help! mercruiser 470 cooling issuies

[slimsilver1]

im new to this whole boating thing but engines i know. i work on cars all day long , i just purchased a 1978 bayliner with a mecruiser 470 that has over heated since day one. i replaced the water pump & impeller in the lower drive unit which at first i thought solved the problem until my temp. gauge started irratically moving up and down then overheated. ive since checked for restiction, checked and cleaned heat exchanger , and pressure tested for possible blown head gasket. i cannot find anything.am i missing something? also this engine to me seems an awfull lot like a gm 2.5lt.(iron duke)or am i wrong?

 

[Don S]

Re: help! mercruiser 470 cooling issuies

The Merc 470 style engines are unique to themselves, and have nothing to do with the GM "Iron Duke" 2.5 and 3.0L engines.<br />THe 470 has an aluminum block and basically a 460 Ford big block head.<br />They suffered from overheating problems, and coolant leaks into the oil. The charging system was taken out of an outboard book with the stator rotor charging system on the crankshaft, and "IMHO" was just a horrible experiment by Mercruiser.<br />BUT..... Lots of people swear by them instead of at them like I do. So don't take everything typed on these forums on what others think of a particular type engine as gospel. Youu may get many years of great service from your engine. Just depends on your luck and the types of preventive maintenance you do on it.

 

[Haut Medoc]

Re: help! mercruiser 470 cooling issuies

I would say that you should take the haet exchanger to a radiator shop and have the FWC side rodded/boiled out.......JK

 

[MrBill]

Re: help! mercruiser 470 cooling issuies

It sounds like there is definitely restriction in cooling flow, but it does not sound like you isolated it to the raw side or closed side...for starters.<br /><br />First, has an alternator conversion kit been installed? If so make sure the old water cooled regulator has been by-passed.<br /><br />Next check the engine on muffs, if the pressurized water keeps it cool, you might be able to isolate the problem to the raw side. I know the boat won't be under load, but it's a short cheap test.<br /><br />Is the closed side circulating properly, you did not mention thermostat replacement, try removing it, usually this makes the enginge run a little cool (not recommended for permanent running).<br /><br />I understand how perplexing the cooling issues are on 3.7 liters, the 3" heat exchanger is marginal at best.<br /><br />Also check restriction in exhaust, the flapper should be in place, or maybe it's lodged down in the lower unit. Be patient...you'll resolve the issue, us 3.7 liter lovers always do...

 

[slimsilver1]

Re: help! mercruiser 470 cooling issuies

well i tinkered around a little today. it runs fine stays at about 160 deg. with muffs on.(raw side issue right?)so instead of forcing water in i filled a tank with water and let her run.it sucked water very well on its own , but after about 10-15 min circulation came to a stop - no water coming back out. hook the muffs back up and all is well. any suggestions???

 

[Pst76]

Re: help! mercruiser 470 cooling issuies

Sounds like a bad impeller,slipping or spun? forced water (Muffs)would help rotation pushing water into intake. In the tank impeller would have to pull water in and push on its own. Just guessing but that would be what I would look at first.

 

[MrBill]

Re: help! mercruiser 470 cooling issuies

Slim....sounds like you're getting closer<br /><br />Two things to check that are relatively simple:<br /><br />Take off the water pickups and try to see if there's a restriction just inside, before the impeller.<br /><br />Next remove the upper exhaust tube that joins the upper exhaust pipe and riser and check for anything in there, and if the water level is below the lower exhaust tube (top of lower exhaust pipe) remove that too. Check if flapper is in place, if not, is it down in there? Maybe it got partially cooked and is lodged down there wit the metal arm that is supposed to hold it in place. <br /><br />If these don't "pan out", I think you'll need to head inside the lower unit and re-check the impeller and water tube, if you checked the other things mentioned in my first response. Make sure that impeller is in good condition and fully engaged when the shaft is rotating (not spinning freely). Spin the prop and make dam sure the impeller is tight. The impeller is so critical to closed cooling systems that minimal wear from sand, etc can cause problems.<br /><br />Let us know how you make out.

 

[slimsilver1]

Re: help! mercruiser 470 cooling issuies

first I would like to say thanks for all the advise. I am in the middle of a total tear down of the cooling system, its all getting boiled out or replaced. The only problem I have is a broken bolt in the thermostat distribution housing , that also now has my broken easy out in it as well.I figure just replace it , its rotting any how.Only thing is I cant find one. ANYWHERE! <<<anyone have any leads? >>>

 

[Haut Medoc]

Re: help! mercruiser 470 cooling issuies

How bad is it? (the fitting) drill out the easy out & save the fitting...When you drill out a bad bolt, the best thing you can do is get as close to the original diameter without buggering the threads...Then run the right tap through it...With a bad easy out ths will be hard now...If I'm reading this right you have broken it off in the block...You need to center it exactly before you drill, and have patience, and more than one bit....Take your time & good luck...JK

 

[slimsilver1]

Re: help! mercruiser 470 cooling issuies

the broken bolt and broken easy out are in the thermostat distribution housing, and since the easy out is a hardened steel drilling is now out of the question. i also thought about blowing it out with some heat but the housing is alumnum. not a good idea. if i cant find a replacement im really going to have to try something.

 

[bigbrownbuku]

Re: help! mercruiser 470 cooling issuies

sounds like a classic air leak on the pickup side. use clear hose to narrow it down. <br />when the raw water pump was rebuilt was the plastic base lifted and the gasket replaced? does the engine have the larger style heat exchanger? make sure the bypass tube from under the intake manifold to the header tank is clear at both ends. check your cap will hold the correct pressure. check your cooling system will hold the correct pressure.

 

[Haut Medoc]

Re: help! mercruiser 470 cooling issuies

Can you see any light? Some wd 40 and an awl to shake it loose? You can drill throgh anything if you have enogh bits & patience....If it is metal it can be drilled...But an ez-out remover? Rodbolt,Bondo,Don S.-Help!~......JK

 

[MrBill]

Re: help! mercruiser 470 cooling issuies

Which part do you need?? Here's link to MercruiserParts.com<br /><br /> http://www.mercruiserparts.com/Show...+MANIFOLD+ASSEMBLY+AND+EXHAUST+ELBOW+ASSEMBLY