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Mercruiser 470 Overheating

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PowerBoat007

New member
Hello Fellow Boaters,

I am new to this forum, but it looks like a lot of you guys out there are very knowledgeable and can help me (I am new to powerboating).

My wife and I recently purchased a 28.55' Bayliner Express Cruiser, and it came with twin 470 Merc's. The seller advertised it as "one engine working and one engine not" which happens to be correct.

However the engine on the left side of the boat,which appears to be attached to the Hot Water heater (the "working engine") overheats almost immediately after starting it.

I replaced the coolant, but no luck. On a sidenote, our water heater works great, and I was thinking that since it is plumbed to the water heater (which by the way has very hot water in it right now) might be causing part of the overheating problem.

Also, the non working engine was advertised as having been overheated at some point and that is the cause for it not working (won't even crank).

Anyone have any tips as to whether I should try to get these running as in "simple fix" or should I just get new engines?

What are recommended replacements for this type engine (preferably to increase the horsepower in so doing).

Thank you!
 
hot engine:
replace impeller in drive, inspect power steering cooler for clogs, inspect/replace riser(clogged)
non working engine:
pull spark plugs and try to turn over,if anything does come out , pull the heads for inspection.
 
Ok...I am not really a mechanic, but I am downloading a Merc 470 manual. I assume the riser is the high part above the engine where the exhaust goes through?

There is a cylinder shaped object along the side as well, which I am assuming is the exchanger. Should I check that as well?

Also, if I want to back flush my raw water which hose do I flush from?

Thanks so much Bt!
 
The riser is the part that aslo has the radiator cap. It`s a split setup.
The power steering cooler(if equipped) is about 4-5 inches long and 2 1/ in dia.
The heat exchanger is 4 in x 36in. and is on the port side of the motor
Start by replacing the impeller, with the drive off the boat you can insert a hose into the water inlet hole and test run the motor at any rpm .Backflushing can mask a bad pump.
 
Powerboat07

Here is my opinion take it for what it is worth

You bought yourself a very very large problem...........the 470 engine is a problematic motor at best for most. Not all but for most.

You need to either find a very knowledgable marine mechanic on that vintage engine and drive or sell the boat and buy one that works...........

This will become a money pit for you.................just sayin.
 
As far as engine repower goes.........

A boat of that size SHOULD have twin 454 cubic inch motors and bravo 1 outdrives at a minimum.

Probably cost about $20,000.00 to do.

You could go to 350 cu inch motors and correct gear ratio drives for about the same cost.

Again this will be a money pit.


Rule of thumb, of course this is my thumb.

16-18 ft boat 4 cylinder motor OK
18-20 ft boat v6 motor
20 to 22 ft V8 small block 305 to 350 cubic inch
22 to 30 a 454 or 502 BIG BLOCK
Large boats with dual engines 24 ft and above twin small blocks minimum better with big blocks.

You need lots of torque for a large boat.

That boat when built was built for price not practicality!!!
 
If you replace the engines with something larger in a V configuration, which is all that's available, you will probably have to have the current transom holes filled and recut. The new engines will have to be mounted further apart than the inlines you have. Also will require new engine mounts be fabricated and glassed in. And should be complete packages (engine, transom plates, drive) as those old drives will not handle the increased power/torque. Not an inexpensive process.
 
ok...I have same problem with my Mercruiser 470...it is overheating with fluid out of radiator cap. Engine temp reached 240 degrees before I noticed it. I am suspecting impeller because I found chips in the outboard unit where the muffs go. My question is, is the impeller in the outdrive or is it on the engine?

I checked the oil after it reached 240 and it was clear as it could be, so I'm thinking no issues....

anyone have any thoughts?
 
markc1216 said:
ok...I have same problem with my Mercruiser 470...it is overheating with fluid out of radiator cap. Engine temp reached 240 degrees before I noticed it. I am suspecting impeller because I found chips in the outboard unit where the muffs go. My question is, is the impeller in the outdrive or is it on the engine?

I checked the oil after it reached 240 and it was clear as it could be, so I'm thinking no issues....

anyone have any thoughts?
Click to expand...

the impeller is in the lower unit ...with the muff's on do you get good flow out the prop? open the heat exchanger to see if it is plugged with debris ..end caps ..

you will need a manual if you are to replace this impeller ..
 
Ok new to boating. First let me start by saying I have a 25 ft regal ambassador with twin 470's. It does close to 50 with 4 people on it. Plenty of power. Second, I have owned this boat for 10 years, it is a 1990, I don't know where these motors were sitting, considering they stopped producing them in 1988 and my boat is a 1990, but I have had no problems with them until this year. I did not check my riser on the starboard engine and it let water in my oil. So I pulled the motor and had it rebuilt or remanned however you want to say it, but it is totally new. It cost 1800.00 to do it. I put a new manifold and riser on it and it is back to normal. I don't understand where all these guys get there info on these motors. Yes they need maintenance, but don't they all. So here's the things that need to be addressed with the motor. First alternator should be converted to belt driven type. Second the fresh water pump will probably fail and need repairing. (The cam seals will start to leak). Again repairable. Third the risers need to be replaced every 3 years depending on usage. That's about it, they are fresh water cooled and I have boated year round with them. Oh by the way how many small block Chevy's crack every winter because someone or some legit company doesn't winterize them properly. These motors maintained properly will without a doubt outlast any small or big block out there. So there you have it from a happy owner of 2 3.7l mercruiser motors. They should still procuce it, if you ask me, but I guess 3.0 blocks from GM are cheaper. See ya.
 
Now that you have heard all the knights of the boating table, here is my 2 cents: Before you do any work on engines and ODs, check the condition of the floor, stringers (floor joists) and transom; you are looking for rot. Very expensive to repair.

Next, reman. 470 3.7L engines are available for under $2500 each. New ODs are available for under $1400 each from SEI. So, you could completely repower for $10,000 to $13,000 w/the same powerfull 470 engines the boat came with. I'm not a fan of the 470.
 
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