Overheating 1 408

[stbtack1]

I know this subject has been covered from a couple of angles but I need some advice. Running at 1800 I can stay at or near 180. Anything more and she starts to overheat. Back it down and she will drop back to 180ish. Thus far I have checked the strainer which was not fouled, checked the raw water pump and it seems to be functioning ( I get a stream of about the diameter of my pinky maybe a little larger) so I turned my attention to the HX and the fresh water system. Just before I pulled the HX I checked the antifreeze in the expansion tank and noticed a thin layer of gel at the bottom of the tank. The color was yellow not brown or red so I don't think it was a result of mixing ethyl glycol with dex. My gut is telling me this could be the source of the problem. So I assume a antifreeze flush is in order, what is the best product and process? I also assume it would better to do the flush and then pull the HX? Maybe the flush will allow me to avoid pulling the HX? Also has anyone upsized their HX?

[SVJourney]

You should be getting more water than that. 

First I would pull my raw water pump cover and replace the impeller if you have not done so in the last year.
If you don't notice an improvement, then remove your cooler and take it to an automobile radiator shop and have it boiled out.  You may have clogged tubes or old zincs or something blocking the passages.
As far as flushing the freshwater circuit, you shouldn't have to use caustics as the passages are large.  Just running some water through, draining,  then filling with coolant should be okay.  I only know of one other 4-108 person who had to tear down their engine because it had been run forever without changing coolant.

[stbtack1]

So the issues of restricted flow on the raw water side of the HX don't appear on the freshwater side of the HX?
?

[SVJourney]

Not normally.  Unless your coolant looks like brown sludge, the freshwater side doesn't normally have an impact as long as the thermostat works as it should.  (you can get the thermostat at any autoparts store and save $$ BTW) I have heard from one person who couldn't get their freshwater side to work,  but the raw water side or the cooler is much more problematic and I would start there first.

The raw water side has lots of ions that flow through it that can clog stuff off.  You can check it this way:  Pull the hose running to your cooler and start the engine.  The water should come out with the force of a garden hose. If not, check to be sure that all the vanes on the impeller are still there.  Better yet, replace it as long as you have the cover off (cause you do that every year or so anyways right?) If any vane is missing it might be stuck somewhere down the line choking off your water flow. Then check your inlet suction hose to the pump to make sure its not collapsing from the suction somewhere.
Reattach the cooler inlet hose and remove the hose from the outlet of the cooler, should be the same amount of flow. If not, then get your cooler repaired.
The last place that would likely impair raw water flow is the exhaust elbow. 

[stbtack1]

Great info thanks

[stbtack1]

Pulled the HX among other things the raw water outflow side was 50% clogged with scale and zinc remains. There is a rattle in the zinc side so I am guessing those are remanents of zinks past. To the radiator shop.