First boat, 1980 mercruiser 470 overheating, need advice

soiwait · Aug 7, 2012

Hello. First post, first boat. I know next to nothing about boat engines except what i have read over the last 2 days on the forum. I got a 17?ish foot 1980 sea ray with an easy load trailer as a trade. It has Mercruiser 470 serial #5536XXX. Runs great with muffs, starts right up. New interior, one of the cleanest boats I have seen. The guy I got it from said he took it out on the water and it runs fine except it overheats. He said I just need to replace the impeller and it should be fine. After doing some research, I am not so sure. The coolant (overflow?) tank has a hole on the top of it as well, if that would affect it at all.

I have a couple questions:
1. Where can I get an impeller kit that will work for my engine?
2. If it's not the impeller, what are some cheap ways to see what it could be? (I'm 21 years old and have no money)
3. If there isn't a cheap fix, should I just punt the whole package as an overheating boat? Is it worth it to save up and try to fix it (it would take a long time with my income) or part it out? And around how much should I ask for it if i sell it all together?

I will post some pictures of it if that would help. I would love to hear your thoughts.

Bt Doctur · Aug 7, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

we were all 21 and broke at some point!!!!!!!!
post 2 in here for a manual link for the drive. http://forums.iboats.com/showthread.php?t=554934
manual 8 for the engine in here, view only.
get an impeller kit and some gear oil and give it a chance. http://boatinfo.no/lib/library.html
lots of reasons to run hot. no water in, no water out, no water circulating.

soiwait · Aug 7, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

So is the motor I have not the original? The boat is a 1980, but the #8 manual is for 1985-1989. and how do I know what impeller kit to order? there are some with a bunch of different gaskets, and some with just one or two, and some with different sizes.

Bt Doctur · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

old and blind ,what a combination.last time i screwd up the 3 and 8 a judge issued a warrant on me
try manual 3

Don S · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

(I'm 21 years old and have no money)

And you bought a boat with a 470 in it??????????? Oh man are you in trouble. The 470 is a maintenance consuming, money hungry engine, that absolutely hates overheats. It usually means the head gasket will have to be replaced. The open deck design of the aluminum block and cast iron head just lets things move around too much when overheated and the head gasket starts leaking and causing more problems.

You need to remove your drive and take the upper off and check the pump and see what all is wrong, BEFORE you order parts, or you could be spending more money for more shipping after ordering the second time.

Cheap and boat do not mix. You can fix it a less expensive way, but it's still not cheap.

Manual 3 is the manual you want for the engine, the drive would be in manual #4
Both are here http://boatinfo.no/lib/library.html

Oshkosh1 · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

The guy I got it from said he took it out on the water and it runs fine except it overheats.

Define "overheats"...a SPECIFIC temperature.

Overheat as in "it's getting hotter than normal"...or "it gets HOT!"

Run it on the muffs and tell us what the temp gauge stabilizes at, OR if it gets to 200deg...shut it off...it's "HOT!"

Regardless...if you don't know for sure when the impeller/housing were replaced...replace them. While you have the drive off, grease the u-joints & splines, inspect the gimbal bearing and alignment.

Eric 3.7LX Alpha 1 · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Pick yourself up a Mr. Gasket thermocap which will replace your existing radiator cap with one with a built in thermometer. You can use it to confirm your dash gauge is accurate.

They come in different psi ratings to match what your existing cap is rated for.

soiwait · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Ya I wish I had done thsi research before taking the trade for the boat. So is this thing worth anything as it sits right now? I would love to get it running right but it seems like that might not be an option.

Oshkosh1 · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Yeah it's worth something. Just don't be in a rush. Solve one issue at a time. The most important is the overheating. As I stated before, regardless of whether it was overheating or not, the impeller et al should be replaced. Use the above cap, or get an IR thermometer to confirm the gauge.

stonyloam · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

OK don't panic. A 470 normal operating temperature is 165 t0 200 F, so what would be a overheat condition for a raw water cooled engine is OK for a 470. Go over 200 and you are probably screwed. Pull the outdrive and change the impeller, cost about $35, lube the U-joints and driveshaft splines. Start it up on muffs and do a compression check and cooling system pressure check (you can borrow the tools from autozone). Check the impeller for missing pieces when you change it. If hunks are missing look for them behind the front cover of the heat exchanger. Good luck, and welcome to the "470 Club":facepalm:

soiwait · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

For the temp on the muffs, should I just let it idle or put some rpms on it? and how much?

stonyloam · Aug 8, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Trim the outdrive down as far as it will go (and not hit anything), not over 1500 rpm.

whatsagm · Aug 9, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Dont listen to the nay sayers the 470 is a good engine when it has the updates. I have one that i bought with a broken engine. I rebuilt it and had the cam journal weld up with a silicone base weld so the seals will not eat into the cam. I also did arp head studs. I did the one wire alternator conversion to upgrade the charging system. I added the 4 in heat exchanger. I also did the pertronix electronic ign. My 470 runs like a top and is very reliable. Good on gas and plenty of power. Mine also used to run warmer than normal and the Impeller was worn so I changed that out. I have 2k in the boat total.

stonyloam · Aug 9, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

whatsagm said:
I rebuilt it and had the cam journal weld up with a silicone base weld so the seals will not eat into the cam.

I also did arp head studs.

A little more information on these two please. Sounds like you know what you are talking about!

whatsagm · Aug 9, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

My machine shop that is a good friend of mine put my cam in the crank ginder and ground down the journal that the seals were starting to eat into. He then builds it back up with a silicone based weld and regrinds it to size. The weld is so slippery that the seals cannot eat into it. He does this on crankshaft rear main seals. I also used arp head studs from a ford 460. The head studs allow for a better clamping force preventing the gasket from wearing out. The studs are not a total fix but its better than the bolts. As soon as i get a good deal on an aluminum head im going to put one on so then there will be no gasket issue anymore.

soiwait · Aug 9, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

I ran it on the muffs today for about 15 minutes. it steadied out at about 170 degrees idling, and about 180 degrees at 11-1200 rpm. So it seems as though it isn't overheating. Although who knows what will happen on the water for real. I'll replace the impeller and housing and see what happens the first time out.
Do you think i should fix/replace the coolant overflow tank? I also noticed today that it doesn't have a cap either, besides the hole in it.

stonyloam · Aug 10, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

soiwait said:
I ran it on the muffs today for about 15 minutes. it steadied out at about 170 degrees idling, and about 180 degrees at 11-1200 rpm. So it seems as though it isn't overheating. Although who knows what will happen on the water for real. I'll replace the impeller and housing and see what happens the first time out.
Do you think i should fix/replace the coolant overflow tank? I also noticed today that it doesn't have a cap either, besides the hole in it.

That sounds pretty good, the raise in temp is not too bad, but shows that it could be working better, with the new housing and impeller you should be OK. Yes you need the overflow tank repaired. It works the same as the one in your car. When the coolant is at the proper level the reservoir should be full and the tank should be filled with coolant (50/50 auto antifreeze) to the fill line. When you run the engine the coolant heats up and expands and the excess coolant flows from the fitting at the cap through the tube attached the bottom of the tank, raising the level in the tank. When the engine is turned off the coolant cools and contracts and draws the coolant from the tank back into the reservoir, that way the system always stays full. So you need to make sure that the hose from the reservoir to the tank is in good shape and goes to a tube or fitting that can suck the coolant out of the bottom of the tank. The cap is not important anyone that will fit will do just make sure it is vented. If the tank is trashed, one from a junkyard (auto parts store should have a generic one that will work) will do as long as you can mount it where it will be about level with the current tank.

whatsagm · Aug 10, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

I bought my over flow tank at autozone. Cheap and works well.

soiwait · Aug 10, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

Took the lower drive off today. First off, it is missing two nuts connecting the top and bottom of the drive. that should have been a clue. Then to my surprise, all the rubber looked brand new. I took the water pump housing off, and found a nearly new impeller that looks like a mangled star fish. half of the fins are twisted or turned the wrong way. the housing also looks almost new. all the gaskets have no wear on them. So I'm hoping i just need a new impeller, not the whole kit. Here are some pics of the impeller and the housing. Let me know what you think.
Also, which way are the fins supposed to be facing? so I don't do what the guy before me did.

stonyloam · Aug 11, 2012

Re: First boat, 1980 mercruiser 470 overheating, need advice

You turn the driveshaft CLOCKWISE when you instal the impeller (push the housing down over the impeller, a little grease on the fins helps), so it should look like the last photo from the top. You can see that old impeller has taken a "set" and the fins are no longer flexible. Yeah the new impeller/gasket set should do the job.

First boat, 1980 mercruiser 470 overheating, need advice

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