closed cooling. 140 for sea water.

Think we might have disagreed about this not too long ago. Haha. Can’t remember the details. But as far as I know Chris, my current raw cooled is a 160 t stat for sure. Always thought all raw were 160 and closed were 140. But I’m aware that this may depend on where you are and fresh or salt water immersion perhaps. Not sure. What was the outcome of the last time we spoke about this. Can’t remember. But I’m certain I have a 160 in my raw mpi. So do a pair of VP 350 carbs I know of too. My mpi will run at 152-154 degrees normally but very cold fresh water. She won’t come close to 160 or more unless she’s up running into the 60’s for more than a minute or so

 

[achris]

Later engines use 160 for seawater cooled to reduce emissions, allegedly.

 

[achris]

Just been through a bunch of specs in as many manuals. It's all over the place. Some have both (closed and sea water cooled) specifying 140, some have both specifying at 160. Some even specify 160 if the t-stat is SS and 140 if it's brass. Looks like the only thing we can conclude is that either thermostat can be used in either cooling system.

I think the best advice is to use what the manual specifies.

 

[QBhoy]

Just been through a bunch of specs in as many manuals. It's all over the place. Some have both (closed and sea water cooled) specifying 140, some have both specifying at 160. Some even specify 160 if the t-stat is SS and 140 if it's brass. Looks like the only thing we can conclude is that either thermostat can be used in either cooling system.

I think the best advice is to use what the manual specifies.

Think that’s what i concluded too Chris. Defo all over the place. You’re right though. Looks like early raw water cooled look like they spec 160. Later I think 140.
On a side note. One thing I’ve been aware of recently…my mpi 5.0 runs about 152/153 99% of the time. But I know of at least 3 boats with same engine but with a bravo 3 that run 165ish give or take either way. All read from smart craft ecu data. Not gauges. Also noticed how much cooler my other boat runs. She has a 115 2016 merc. She runs in the 120’s at most.

 

[Bondo]

agree with the above and think you’ve got a hold on things. But 140 sounds normal for a closed cooled system. Only thing that perked my brain…was around the idea of 375hp from a 350 carb marine engine. Sounds high to me perhaps

Ayuh,..... I saw that too, 'n wonder just how big the cam is,.....

Especially considerin' Larry is an ole race car driver,.....