12V 5.9 Cummins Diesel Coolant

[JHZR2]

I’m buying a 96 Dodge Ram Cummins, which has good service records. It currently has “green” coolant in it. While I’ll know when it was done last, no guarantees on what it was.
System looks great, coolant is clean, but again I’m not entirely sure what it is.

I currently keep G-05, G-48, JD Cool-Gard II, Honda premix, and some Dex cool. Dex goes in my Chevy truck, G-48 in my 135i. I’m not inclined to run either of those. Doubt Honda is the right stuff for a fully iron diesel.

G-05 is a well known quantity that I run in my iron MB diesels. JD is good stuff and I’d be confident running it.

I don’t know if the green in there is something like the Zerex traditional silicated green, or something like prestone all makes with cor guard. Due to the unknowns Id do a couple drain and refills with distilled water, just driving enough to warm the engine and mix fluids. Then I’d introduce the new coolant.

So what should I run?

 

[Trav]

If it were easy to remove the thermostat and a heater hose I would remove it and flush the block and heater core out, remove the lower radiator hose and flush it out. Blow it out with compressed air (about 20 psi is okay use a rag around the blow gun to seal it off) from where the thermostat goes that should get a good amount of the water out.
Reinstall the thermostat and vacuum fill it with JD. If you have premix you may have to drain and fill the radiator once it has been running to get the freezing/boiling point where you need it.

It probably has block drains but just because I am in salt belt I am a bit leery of trying to crack them open so I do it this way.

 

[naterbomb]

If it were easy to remove the thermostat and a heater hose I would remove it and flush the block and heater core out, remove the lower radiator hose and flush it out. Blow it out with compressed air (about 20 psi is okay use a rag around the blow gun to seal it off) from where the thermostat goes that should get a good amount of the water out.
Reinstall the thermostat and vacuum fill it with JD. If you have premix you may have to drain and fill the radiator once it has been running to get the freezing/boiling point where you need it.

It probably has block drains but just because I am in salt belt I am a bit leery of trying to crack them open so I do it this way.

I 2nd this. Drain and flush and fill with JD Cool-Guard II

 

[Chris142]

It probably has block drains but just because I am in salt belt I am a bit leery of trying to crack them open so I do it this way.

No block drains.

 

[JHZR2]

If it were easy to remove the thermostat and a heater hose I would remove it and flush the block and heater core out, remove the lower radiator hose and flush it out. Blow it out with compressed air (about 20 psi is okay use a rag around the blow gun to seal it off) from where the thermostat goes that should get a good amount of the water out.
Reinstall the thermostat and vacuum fill it with JD. If you have premix you may have to drain and fill the radiator once it has been running to get the freezing/boiling point where you need it.

It probably has block drains but just because I am in salt belt I am a bit leery of trying to crack them open so I do it this way.

Im waiting on records. I need to determine if the killer dowel pin has been remediated. If not, I’ll pull the front timing cover and will be removing all that anyway.

the system is something like 26qts so it’s a lot of fluid. I have a vacuum filler though so that helps.
Probably good to replace hoses and water pump (and belt and tensioner) while at all this. Even if fairly recent.
Thanks!

 

[nthach]

I’d go with JD Cool-Guard. Diesel engines need a greater degree of cavitation control. G-05 can hold up in a diesel - no pesky EGR cooler on that Cummins. John Deere did use G-05 as well.
Zerex says G-48 can be used in heavy-duty diesel. It’s a 2-EHA SiHOAT. It seems like Detroit Diesel, Volvo Truck/Bus and a few other heavy duty OEs approve it.

Prestone now sells a new HD Cor-Guard. Supposedly it’s nitrite and 2-EHA free.

US_Val_ZXG48_AFC_HD_EN.pdf - DocuSign CLM

sharena21.springcm.com

 

[thastinger]

Ditto for cool guard in a wet sleeve diesel. Will probably take more than a few fresh water flushes to get the green stuff all the way out.

 

[ofelas]

Don't need no stinkin' SCAs in a 5.9 Cummingsz.

MS-9769 (HOAT/G-05) & done.

 

[bullwinkle]

Parent bore engine, no sleeves. Any green or G-05 (if you want to go more than 3-4 years on it) would work fine. Unlike the 7.3 IDI in my sig, it's got to have SCAs, green coolant, and (preferably) a coolant filter to catch the excess silicate (from the SCAs and coolant).

 

[JHZR2]

I went with JD Cool Gard II long ago. Starting to exchange what was in there was one of the first things I did when I got the truck.

I’ve done a full hoses off flush, and another exchange of just the radiator. Looks great and works perfect in all conditions. I don’t tow, but I do haul near gvwr/payload rating.

This was the last time I did a drain and fill of the radiator. Good color, very clear. I hadn’t topped it up yet. Obviously lots of scale in there but doesn’t seem to affect much.

 

[ofelas]

You still running the factory 180f stat?

 

[JHZR2]

You still running the factory 180f stat?

Yes. Ive seen that there is a different one from, I think it was the old Chrysler 440 engine, which fits and is higher temperature... maybe worth a swap some day. But the thermostat in there works fine.

I know some claim their trucks cycle all the time. Mine only did when I partially blocked the radiator. It’s pretty steady otherwise... which is why I’m tempted to keep it.

 

[ofelas]

I run a 190 stat, steady needle after the stat opening initial swing.

I like the more consistent cab heat & the warmer oil temperature.

Yes, 440 stat, or a NAPA #532090 both 195f for your application.

 

[bullwinkle]

I went with JD Cool Gard II long ago. Starting to exchange what was in there was one of the first things I did when I got the truck.

I’ve done a full hoses off flush, and another exchange of just the radiator. Looks great and works perfect in all conditions. I don’t tow, but I do haul near gvwr/payload rating.

This was the last time I did a drain and fill of the radiator. Good color, very clear. I hadn’t topped it up yet. Obviously lots of scale in there but doesn’t seem to affect much.

View attachment 51620

That looks like a good citric acid flush, or even boil out the radiator candidate. Typical for running green too long, or with non-distilled water. You should have seen the F-450 when I bought it...

 

[Chris142]

If it were easy to remove the thermostat and a heater hose I would remove it and flush the block and heater core out, remove the lower radiator hose and flush it out. Blow it out with compressed air (about 20 psi is okay use a rag around the blow gun to seal it off) from where the thermostat goes that should get a good amount of the water out.
Reinstall the thermostat and vacuum fill it with JD. If you have premix you may have to drain and fill the radiator once it has been running to get the freezing/boiling point where you need it.

It probably has block drains but just because I am in salt belt I am a bit leery of trying to crack them open so I do it this way.

Zero block drains on a 5.9 Cummins

 

[JHZR2]

That looks like a good citric acid flush, or even boil out the radiator candidate. Typical for running green too long, or with non-distilled water. You should have seen the F-450 when I bought it...

I had thought about citric acid. Have used it quite well on my old MB diesels. This is a big radiator and I’m not sure how great of condition it is, at its mileage, so aim sticking with “ain’t broke”, since it works really well, temperatures are stable even in high heat, and it works for the hauling I do.

 

[totegoat]

Hard to beat Fleetguard ELC.

 

[ofelas]

JHZR2 -

Makes sense, unless you find a good shop to rod out the rad.

You'll likely get a more efficient front stack by degreasing the rad/IC/condenser fins regardless of rad core service.

Couple other things I will suggest for the next time you change the coolant/stat -

Flip the inlet/outlet hoses on your heater core tubes.

Dump 8oz of RMI-25 into the rad; I'm not a believer in most additives, but along with Lubegard Red pack in the ATF, RMI-25 flat out works.
I've used it in price challenged & neglected cooling systems, it safely floats junk to the top of the overflow bottle/and generally has heat pumping out of the core in relatively short order.

I had thought about citric acid. Have used it quite well on my old MB diesels. This is a big radiator and I’m not sure how great of condition it is, at its mileage, so aim sticking with “ain’t broke”, since it works really well, temperatures are stable even in high heat, and it works for the hauling I do.

 

[JHZR2]

JHZR2 -

Makes sense, unless you find a good shop to rod out the rad.

You'll likely get a more efficient front stack by degreasing the rad/IC/condenser fins regardless of rad core service.

Couple other things I will suggest for the next time you change the coolant/stat -

Flip the inlet/outlet hoses on your heater core tubes.

Dump 8oz of RMI-25 into the rad; I'm not a believer in most additives, but along with Lubegard Red pack in the ATF, RMI-25 flat out works.
I've used it in price challenged & neglected cooling systems, it safely floats junk to the top of the overflow bottle/and generally has heat pumping out of the core in relatively short order.

Ive got both products in stock. Fine points and will do. I am planning to do an AT service soon, maybe a few upgrades... and RMI-25, very easy to do...

Heat works great! As does AC!

 

[Creekside]

If you have the JD Coolgard that would be my pick 100% of the ones you listed. If it were mine I would use TRP coolant. That's what I use in almost everything. It is available from your local Peterbilt or Kenworth dealer. Also available from your Cat dealer just under their own name. Fleetcharge and Finalcharge are great as well it just depends on how much maintenance you plan to do. The TRP is similar to Finalcharge.