More overheating 470 thoughts

[Peabody]

Okay...I have read lots on the overheating problem that these motors seem to have...now I am getting a little mad, even, because this is a motor, and it should be capable of running for an afternoon without trouble.<br />As near as I can figure, mine cooks when run at over 3,500 rpm? Is that the rev limit, or do they run faster when correct?<br />I believe that I have done the usual that are outlined here...last season a boatyard replaced the exhaust elbow. I have replaced the outdrive impeller this year, and know that it pumps with authority. I have also replaced the 3 inch heat exchanger with a new 4 inch unit. The internal water pump works...pumps a lot.... The condition exists when the 160 degree thermostat is in place or not. Timing is correct. <br />Is there a schematic anywhere that has details of the cooling routing....???? I have the Clymers manual....<br />Thanks a bunch.<br />Peabody

 

[achris]

Re: More overheating 470 thoughts

Mr Peabody,<br /><br />If you post the serial number of your engine and your e-mail address, I'll send you the flow diagram.<br /><br />Chris...........

 

[hondon]

Re: More overheating 470 thoughts

If all is stock you will also have a water cooled voltage regulator that could cause a circulation problem.

 

[Peabody]

Re: More overheating 470 thoughts

Hondon....<br />The engine has an alternator hanging off to the side, and I remover the old regulator entirely from the boat....thanks.<br /><br />Chris....I appreciate it...I had the s.n. written down, but like major portions of my mind, I seem to have lost it. I will get it today.<br />Thanks

 

[Northern Eclipse]

Re: More overheating 470 thoughts

Peabody, you state the motor cooks at or over 3500 rpm, What is the temp readings?, if your getting 170-180 your still good, also you state timing is correct, whats is it set at? Merc issued a TSB for timing, they suggest 2*- 4* old specs are 8*-10*, also the antifreeze mixture should be 50/50, strait antifreeze or near strait will not have good cooling capabilities. This motor should rev up to 4200-4600 WOT.

 

[Bob_VT]

Re: More overheating 470 thoughts

You have two water pumps. The impellar is one and the other is in the motor. If the one in the motor is failing then you are not getting proper circulation in the motor. If the impellar was failing you would not get proper circulation in the heat exchanger. (incidently the heat exchanger can go bad and get clogged a good item to check too)<br /><br />bob

 

[kcole683]

Re: More overheating 470 thoughts

Depending on the year of your 470 it may have an undersized heat exchanger.<br />Check to see if you have an old 3 inch exchanger or a newer 4 inch .<br /><br />I have a 1985 170 horse 3.7 that will run for hours at 3500 rpms without overheating. I can run at 4000 without any problems either. If I run if wide open at 4500 to 4600 rpm it will warm up 185 to 190 degrees.<br />The thermostat starts to open at 160 degrees and is all the way open at 185.<br /><br />Check for sediment build up in the bottom of the circulating pump at the drain on the bottom. You might want to fluch out the closed system too and check or replace the thermostat.<br />Of course none of this will do any good if you have low flow from the stern drive pump or if there is a restriction anywhere in the seawater system.<br />good luck

 

[kcole683]

Re: More overheating 470 thoughts

oooops!<br />I see I have been skimming again and not reading the whole post.<br />You have a 4 inch exchanger thats good.<br />If you remove the thermostat on the 470 Mercruisers I have read it will definitely overheat without it.<br />The clymers manual ahould have a flow diagram of the cooling system.

 

[Peabody]

Re: More overheating 470 thoughts

Thanks...<br />I had a nice time on the Hudson yesterday, kept the rpm's below 3500 and had not problems. Currently have no thermostat in the system, and the kid took the timing light to fool with his motorbike....<br />The clymers manual shows seawater going into the exhaust manifold....not exiting. Does the exhaust manifold get full of crap and scale? If so, is removal and either soaking in acid and/or trying to dislodge it a do-able deal, or is a new exhaust manifold in my future. <br />I'm a car guy, and sell diagnostic software....I don't mind spending the $$$$$ if it will correct the problem.......right now it seems as if I am shooting into a barrel.<br />Thanks for the help! I really appreciate it.<br />Peabody

 

[imported_Mike_M2]

Re: More overheating 470 thoughts

I would check the exit of your manifold. That back section unbolts and thats where the raw water mixes with the exhaust. They tend to clog up after a while and it may need to be cleaned out. As you stated above it gets like a hard scale there. What i use is a medium coarse round file and clear the slots. This would cause just the problem you state above so hopefully it'll cure it!

 

[Peabody]

Re: More overheating 470 thoughts

Mike...<br />Is the part that you mention the "exhaust elbow"? If so, mine is new last season...less that 50 hours ago.<br />Thanks a bunch!<br />Peabody

 

[seahorse5]

Re: More overheating 470 thoughts

It's been a while since I've worked on those Merc 4 bangers, but the 470 had the distinction of having the most service bulletins on one engine.<br /><br /><br />One of the items to check is to make sure anti-freeze crystals did not form and plug the bleed hose and internal passages. That was a common problem back in the '80s. Put the correct thermostat (there are several) back in the motor. Head gaskets were a problem, especially if the motor overheated at one or more times.

 

[Peabody]

Re: More overheating 470 thoughts

Seahorse...<br />I will put the thermostat back.... The system has integrity...frequently cracking the radiator cap results in a sucking sound, indicating to me that there are no leaks, anyway, including being able to exclude the head gasket. The bleeder deal is a mystery. I'll look at that, too.<br /><br />Thanks <br />Peabody