350 Chev, do I run with or without Thermostat?

[Vobby78]

Hi all,

Just after some mechanical knowledge about whether or not to run a thermostat in a
350 Chev inboard. The motor is in a Pride 22 sunseeker which I recently purchased, beautiful boat!

Anyway, I am replacing afew things on the motor and I checked under the thermostat housing to find a thermostat with its guts ripped out, so in actual fact there is no thermostat.

The motor is cooled using an aftermarket heat exchanger, which as far as i know does a great job. I've been told that you can run it flat chat for around 40 minutes before you need to throttle off a little to cool the motor.

Sshould I replace the gutted thermostat with a new fully functioning one, or are they generally not required?

[sportfish58]

G,day,

You should always have a working thermostat in your engines.
They do a few things ,control water temp and water flow,they also stop hot and cold spots in the engine which can decress engine life.
Its best to have the engine run at a constant temp.
If you have temp issues with a working thermostat you may need to check the heat exchange unit or pump.

Cheers

[BM]

You should be able to run flat out more or less indefinitely. The removal of the thermostat suggests the prior owner was trying to resolve an overheating issue.

As mentioned the thermostat should always be fitted. The engine is designed to operate with one.

I'd be looking at whether the heat exchanger is too small or whether you have restriction in your exhaust elbows. Also make sure your water pump is in good condition.

For an overall pic of the engine or the heat exchanger?

Cheers

Edit: I hadn't seen the pic before posting. That's an unusual looking setup. Those stainless manifolds are manifold and elbow in one piece so how are you recirculating the coolant? Typical freshwater cooling systems cool the engine and manifolds via coolant and the manifold to elbow interface is blanked off thus leaving only the exhaust elbows that have salt water passing through them.

So I gather in your system that the engine block is running coolant and the stainless manifolds are running seawater? Very strange setup and probably why there are some issues with the setup.

[Chimo]

Why not stick your exhausts straight out thru the transom and get a nicer note, an extra 30 or 40 HP due to a lot less back pressure and maybe cool the engine a bit too. I also wondered if the heat exchanger was up to it?

How are the Hi Teks going, how old are they? Just fitted a pair to a friends 350. His motor temp sits at 175 but it is raw water cooled in a 28 Bayliner with exhausts thru the leg too and his boat could really benefit from some extra HP when getting onto the plane so straight thru the transom may happen.

Cheers
Chimo

[BM]

Chimo, thru transom exhaust sounds great when it's someone else's boat going past..... When your in one for a period of time the drone drives you nuts.

[Chimo]

We used to feed a bit more water in to quieten them down; 80dba at 100 ft for ski racing!

Also if you go faster into the wind its soooo good.

C
C

[Jarrah Jack]

We used to feed a bit more water in to quieten them down; 80dba at 100 ft for ski racing!

Also if you go faster into the wind its soooo good.

C
C

Says the hoon from Horsham..

[cormorant]

Where is the rest of the thermostat. Never underestimate the ability of someone to pull somehing apart and then put it back together knowing there is a problem!

[OPTI]

it should have a thermostat as mentioned ,im also concerned at the automotive alternater and msd dizzy,check that these are shielded as per marine specs,very big risk factor of explosion running those.

[Gon Fishun]

A big lot of years back we would remove the thermostat, gut it and put it back in. We found if the body wasn't in there the water flowed to quickly and didn't get a chance to cool through the radiator. I doubt if this has anything to do with your problem, just thought I'd chuck it in there.

[Craigo]

If you do run without a thermostat, just cut the working centre bit out, the centre hole provides a bit of restriction to keep the water flow in check. A Thermostat just gets the motor to operating temp quicker and provides a controled restriction

[Stuart]

It also keeps the engine at the correct operating temp to reduce wear. If an engine runs to hot, it wears, runs to cold and it wears even faster. Dont go cutting the centre of the thermo out either, you may as well not have it in. The 350 chevs normally run a 180 degree F thermostat same as the Ford 302 and 351s. You could drop the thermo down to 160 but if you have a look on line as to what thermostat to run then stick with that. I would say one od two resons why it wasnt in there was the old owner thought not having one in means it runs cooler so that must be better...Wrong. Second and as its been suggested perhaps there is an over heating issue. There is an Australia product called "watch dog digital heating alarm" that is worth its weight in gold. Problam with most heating gauges on the market is the sensore. They rely on water traveling over them to show the temp, if the water is gone it wont give a true reading.

[Vobby78]

Thanks guys for all your feedback. The heat exchanger is cooling the engine and the risers (no seawater). I reckon I will need to change the heat exchanger, its an aftermarket brassy looking thing that has been put together by previous owner, granted they have done a good job, I just dont think they chose the right hex. Will try and find a hex setup to suit a 5.7l mercruiser I suppose!

[Vobby78]

Hi Bud, thanks for your concern. These MSD dizzies are made for Boats, im sure they are shielded as per marine specs, as for the alternator, not too sure, I will have a looks tomorrow.

[Mr__Bean]

Why does the engine coolant also run through the stainless exhaust elbows? At that point you are dealing with raw flame out of the engine exhaust, that seems like hard work for the coolant.

If the elbows are stainless steel, why not run the heat exchanger raw water back through the exhaust elbows on the way out, thus reducing how much heat transfers into the coolant?

Darren