‘Best’ Antifreeze/Coolant Type in 2023? Green IAT? Change to OAT? Experience/Advice? (Page 1/3)
Vintage-Nut APR 16, 07:33 PM
Antifreeze has changed a lot over the decades after the birth of the Fiero, and you guys know way more about antifreeze/coolant than I ever will learn ….

In early of the 21st century, many members were posting that they still use the traditional bright green stuff (GM 1825M spec / IAT) as the ‘best’ antifreeze.

Traditional Green IAT is fast-acting and protects cast iron engine blocks and copper/brass heater cores from corrosion; but IAT needs frequent changes (two years OR every 30k miles) as silicate causes scale in aluminum radiators and phosphate dries/corrodes rubber. Most manufacturers stopped using it by the mid-1990s.

GM 1825-M / 6043-M Spec – Inactive / 2nd - GM 6038M / 1899M Spec – Inactive / 3rd - GM 6277M Spec – Inactive

GMW 3420 is the most current spec as Active (2017) which is Organic Acid Technology (OAT) - ethylene glycol based ‘extended life engine coolant’ with a maximum recommended service interval of ten years (or 150,000 miles).

OAT is either silicate free, phosphate free, or both and are slower acting but much longer-lived than IAT antifreezes. OAT corrosion inhibitors provide excellent long-term protection for aluminum and cast iron, but may not be the best choice for older cooling systems that have copper/brass heater cores.

GM OAT-based Dex-Cool which is dyed orange (which has only a few PFF threads)
Prestone OAT-based “All Vehicles” which is dyed bright yellow
There are green, blue, red, even pink OATs’!


However, I didn’t find current threads (2018 or newer) in the PFF system about the ‘best’ antifreeze type for the present day; i.e. year 2023.

I believe more members are using OAT these days, but I know that my ‘classic truck’ buddies are still using IAT.

This has created some confusion as the type of antifreeze in my ‘88 Fiero…..

Do you still use the traditional green IAT antifreeze in your Fiero?

Did you change to OAT antifreeze?

I’m leaning towards to fill the GT with Prestone OAT-based “All Vehicles” antifreeze however; I wanted to hear from the Fiero ‘gods’ on the forum…..


And YES, I studied and learned the antifreeze/coolant contamination 101:
*Don’t mix antifreeze/coolant technologies - NEVER
*When in doubt, thoroughly flush and purge it out!

The cooling system fluid capacity of the 2.8L engine is 13.8 quarts; when draining it for the first time, it will measure approximately 7 quarts which means ~50% of the old coolant is ‘trapped’ in the system.

The complexity of cleaning out ALL the old coolant requires many flushing’s until the drained liquid is nearly colorless.

The completely flushed coolant system has ~7 quarts of ‘water’ in the engine block and ‘water quality’ matters! I always use distilled water…

After that, full strength concentrate antifreeze is use to fill the coolant system and the clean recovery tank.
VN
olejoedad APR 17, 10:42 AM
The Universal yellow coolant works well.

The coolant/water ratio should be 50/50.
sleek fiero APR 17, 11:43 AM
When flushing out the cooling system remove the two 1/4 " drain plugs out of the block so the sludge gets flushed out of the low areas around the cylinders. this will get rid of most of the remaining liquid. also drain the coolant pipes with the plugs in front of the rear wheels, coolant catch tank and bottom of rad. If you disconnect heater line at the engine fill you can blow out the heater core and lines. Now you have a clean liquid free system to refill with longlife 50/50. sleek
theogre APR 17, 01:35 PM
⚠️ Warning: Do Not use DexCool in cars that have/had Green or other types. GM Never claim DexCool is "better" except in new cars that use it right from the factory. Even factory installed DexCool systems has/had problems.

"Best" now is "universal" coolant often Yellow color from several brand that mix w/ or replace other coolant products.
Can still get Green coolant but not sold at most retailers now. Some brands don't even offer Retail Packages of "Old" Green now.
Example: Prestone has "Asian" coolant that's Green but likely not same formula as old Silicates Green.

Do Not use 50/50 mix after flushing. Use straight coolant then add water and let car mix them.
See https://web.archive.org/web...cast.net/~fierocave/ coolant fill.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

sleek fiero APR 17, 03:12 PM
AS long as its properly flushed Dexcool is fine. I checked with both of our GM dealers in town and both said no problem. They don't use anything but dexcool even on their older trade ins. I have been using dexcool for 30 years now and have NEVER had a problem .
Vintage-Nut APR 17, 07:11 PM
Thanks - I'll use "universal" Prestone OAT-based “All Vehicles” antifreeze which is bright yellow.

When it is time to flush my '84 Chevy, maybe I'll change to OAT too so all of my pre-2000 vehicles will be using the same antifreeze.....

Thanks again for confirming,
VN
theogre APR 17, 08:33 PM

quote
Originally posted by sleek fiero:
AS long as its properly flushed Dexcool is fine. I checked with both of our GM dealers in town and both said no problem. They don't use anything but dexcool even on their older trade ins. I have been using dexcool for 30 years now and have NEVER had a problem .

You maybe just got lucky. The Dealers are 100% Wrong.

GM Corp has Many Doc's saying that is wrong. Including Many TSB that many Dealers Ignore.

GM also stated many times installing DexCool in vehicles that had Silicates or other Reduces DexCool to 3 years 30,000 miles.
If others are added to Factory DexCool system get same service interval drop.
DexCool is famous for plugging the system even on Factory install coolant.
sleek fiero APR 17, 10:10 PM
Mr. Ogre ; I am not out to get in a pissing match with you. You can use what you want but there is nothing wrong with Dexcool, Prestone Dex-cool or fords blue version of dexcool. you just cannot run a lead soldered copper rad with it.. it is meant for aluminum or aluminum with plastic tank radiators. As long as the system is flushed well it will perform well.
theogre APR 17, 11:45 PM

quote
Originally posted by sleek fiero:
Mr. Ogre ; I am not out to get in a pissing match with you. You can use what you want but there is nothing wrong with Dexcool, Prestone Dex-cool or fords blue version of dexcool. you just cannot run a lead soldered copper rad with it.. it is meant for aluminum or aluminum with plastic tank radiators. As long as the system is flushed well it will perform well.

All Fiero and a lot of others have Brass/Copper Heater Cores with Lead base solder.
Only those vehicle had the cores replace since Manufacturers comply w/ RoHS maybe have non-lead solder. Old Lead solder replacement cores where still in inventory many years after RoHS and Anti-lead laws/rule. Can still find NOS, used and repaired/rebuild with lead solder.
Non-lead solders often have problems on their own w/ or w/o DexCool.
sleek fiero APR 18, 12:00 AM
You are right. Thinking about it I changed out my heater core when I got my GT 29 years ago. I guess that's why I have never had a problem with dexcool. Jeez I guess I better drain it out of my 88 Vette too-------NOT.