Mercruiser 470 cooling question

[Merc470]

I recently purchased a boat with what I believe is a Mercruiser Model 470 engine and sterndrive. Engine# A474717 Transom#A466505.

It will not draw water out of the lake and heats up quickly but if I hook muffs to it water will circulate and it stays cool.

I'm assuming there is something possibly wrong with the impeller in the lower unit and would like to replace it. I would also like to replace the impeller in the engine also just as a precaution.

Any idea what part numbers I need to look for to replace these two things.

Thanks, Ben

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 470 cooling question

The engine impeller is made of aluminum and doesn't wear out like the drive's impeller which is rubber. The complete water pump kit is the way to go, and sold right here on iboats:

Alpha one lower unit without the preload pin use this kit:
http://www.iboats.com/mall/partfind...&gd_poid=110924&gd_row=3&**********=073041740

Older MC-1 lower units with the preload pin use this kit:
http://www.iboats.com/mall/partfind...&gd_poid=110922&gd_row=2&**********=073041740

You can determine which you have by identifying your drive:
http://www.mercstuff.com/drive_id.htm

There are a couple of things that these engines have issues with:

sensitive to overheating, causes damage to heads and gaskets, Dont let it get hot!!! Always drive with one eye on the temp gauge, and make sure it IS working.

Factory charging system is very costly to replace if it fails. There are aftermarket conversion kits to add a belt driven Marine alternator.

The seals on the engine camshaft tend to cut grooves and weep water out the weep hole under the water pump. The grooves are in the camshaft and new seals alone will usually still leak. Keep an eye on it.
Have FUN,

 

[EddiePetty]

Re: Mercruiser 470 cooling question

......
It will not draw water out of the lake and heats up quickly but if I hook muffs to it water will circulate and it stays cool.

I'm assuming there is something possibly wrong with the impeller.......

Thanks, Ben

I believe you assume correctly.

The water pressure from the hose on the muffs will allow water past the defective pump impellers, thus sending fresh water to the heat exchanger to cool the engine coolant. When waterborne, the impeller has insufficent flex in its vanes (if there are any left) to sent cooling water to the heat exchanger. You will probably need to replace the complete pump. Parts are available everywhere. I would suggest OEM parts however.

Be advised, once you have the lower unit off the outdrive and the pump disassembled, if ANY of the impeller pieces are missing, you MUST find them as they can block cooling water. The most likely place for them to lodge is on the inlet tube sheet of the heat exchanger.

If the engine really overheated, examine the exhaust passage in the outdrive for pieces of the former water shutter (flapper) valve and do a compression test to check for head gasket leaks.

Here's a How-to for replacing your pump......

http://www.mercstuff.com/waterpumpinst.htm​

 

[Merc470]

Re: Mercruiser 470 cooling question

My computer won't allow me to open that ID link, is there something specific I need to look for?

Pretty sure it is an 1985.

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 470 cooling question

Try this one:
http://www.mercstuff.com/howdoi.htm

The thing you need to know is if the lower half is alpha one or older, with or without the preload pin. They are interchangeable so even if the engine is '85 the lower can be from a older model and bolt up. Easiest thing to do is drain the lube and separate the halves and look for the pin, so you can order the correct kit.

There is a link at the top of this forum Adults Only, in there is Miscelaneous Mercruiser Info and this link to identify which drive you have:
http://forums.iboats.com/showthread.php?t=329915

 

[Merc470]

Re: Mercruiser 470 cooling question

Thanks guys,

I believe it is a MR but won't know for sure until this evening.