470 Overheat

[aussie]

Originally Posted by dan4836

Dished pistons

that's strange mine were dished top but some of the other engines I seen on ebay were flat tops were the oversize and did you get it going

[dan4836]

I did get the boat going and we went for a test ride yesterday.

Motor ran great but i still get a large gap between temp readings. If I let the boat idle, the temp will read 120. If I cruise the boat at 3500 rpm, the temp will slowly get to 200. Back off the throttle to 1200 and the temp will drop down to 120.

I did not overheat but I did get coolant releasing into the overflow container.

My question - If I have a 160 degree thermostat, why a 80 degree sway in temp?

Items I changed so far:

1) Upgraded from 3" to 4" heat exchanger. Checked and cleaned exchanger.

2) Replaced the raw water pump three times. The last time replaced the housing as well.

3) Replaced the riser.

4) Removed the water cooled voltage regulator and ran a new hose from the transom to the heat exchanger

5) Removed the head, machined and re-installed

6) New thermostat

What else is left?

My only thoughts now are something in the flow of coolant on the fresh water side. Either the thermostat or the engine circulating pump. I installed the thermostat with the springs down ( I have the old stye 470) perhaps I have the incorrect thermostat?

Any thoughts?

[aussie]

It has to be water flow . raw water may not be flowing enough . Water pump on engine not pumping enough . Did you check the water pump impellor on the engine there is a cover on the timing cover check if the impellor is worn . I don't know how you are checking your leg pump most guys use the ear muffs on the legs and its not a good way to check your pump as its being feed under pressure when I have heating problem I run the leg in a drum so you get to see how well the pump is working

Find the hose that comes of your leg and connect a garden water hose to it and turn it on . Follow the route of the hoses and remove one hose at a time to see if something is restricting water ( example ; check water flow before manifold and after ) you need to eliminate everything that water goes through. If everything is flowing good then check your raw water pump . Put the leg in a drum leave the hose of the leg start the engine and see how much water the pump is pumping .If all is fine then its your water system on the engine

It can only be the water pump on your engine . you have done every thing else

Spares might be able to help you more as car mechanic hes a boat one

GOOD LUCK

[dan4836]

After looking closely at my thermostat and housing, I found the thermostat installed does not close off the circuit (engine side). I have the older style manifolds and the bottom part of the thermostat is smaller than the hole that allows the coolant to flow back through the engine.

In other words, when the thermostat is closed, no water can go to the heat exchanger. when the thermostat opens, on top the coolant can flow from the bottom and through the thermostat to complete the circuit to the heat exchanger. Also, when the thermostat opens, it should close off the circuit that goes back through the engine.

- The thermostat foot is too small and does not make it to the bottom to close of the hole.

My research shows that only two thermostats are made for the 470. One for my style manifold and the other for the aluminum manifold set up.

Any suggestions?

[aussie]

Take. The thermostat out and try it. Even with the thermostat not being rite once it opens it shouldn't overheat

[dan4836]

If I take out the thermostat, the coolant will go where it wants. Some will go to the exchanger and some will go back through the engine.

[macojoe]

Make sure the T stats are in the right way! I have seen people put some in backwards and they can't work right! Can't do it with all but some you can, worth a try.
Are you sure the T stas are opening?? take out and put in boiling water see if they open and close when they get cool? Might need new ones?
Motor water pump, mine had the impeller rot off it and could not move the water, someone had put a auto water pump on it.

[dan4836]

I had a marine mechanic come over to take a look and this is what we found.

The thermostat that is installed does not look correct and I was to purchase another thermostat for the 470 that looks like it will do its job. The new thermostat part numbers match up with the newer, aluminum manifolds.

From what we see, the part number of the thermostat installed is the correct part number but it does not look like it will redirect the coolant to the heat exchanger.

The mechanic said my setup is unusual because the thermostat does more than one function. It lets water go to the heat exchanger and closes the hole the goes back to the engine.

I will see on Saturday during a test ride...

[dan4836]

Found my problem! After replacing just about everything, I found my thermostat is incorrect.

I researched this for weeks and found the thermostat my engine calls for matches to a Mercruiser part number that is incorrect. I put the thermostat for the newer, aluminum type manifold in my older cast iron type (first generation 470) and it worked perfect. 170 degrees at 4000 RPMs for ten minutes.

I wonder how many other people are using the incorrect thermostat in their 470 based on Mercruiser's numbers.

Now I can post about other restoration projects and maybe show some fish pictures this year!

[aussie]

Glad you found the problem will have to make sure I use the correct one Hey spares no input from you on this one