4D55 Water Temperature Question

[Sandrailstudent]

I have an 85 4D55 that only has 110k miles on it, which is great. Unfortunately, it ate a head gasket on the last owner when he got it at 100k, and I just had to replace one.

I have flushed the coolant system with a cleaner, and flushed it a ton. I am filtering the coolant at the outlet of the engine and at the bypass to the heater. I kept getting peegravel sized iron chunks coming out for the first few hundred miles, but now it is just a very fine dust that paper filters catch. I think that the head gasket blew out because of a lack of coolant flow, especially through the head. I als don’t know if the warmer temperature contributed. I am asking for what is “normal” as I try to raid the coolant temperature in order to get the right powe and fuel economy.

I have a 160F thermostat installed with 4 little holes drilled in it, one of which is factory. The temp gauge only comes to 1/4 to 3/8 up from the bottom, and the water to the radiator only measures 130F from an IR gun. Is this where it should be????

Before the head gasket blew out, I had installed a 160F thermostat with no holes. The temp gage came up quickly to 1/2, exactly in the middle and didn’t fluctuate.

I also switched to Peak Final Charge coolant in order to eliminate any possible cavitation on the outside of the wet cylinders. I still don’t think that it is normal to get a fine dust from the coolant, but I never looked this closely.

Any help or advice would be appreciated.

thanks, Chris

[Melkor]

i would be adding some CLR to plain water and running it for a few days like that, it will help break down any rust or blockages in the system

[Sandrailstudent]

For anyone bored, or curious, I found the "official" answer in the 4D55 Cooling System Shop Manual to be 82°C (180°F) to start opening and 95°C (203°F) for full opening with an 8mm gap. If i am staying under 203F, then the cooling system is in the controlled range, and the Tstat is still throttling the cooling system.

The multi-vehicle encyclopedia that I bought for everything Mitsubishi made in the 80's and 90's had 190°F, but I never put anything that high in. The thermostat that I have in it now is 180F, and am monitoring temperatures. So far it is staying pretty consistent. I replaced the Tstat with extra holes in it so the motor will actually warm up in a reasonable timeframe of 5-6 minutes of driving instead of creeping up over 20 minutes.

Since posting I talked with Mike Warme, who was an absolute WEALTH of knowledge. He recommended that I get the radiator professionally cleaned at a radiator shop, which I did. They had to clear the passages with rods as the boil didn't clear it out. I also changed out ALL of the radiator/heater hoses to avoid any rubber fines in the system.

All that said, it should have a much better chance at staying cool and keeping a head gasket alive. I am still filtering the coolant, and the amount of iron/copper/rubber is still slowly dissipating. I am also using Peak Final Charge diesel coolant so that any possible cavitation is minimized from here on out. IDK if that is a problem with these motors, but it is a risk that i'm mitigating.

[Fingers]

Just as food for thought:
There is a product called Evans Coolant. It is waterless, so no corrosion. In semi trucks, this coolant would be matched with a MUCH higher thermostat (because diesels run better at higher temps) and a ZERO PSI radiator cap. Because it is waterless, it doesn't generate pressure. I won't get into it any further unless someone wants to bring up "overheating", then I suppose we can get into what happens during that process.

Side note: the boiling point of standard coolant is 226, Evans' boiling point is 375.

[Sandrailstudent]

Fingers, thanks for the suggestion. I looked up Evans and they use 74% to 90% ethylene glycol among other non-water chemicals. That seems like a good way to raise the boiling point. I was moving towards just using pure concentrated coolant, which would be higher viscosity than desired, but would get the higher boiling point of 388F (if I could get it completely free of water, which is unlikely). That is the cheap way to do it as Evans is at least 2x the cost.

The highest concentration that I have tried is 66%, which raised the boiling point to a modest 235F (at zero PSIG, which would be higher at 13-15 PSIG in a pressurized coolant system). At 95% it would be 317F, but I haven't been motivated to try that, either. The small amount of water difference from 95 to 100% glycol makes a huge difference in the boiling point (317 to 388F).

I'm sure that Evans is a better way to go than pure coolant concentrate because it is an engineered product and they have a way to get all of the water out. Both methods would do great at boiling, corrosion, and cavitation.

I am curious if anyone else has used Evans in these little trucks. I am pretty confident that I got my system cleared and my main cause of the head gasket failure solved, so the immediate need isn't there. Putting all of the other components up to higher temperatures doesn't seem like it would be good for their longevity, but since I've never tried I couldn't be sure. The rubber hoses would be my first concern, but the head and head gaskets would be my next.

[pennyman1]

There is no need to go that exotic with the 4D55. Running at the temps you are proposing may do more harm than good. It will be fine with the 180 - 195 thermostats - a reverse poppet tstat will do a better job with flow than drilling holes in the tstat. it opens with the flow instead of against it.

[Sandrailstudent]

Thanks for the feedback. I am not going to raise the boiling point much beyond the regular 50/50 coolant. The more I read and watch, having a boil over is not a bad way to get a warning that you have a problem. Of course, we should all see it on the gauge first, but we miss it sometimes.

For the record, I am done drilling holes in the Tstat. It took forever to warm up, and didn't get there most of the time. It was only a little better than running no tstat at all. I went those routes in order to make sure that I didn't have any sort of overheating condition that cost me another head gasket. I am new to 4D55's and diesels altogether, so I approached it conservatively.