454 mercruiser running hot "update"

D

D. Andrews

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7.4l mercruiser carbed, fresh water cooled, bravo outdrive, running a bit on the warm side. It has done it since I bought it last year. It will hold 170 at idle all day but when you get it up on plane, it gets to 190. Put it in shop and had the impeller changed. Get it out, and it is worse, a bit over 200 at 3k rpm. Marina says the water pump is bad, need to replace it. Changed out thermostat last night at the marina, test drive it this morning. Its better, but not right, can get planning speed but anything over it gets hot again. So I pull it and bring it home. Pull water pump, impeller looks great, I look inside of heat exchanger and there it is, white rocks clogging the tubes.

My question is how to clean it, it is a 3 pass heat exchanger, raw water side has either a calcium or lime build up. I am thinking of standing it on end, plugging the bottom hole and filling it with CLR for a couple days. Any body got any better ideas? Anyone ever done this before? Thanks in advance..........D...........
 
Years ago I took a problem heat exchanger to a radiator shop, they cleaned it out, but I can't remember any details of what they did to it. There aren't that many radiator shops around these days though. I've also cleaned one out myself with acid, I don't think it was muriatic, maybe phosphoric or something ?
 
Any acid will work to dissolve lime/calcium/base build-up. Better to use a more dilute mixture.

The tubes are 1/4" so a 1/4" all-thread or something similar should clean it up in no time.

An FYI for leaks in the tubes, get a 1//4" brazing rod cut to equal length of the tube, insert the rod and solder both ends.
 
Charlie, I have already done that with the rod. Problem is that there is a chamber on one end that does not come off where 2 of the passes meet. meaning it is full of the stuff. I flushed with water and it just blocks the holes up again. Got to get something in there to disolve the stuff or at least make it small enough to flush out..........D.........
 
Like Andy said, some radiator shops still have boil out tanks. That'd be your best bet.

BUT, Both side of your heat ex should open up. Mine has the 4" by 3 pass and both sides open.

If you're gonna clean out with acid, do a check about the susceptible of lead solder to burn away with strong acid.

How about scrapping some of the white stuff in a jar and put vinegar in to see how that works.
 
Only one side of mine comes off, the other side is welded. It is in the garage now full of clr, did not even get a full gallon in it in all 3 passes. I figure on letting it sit over night, but will check it every so often to see how it is doing. It did a good bit of bubbling at first, but settled down a lot after a few minutes.

Ordered new water circulating pump today too, going to change that out also, got it off, might as well. The front bearing was a bit noisy so. Will keep it as a spare just in case. Boy do they like those.........D.........
 
What about a low pressure pump attached to one end of the exchanger in a bucket of acid or CLR. Friction may wear or loosen he clog. Beyond that, I second the radiator shop. A schoolmate still does the procedure in the shop his father started decades ago. Fishermen depended on him......still do!
 
I just used Barnacle Buster circulated thru my A/C coils
with an aerating pump. I did it for 4 hours and it cleaned out a lot of crap.
 
There are no radiator shops left in my area. The EPA took care of that, not even any shade tree ones left. I let it sit over night and took a rod to them at random just to help it along. I will let it sit for a few more hours and take the water hose to it. Getting all the tubes clean is the easy part, it is getting the stuff out of the one chamber I cant get to thats the problem as I know I will just clog it right back up again..........D.........
 
Dang, can you tell if the crud is just in the heat Ex? Like where is it coming from? Has the raw water ever been checked for hard water?

Did you remove the hoses from the raw water inlet side and the outflow. The inlet should be about 1 1/4" so it ought to back-flush pretty good.
 
The radiator shops around here cater to large trucks and diesel-powered industrial equipment, all of which have big radiators. I took my clogged Sen-Dure heat exchangers to a local shop who did the exchangers on my previous boats. Took him two days and they looked like new. He charged me $100 for doing both. He left the end caps off so I could see what they looked like inside.

Bill
 
Clr worked like a charm, inside looks brand new and flows great, only a powdery residue washed right out of it. Will start reassembling the boat wed. Looked at the inlet and outlet, and they are clean and free, it is just in the heat exchanger.........D...........
 
Greg,
I think D got the answer. Pour clr into the lake.
 
Got it back together last night, ran on the muffs for about an hour, ran great. Will relaunch today and that will be the real test.........D.........
 
Well no change. Will stay at 170 puttering around all day. Go to plane speed or wot and to 200 she goes but never goes over that no matter what I do. I tried to get it to get hotter and it stays at 200. Doesn't act hot or run weird so I am beginning to think that is just the way she likes to be. Could be the riseers I guess? Ran about 10 miles yesterday at wot and stayed at 200 the entire time. Any thoughts?.....D.....
 
Just a thought, but could the antifreeze mix be greater than 50/50? Anything greater than 50/50 and it won't cool effectively. Great freeze protection , but not much cooling.
 
Gotta backflush to locate any blockage. Oil or power steering coolers are things that can clog. Do you have a thru hull pick-up along with the drive pick-up?
 
Anti freeze mix was probably 100 percent when I started. Now it is about 50 50 if not more water than antifreeze.

No through hole pickup. No oil or power steering coolers. On the anti freeze side it does have a heat exchanger in the water heater and a small heater in the cabin.......D......
 
Sounds
Ike you're assuming you down to 50/50. Looks like you've ruled out any obstructions. You don't have much else left.
 
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