1988 merc. 470 help needed 3.7 Temp to hi.

[alex3012red]

I have a 470 that was rebuilt,(new bearings .010, pistons are std,rebuilt head, new seals with reedy sleeve on water pump shaft. cleaned out 4" heat exchanger.(took ends off looked o.k) pressure washed it. new thermostat 160 deg. new impeller. no leaks either oil or antifreeze on cooling system. Can't get temp below 190 deg. idling and goes to 200 deg when running 3K or above rpm under load(2 adults). I removed the hose before the heat exch. too see if I was getting water from impeller, it seem a good flow.also tried to put more water in the heat exch. temp idling was still 185 deg. gets hot moving.
Can the heat exch. be taken apart? to clean out, seems clean to me but i can't see everything from the outside. Any expert help would be appreciated. thanks

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

I also had carb rebuilt, new plugs, timed at 4 deg, and tried 8 deg. no diff. and new temp sending unit just in case i was getting a wrong reading. I have a 3" heat exch. from an older engine, should i try that one to see if it's better( less clogged in case it's clog) not sure. engine seems to make pinging noises when temp is higher than 190. very min. I may just be nervous. Please help!

 

[Don S]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

What shape is your exhaust riser in? if it's all plugged up and restricting the water flow, it's going to overheat.

 

[rodbolt]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

have you checked the riser for clogging, especially if its a saltwater boat.
doesnt matter how much water you can get in,if you cant get it out it overheats.

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

when the engine was rebuilt, i did a visual on the riser it look good, no excesive rust ont it. and it is a saltwater boat. how can i better check the riser?

 

[zbnutcase]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

I would replace riser. 'nutcase

 

[Don S]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

when the engine was rebuilt, i did a visual on the riser it look good, no excesive rust ont it. and it is a saltwater boat. how can i better check the riser?

The rust on the outside means nothing. The inside water passages being plugged up can be your problem. Look at the water exit on the riser, that is where you can usually see them corroded and plugged up the most.
But, as noted. If you are rebuilding an engine, put on a new riser when it has been in salt water. 6 to 8 years is about all they last in salt anyway.

 

[achris]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

.... 6 to 8 years is about all they last in salt anyway.

And they don't tell you that in the sales brochure!!!

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

thanks, i'll start shopping for a new one!

 

[sdoomaha]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

You have had this problem since you had the motor rebuilt and the engine put back together? Who put everything back together for you? Only reason I ask is if it is problem since the rebuild, you may want to check the gasket between the exhaust manifold and the riser/elbow. There are 4 passages, some are left open and others are blocked by the gasket. If you are blocking the wrong passages, you will overheat. I had a very similar issue occur after I replaced the gasket between the two when I was in the process of changing the head gasket on my 470. Very similar overhetaing problem...took me forever to isolate the error I made....but a quick gasket replacement the CORRECT way, and she has been running super cool ever since. Might be worth double checking.....it might be a cheap easy fix.

Good Luck.....

 

[Don S]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

thanks, i'll start shopping for a new one!

Why would you want to go buy a new one? you don't even know if your present one is the problem.
You have only had a few suggestions as to what could be wrong. Why don't you check things out, find the problem, then fix that problem, instead of throwing expensive parts at it and hoping for the best. That gets very expensive and usually doesn't fix the problem.

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

thanks Don, i did took the riser off today and it looks very clean no major rust, what I also saw was that the flapper is melted away in the exhaust, i'll take the pieces out,and replace the flapper. could that have an effect of temp. The gasket looks to be in the correct side it block the rear passage, if i were to put it backwards the shape is diff.

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

and yes the overheating started after the motor was rebilt.

 

[achris]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

and yes the overheating started after the motor was rebilt.

So, check valve timing, ignition timing... ect... The back of the service manual has an excellent troubleshooting guide...

 

[Big D MacG]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

Did you change the impeller in the bottom end, it may look like alot of water but maybe no preasure. If you run that motor for just a minute with no hose on you will burn that impeller. I would look hard at the bottom end pump.

 

[Big D MacG]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

P.S if that flapper was melted there was no water.

 

[alex3012red]

Re: 1988 merc. 470 help needed 3.7 Temp to hi.

big d i did change the impeller on it after the motor was rebuilt, I changed the whole pump unit, I will recheck the impeller to see if any wear on it from trying it out. and replace the flapper.