Mercruiser 470 thermostat location??

mudpuppy86

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I know I need a manual but I was wondering were the thermostat is located. I replaced the water pump and the motor still overheats when I crank it up. Antifreeze comes out the radiator cap but the temp gauge reads 145. I am new to the I/O boats. Any response whould be greatly appreciated.
Thanx,
George
 

Don S

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Re: Mercruiser 470 thermostat location??

"Which" water pump did you replace? The raw water pump in the drive, or the engine circulating pump (aka "Water pump" in the auto industry)

The thermostat (item 21) is between the coolant reservoir (item 23) and the thermostat housing (item 15)

470%20Tstat%20hsg..png
 

Don S

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Re: Mercruiser 470 thermostat location??

when I crank it up. Antifreeze comes out the radiator cap but the temp gauge reads 145.

It could also be that you don't have an overheat problem, but a blown head gasket or cracked head or block causing the combustion pressure to go into the cooling system and blowing the antifreeze out.
NAPA carries a kit for checking for exhaust in the cooling system. Might be worth checking before spending a lot of time looking for an overheat problem.
 

mudpuppy86

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Re: Mercruiser 470 thermostat location??

Outstanding, thanx for the advice on the head gasket idea, would not have thought of that. I replaced the water pump in the lower unit.
Thanx,
George
 

mudpuppy86

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Re: Mercruiser 470 thermostat location??

If I take the thermostat out to run it and see if that was the problem, would that work. I would do it just to see if that was the problem. And would the antifreeze comming out through the cap happen at low rpm also or only high rpm if it was the head gasket being bad?
Thanx,
George
 

Don S

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Re: Mercruiser 470 thermostat location??

You could try it for a quick "Off the water" test, but with the thermostat out, the front of the engine stays cold and the back gets hot because of the antifreeze circulating too fast. If you are going to all the problems to open it up, you need a new gasket anyway. Put in a new thermostat and check it.
Did you ever verify if it was actually overheating or just the fact that water was coming out the cap that it MUST be from overheating?
 

mudpuppy86

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Re: Mercruiser 470 thermostat location??

Not yet. The other thing I noticed was that I was getting some smoking around 2 to 3 spark plugs when the antifreeze was leaking out. The top of the motor and antifreeze was definatly hot also. I won't be able to do anything more till tomorrow. When I squeeze the bottom hose from the thermostat to the heat exchanger, I can here the antifreeze/air moving in the reservoir. Now I am leaning towards the head gasket.
Thanx,
George
 

Don S

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Re: Mercruiser 470 thermostat location??

I think you are reading too much into things happening that means little or nothing.
Smoke from antifreeze is normal around a spark plug and the exhaust manifold/head joint. It gets hot there and antifreeze steams when fried.
Second, hearing bubbles when you squeeze a hose doesn't mean anything.
You need to do some testing, not guessing.
A leakdown test on each cylinder with the cap off the reservoir will show a leak. You will see bubbles coming up thru the antifreeze.
There are Soooooo many things unknown about your problem that it's impossible to give you an absolute answer.
You need to get one of those non contact infared temp guns and check different places on the engine and manifold and see if you are actually getting an overheat, you need to do the leakdown or exhaust gas test I mentioned earlier.
You could have a plugged heat exchanger from old part of a deceased impeller, plugged exhaust riser, lots of things.
Sorry, no EZ, one fix fixes all, type fixes for your problem.
A Mercruiser service manual could walk you through all the steps needed to troubleshoot the problem.
Changing parts to find the problem is very expensive and usually doesn't work.
 

mudpuppy86

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Re: Mercruiser 470 thermostat location??

I understand, just was giving as much details as possible. The smoke around the spark plugs was not from antifreeze. It ran down the front of the motor and was not near the plugs. And the antifreeze was almost acting like it was foaming out of the cap. I will get a kit from NAPA on Monday.
Thanx for your help, it is greatly appreciated!,
George
 

mudpuppy86

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Re: Mercruiser 470 thermostat location??

I noticed after taking the exhaust elbow off that when I put my garden hose to the cooling connection at the end of the exhaust manifold were the elbow bolts on and fill it with water there that antifreeze comes out of a few pin holes in the manifold exhaust port just under were the elbow bolts on. Could this be enough were the exhaust and the antifreeze is meeting that it could be blowing antifreeze out the cap?
Thanx,
George
 

manderson1

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Re: Mercruiser 470 thermostat location??

Quick question...where is the thermostat on your 470
 

bruceb58

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Re: Mercruiser 470 thermostat location??

Instead of replying to a 3 year old thread, you should start a new one. You will get more responses.
 

manderson1

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Re: Mercruiser 470 thermostat location??

OK...thanks...I can appreciate that, but I was simply replying to a thread that was listed below as a similar thread...maybe they should just be discarded if they are this old and it is a dead issue.
 

CAPTKEV85

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Re: Mercruiser 470 thermostat location??

Well i had the same issue turns out my head was bad. every valve guide was cracked causing combustion air to get into coolant jackets. put new gasket and head on and she runs great.
 
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