Perkins 4-108 overheat

[captchetco]

I have owned and used "Someday" since 1983, extensively since 2005 after retirement. I have made many trips up and down the coasts of Oregon and Washington, and the large rivers. The engine never overheated, either before or after its total rebuild. I had run it at full speed, 2750 RPM (even though rated at 3600 RPM max, but its speed does not increase, even slows at max RPM attainable of 3200.). It has been run hard many of times, 2750 or a bit more for hours entering the Columbia River, and out running weather.
Never overheated, usual temp 185. Took a year off and sailed from Oregon to Puerto Vallarta in 1996. Noticed it ran at higher temps south, to 200 deg.


Before returning south after retirement in 2005, I made several changes, all oriented to improving cooling somewhat. Off the PNW, it wouldn't quite reach 185, which was the thermostat, after the changes.

However, now, at cruise RPM of 2400, it runs at 200-205, whether I have the 185deg thermostat in or out. At 2750, it will overheat in less than 1/2 hour. Several times I have changed the guage, both mechanical and electric, and a handheld infra red.

I clean the RW strainer, and Heat Exchanger before each departure. The impeller is renewed frequently, alternator belt is tightened regularly, I have changed coolant types several times, but currently it is "green" mixed 50-50 with distilled water, which is clear green. I have lowered the lift muffler 2", all that is safe. There is good water flow. My last trick is adding an additional transmission heat exchanger, RW to trans fluid. That has helped, and trans temp is now down to 150, but engine still running appx 200, but in a one hour test at 2750, engine showed 215, but didn't boil with the 7# pressure cap. I am not too concerned about running at 200, but I may need the last one knot per hour at 2750, without fear of overheating.

What am I overlooking or not considering? Is it the 80deg raw ocean water? or what? Anything I can do tofurther improve cooling?

[CSY Man]

Had the same problem on my 4-108. (Plenty of old threads about these engines overheating)
My cruise RPM was 70% of max continuous, or 2100 at which it never went above 185.
Above it 2450 it would slowly run hot and at 2800 it would overheat fairly fast.
I tried lots of stuff as well, including prop pitch changes, but finally concluded I needed a bigger heat exchanger: Never got around to it as the temperatures were normal at my cruise RPM.

[rbk]

Next thing I’d be checking is the mixing elbow for buildup.

[Lepke]

Be sure your gauge is accurate.

If you haven't done a flush with a descaler that dissolves rust, do that next. Rust will build in the water passages and acts as insulation, restricting the coolant's ability to draw heat out of the head and cylinders. For some reason many people don't think to clean the coolant side. I've fixed heating problems other couldn't just by doing a proper coolant flush.

Many people have put bigger heat exchangers on 4108s. The commercial rating is 3000 rpm and the engine should run at that rpm and 40 hp output just about forever.

[captchetco]

I have changed the temp gauges from electric to mechanical and back and changed sensor locations, but the result is nearly identical.

Re: the suggestion of flushing. The block was boiled out at rebuild. I always have coolant and distilled water in it, and when changing, flush with dock water pressure. Perhaps that is not enough. I recently was suggested "Hammerhead" flush which I could not find in Mex. Has anyone had experience with this?

Since it is a High lift muffler, the mix is within the muffler...No elbow. I did have the muffler disassembled in Panama, inspected and cleaned. No change.
Perhaps the "bigger heat exchanger" is the logical next step. I did increase the flow by changing all the plumbing components except the strainer itself from 3/4" to 1". More visible exhaust water, but no change in cooling.

Thanks for the good replies.

[rbk]

Possible you could have dislodged a large chunk is something that is now restricting flow outside of the HX? It sounds like a larger HXis a bandaid, might do the trick but shouldn’t be the answer. Something else going on

[captchetco]

Before I realized that impellers weren't similar to good wine, and didn't improve with age, I had a few disintegrate. The pieces always ended up in the input end of the FW side of the heat exchanger. I do not have any impellers missing teeth, nor now any pieces at the in end of the HX. I do clean the HX tubes very often.

To clairify, There are actually 3 HX on the engine, and now a 4th which is remote. 1, is the Raw water to coolant, which is the one we have been discussing. There is also a unit on the side of the engine which has two separate tubes, One tube is engine lubricating oil, the other is transmission oil, around which coolant circulates right after leaving the water to water HX. The fourth is the one I have added to the trans oil which is in sequence to the one on the side of the engine, and cools with raw water. It has done some good since I added it.

[captchetco]

Is it possible the injection pump is slightly out of time? In old cars, if the spark was retarded, they would run hotter. If this is possible, which way would I tweak the injection pump, and by how much? There isn't any timing mark except that on the pump and mount, and they match.

[stormalong]

First thing to try is to clean the tube stack.

Get a piece of PVC pipe a little wider and longer that the tube stack. Glue a cap on one end. Soak the tube stack in white vinegar overnight. Rinse it with fresh water and take note of how much crud comes out.

The buildup happens over a decade or more and regardless of how clean the freshwater side of your cooling system the buildup on the raw water side slows the heat transfer process.

I have done this on my 4-108 and it's replacement and the results are remarkable.

[captchetco]

I am not understanding what the "tube stack " is. If you mean the tubes that are in the HX, I clean those before every departure by pushing a soft brass rod through each tube. I also have on occasion removed the entire unit, sweated the end off and boiled it out with vinegar. Is that what you have in mind?

[stormalong]

Originally Posted by captchetco

I am not understanding what the "tube stack " is. If you mean the tubes that are in the HX, I clean those before every departure by pushing a soft brass rod through each tube. I also have on occasion removed the entire unit, sweated the end off and boiled it out with vinegar. Is that what you have in mind?

Yes, That is exactly what I am saying. I do not understand your meaning of sweating the end off. Do you have the "lowboy" version with the Bowman heat exchanger or the older version?