Chevy 350 Engine coolant

Hi all
As im sure some of you will have offered advice to my questions regarding the rebuild of my Chevrolet 350 inboard
My question this time is in regards to engine temperature
The block is a 1969 5.7
What should my engine water temperature be running at ? ?
I've read a few posts on the Internet and as normal with this type of question there are a heap of conflicting answers
The trip before last the engine ran all day at 200 degress this being the first trip after a full rebuild but the last trip out it ran at 230
The coolant that in it is just green stuff from the local auto parts store and now I'm thinking maybe I need a specific coolant?
One comment I read was as long as the coolant doesn't boil the engine is not running to hot
Any advice would be greatly appreciate
Thanks Mike

 

The mercruiser manual shows a 160 F thermostat temp. So 200 or 230 is too hot
You do not need a specific coolant unless you have an aluminum block and heads and in 69 they were not common.

 

Yep, the coolant should be about 160. We already know it's an iron block. If you're running 200+, you have a problem, which could be anything from the pump, to cavitation, hot spots, as simple as "burping" out any air bubbles in the system, to restricted passages, to . . .

You should have a 160 thermostat and a standard volume pump, with regular antifreeze. There were no 4" bore, 350 blocks built by GM in aluminum, in '69. In fact, 1969 was the first year the 350 was available across the full Chevy lineup.

 

Hi guys,
When I went to the auto parts store with the original thermostat to get a new one during the rebuild the bloke convinced me the original was wrong and sold me a different one.
I can't recall what came out or what I put back in.
To be sure I've just ordered a 160 and I'll put it in.
If the currently installed one is wrong would this cause the engine to run hot like it is??
Thanks
Mike

 

If it is a 5.7 the block has to be from at least the 80's. The Gen II engines have different heads with reverse flow cooling. Check the casting numbers to verify which block and heads you have.

 

If you install the 160 and find that the temp is still too hot, then the cooling system that you have in place is not large enough to dissipate the heat. A poor functioning impeller for the raw water, restrictions in the coolant lines and passages can cause problems

If you had a 190 ish thermostat it should have been fully open at 190, and the operating temp then is dictated by the effectiveness of the coolant system.

Is your system closed or open? If you have ever had a rubber impellor fail, there is a good chance that some of the pieces are somewhere in the system and cause restrictions with the result of overheating

 

Hi guys
Ok yes the rubber impeller did break so may have pieces in the system can you explain the difference between open and closed system please
My system has a heat exchanger and exits out the exhaust
I did remove the round plates either end of the exchanger to replace the gaskets and no bits of the impeller where in there

Also how can I tell if the system has air bubble blockage

Thanks again
Mike

 

Ha guy's
Here's a picture

 

https://www.perfprotech.com/blog/articles/fresh-water-cooling-trouble-shooting

This is a pretty good article
When your impeller broke, I assume that you had the heat exchanger on so that any impeller parts would have been lodged in the heat exchanger?
Ie no parts in the engine

Send more pictures, from the top and both sides if possible

The raw water enters the heat exchanger, then heads towards the exhaust
There are a couple of options as it leaves the exchanger and I can not see how yours is plumbed. There are two parts to the exhaust, the exhaust manifold and the riser

Option 1 Raw water enters into the exhaust manifold at its lowest point, so that it floods the manifold, and then heads to the riser to be mixed with the exhaust gas to cool the exhaust

Option 2, The exhaust manifold is part of the freshwater part of your system, ie antifreeze runs through it. In this case the riser and the exhaust manifold is separated by a blocked gasket between the riser and the manifold. The raw water then only enters the riser to cool the exhaust.
Jet boats often have this set up as the raw water will often contain higher amounts of sand and every time you shut down, sand can have the chance to settle in the lower levels of the exhaust manifold and eventually plug it up

Did you modify the heat exchanger in any way? Ie braze on extra outlets?

An open system is one that does not have a heat exchanger and a closed is called FWC fresh water cooled.

The one that I commented on regarding a jet is a half system, half open or half closed, ( depending if you are an optimist or a pessimist) where the exhaust manifolds are cooled by freshwater/ engine coolant water.

So long as the raw water and the fresh water is flooding the exchanger from the bottom, there should be little chance of an air blockage.

On your exhaust manifolds, if they are raw water cooled, the water inlet should be at the bottom and flood the manifold then the flow moves from the top to the riser

The coolant side should enter the heat exchanger from the bottom, then flood the heat exchanger tubes and exit the top. This ensures that the fresh water has a change to completely cool. It is hard to see from your picture

One focal point in the article is that if you have a 160 degree thermostat the actual engine temp might turn out to be 180 at the sensor. So if you had a 180 or even higher thermostat, your engine could easily reach 200 plus. 230 is very hot though

 

That fuel filter is not for inboard installation. They are usually used on outboards and installed in the stern well. That is, assuming it is a gas filter and not a diesel.

 

Hi All,

Here are some additional photos
the risers fitted to the motor in photos have now been replace with new stainless steel set as in photo.
If bits of impeller rubber are lodged in the cooling system where is the most likely place they would be ?
The impeller broke on the first start up with the motor reinstalled due to sitting for 2 years, i was amazed when i pulled the impeller to find all the paddlers gone and only the rubber shaft left, i would never have believe it could be completely destroyed.

I am hoping that replacing the water thermostat with a 160 will fix the high water temperature but ive learnt with this rebuilding stuff nothing is easy LOL.

Thanks,
Mike

 

If there is a power steering cooler, that is another spot where the impeller blades get stuck.

 

Hi Gonzo,

Yes it has a steering cooler so i will check that.

Thanks,
Mike

 

That's not a gen II 350, but in fact a 1969 350, I ran the numbers myself a month ago.

Cooling systems can cause some baffling to some, but they're pretty basic. They need to be clean and free of debris, filled so no air pockets form, appropriate parts (impellers, thermostats, etc.). You may also want to check the condition of the exchanger. Pull the end cover and see what it looks like. The clog and corrode pretty easily, but they can be "boiled" out at a radiator shop.

 

It is difficult to see the water flow in the pictures as I cannot see the raw water pump

So in a nutshell,
From the raw water pump, the flow can go through an oil/power steering cooler and from their must go to the heat exchanger, from the bottom if the heat exchanger has a bottom inlet, so the entire exchanger floods, then from there directly to a T which sends the water to the bottom of the exhaust manifolds. It appears that you have one piece exhaust manifolds and risers.

The other loop should be from the top of the heat exchanger into the engine, again so the exchanger completely floods, to the circ pump then back to the bottom of the heat exchanger.

Because the pictures do not reveal some of the hoses, it might be worth taking the boat to a dealer who has experience in this to follow the water flow. Might save you some hassle and an engine

re your question as to where the rubber vanes might be. IF you had the exchanger in place, then on a FWC system, most of the pieces will be in the inlet of the exchanger.