Change from Dexcool OAT to HOAT?

Joined
Apr 30, 2017
Messages
137
Location
Michigan
I had major work done to my 1966 Mustang powertrain; Basically engine rebuild, new radiator, heater core, hoses, etc. The shop filled it with a Dexcool OAT Havoline orange colored coolant when I asked for the IAT older type green. Why did I want the older IAT type? Well I had heard and read a lot of bad things about Dexcool and all OAT coolants in systems not designed for them, and I figured that the safest bet would be the old-style green the car was engineered for. So now what do you all recommend? 1. Just stick with the Dexcool and don't worry about it? 2. Flush it out as best as I can and go with green and take a chance that not all of Dexcool is out of the system? Take a risk that it would congeal into jello? 3. Take a middle of the road approach and put in a HOAT coolant which seems to be compatible with both the green IAT and the OAT/Dexcool coolants if not all of it is flushed out? Minimize the risk of congealing but maybe not eliminate it?

The car is driven sparingly. To shows, Cars & Coffees, on nice weekends and it is stored over the winter (December through March)
 

JRed

Site Donor 2021
Joined
Jun 1, 2009
Messages
2,590
Location
Virginia
I'd flush it all out thoroughly with distilled water until it runs clear when you dump it and put whatever coolant you intended to run it. I wouldn't mix anything with dexcool, compatible or not.

For what it's worth I'm with you on the "Please no dexcool". I've had multiple family members get burned by late 90's/early 2000s GM vehicles with DeathCool to the point that if they buy an older GM we always flush the cooling system and put conventional green in them.
 
Joined
Mar 2, 2013
Messages
8,795
Location
The Midwest
Dumb shop. Zerex original green from Napa is a safe choice after a complete flush. But I myself would research a longer lasting coolant.
I'd be the oddball using Zerex G40 which is a Si-OAT coolant.
 
Joined
Apr 27, 2010
Messages
8,765
Location
Suburban Washington DC
Why did I want the older IAT type? Well I had heard and read a lot of bad things about Dexcool and all OAT coolants in systems not designed for them, and I figured that the safest bet would be the old-style green the car was engineered for.
The negative stand on Dexcool has been debunked years ago. And if your car was engineered for SC grade motor oil, so would you use that as well on the next oil change?
 
Joined
Oct 9, 2004
Messages
11,508
Location
Cincinnati, OH, USA
I would be concerned about the other work done to the car if they were stupid enough to put Dexcool in something that old! One possibility that won't cause trouble is the newer Prestone AMAM with (or without) Cor-Guard-I have a mix of Specialty Orange, new Prestone Dex-Cool, new Prestone AMAM. and used Dexcool in the Transit 250, it's a nice weird shade of darker red, but it hasn't had any problems with coolant.
 
Joined
Oct 9, 2004
Messages
11,508
Location
Cincinnati, OH, USA
The negative stand on Dexcool has been debunked years ago. And if your car was engineered for SC grade motor oil, so would you use that as well on the next oil change?
Ford is having issues with Orange (which is Dexcool) in their NEWER vehicles and is changing them all to Yellow (which is Prestone AMAM)-on an older car, which has had IAT green it's entire 55 year life, there's bound to be something left in the cooling system that won't play well with Dex, and it's an open expansion tankless system, another Dex minus, there will be air present in the top tank of the radiator-not good.
 
Joined
Oct 13, 2008
Messages
14,840
Location
The Old North State
With several distilled water radiator d&fs you should be able to get the system clear or very close. Original spec would be an Original Green IAT. So then you could use a concentrated version of one OG like Zerex or another. Another option, go with full strength G-05 (HOAT), readily available, reasonable priced. I think either would work fine though specifically Zerex OG can be tougher to find. G-05 nice service interval too.

Personally if my car and shop used Dex, I'd want it out of topic vehicle.
 

CKN

Joined
Oct 14, 2014
Messages
7,159
Location
Utah
I'd flush it all out thoroughly with distilled water until it runs clear when you dump it and put whatever coolant you intended to run it. I wouldn't mix anything with dexcool, compatible or not.

For what it's worth I'm with you on the "Please no dexcool". I've had multiple family members get burned by late 90's/early 2000s GM vehicles with DeathCool to the point that if they buy an older GM we always flush the cooling system and put conventional green in them.
Key words and why they are meaningless now.....................
 
Joined
Jan 3, 2020
Messages
474
Location
YYC
You'll be fine with the Dex-cool. There's millions of old cars rolling around in the US with Dex-cool or a Dexclone that are supposed to have some older formula and they're perfectly fine. A lot of people rebuild classic American V8 vehicles and run Dex-cool or a Dexclone with no issues.
 
Joined
Jun 3, 2002
Messages
8,324
Location
MI
Building3

Just to make your decision more difficult, here is a VERY old article that "suggests" that the conventional IAT type coolant might work better protecting old school materials used in very old vehicles (brass, copper, solder, maybe iron).


The problem with all of this is that we have no coolant experts here and everything is anecdotal. Today's low silicate level of the Zerex green is approximately the same as their G05, so that should be a non issue. My layperson, non-expert choice based on old man bias would be green IAT coolant and maybe G05 if I studied up on it a bit more. Why? Because all of the semi-older coolant charts recommend green coolant for old vehicles. https://www.google.com/search?q=coolant+charts&client=firefox-b-1-d&tbm=isch&source=iu&ictx=1&fir=lGxDip8hoNrpHM%2Cj3TbpzWXxqum7M%2C_&vet=1&usg=AI4_-kT4B39tANxIT7-OuovZssg_RvOCyQ&sa=X&ved=2ahUKEwjpxLeNtvzvAhWbAZ0JHUOOApAQ9QF6BAgWEAE&biw=1920&bih=966#imgrc=0Et8ZvUo_86nyM

Good luck on your decision.
 
Last edited:

JHZR2

Staff member
Joined
Dec 14, 2002
Messages
46,995
Location
New Jersey
Nothing wrong with dex in a system well maintained and/or designed for it. I’ve had no issues with system cleanliness in my 98 Chevy which was not designed for it, but got it from the factory.


Since it’s likely your system is as clean as it will get, it’s a fine time to change to OAT if you’re in control.

That said, for my dollar in that car, I’d be running John Deere Cool Gard II.
 
Joined
Jan 18, 2020
Messages
1,890
Location
United States
Where did you hear this ?
speciality orange (dexcool) was having trouble with the heater cores in the transit, supposedly leaving deposits that inhibited heater performance. prestone is the current supplier of ford’s orange and they introduced their next gen long-life POAT formula to mitigate this problem.

Dexcool has been used by FoMoCo for 25 years, it has been a very effective and very long lived coolant.
 
Last edited:
Joined
Oct 13, 2008
Messages
14,840
Location
The Old North State
"Dexcool has been used by FoMoCo for 25 years,"

I've seen no evidence to confirm that statement. Linked is the Motorcraft AF chart showing all AF recommendations for their 'US based vehicles", including topic vehicle. Note Dexcool orange doesn't show up until 2/2010 and then FoMoCo decided they would back spec the new DY yellow for the Dex Orange. Something as the chart shows they never done in the past. Also while the newer DY yellow contains some P it is not a true Asian PHoat because like Dex it uses 2eha as inhibitor.

Motocraft Antifreeze/Coolant-Usage chart

The back spec to the newer DY yellow could indicate FoMoCo lack of trust in Dex Orange and yellow DY having a lower concentration 2eha.
 
Joined
Jan 18, 2020
Messages
1,890
Location
United States
"Dexcool has been used by FoMoCo for 25 years,"

I've seen no evidence to confirm that statement. Linked is the Motorcraft AF chart showing all AF recommendations for their 'US based vehicles", including topic vehicle. Note Dexcool orange doesn't show up until 2/2010 and then FoMoCo decided they would back spec the new DY yellow for the Dex Orange. Something as the chart shows they never done in the past. Also while the newer DY yellow contains some P it is not a true Asian PHoat because like Dex it uses 2eha as inhibitor.

Motocraft Antifreeze/Coolant-Usage chart

The back spec to the newer DY yellow could indicate FoMoCo lack of trust in Dex Orange and yellow DY having a lower concentration 2eha.
B1E58F92-7860-4826-91A6-D9724BEE286F.jpeg



WSS-M97B44-D predates WSS-M97-B51A by several years. Ford of Europe and Australia and all other global operations totally transitioned to orange by 1999.

Back speccing yellow allows them to consolidate inventory, speciality green is also being phased out for that reason. Millions upon millions of Ford vehicles have been filled with orange without issue over the past two decades
 
Last edited:
Joined
Oct 13, 2008
Messages
14,840
Location
The Old North State
^^^Congrats you found the singular anecdote of one vehicle, in 1999-02 Cougar not made in the US. Specifically why I used the term "US based" meaning manufactured FoMoCo vehicles. And since being exacting, it's not "25 years" as stated.

Back to topic, OP vehicle is not a 99-02 Cougar, specing Dexcool. It's a 1966 Mustang originally using IAT green, so still irrelevant to topic.

As for back spec of DY yellow, still doesn't explain why FoMoCo feels the need to allow supersession of Orange Dexcool with DY yellow. Or why using chart it appears FoMoCo now moving away from Orange Dexcool use.
 
Last edited:

Building3

Thread starter
Joined
Apr 30, 2017
Messages
137
Location
Michigan
Thank you to everyone for your time to reply. As I see, it is a complicated issue with lots of opinions and real world experiences. So my choices seem to be: keep the orange Dexcool, or use Zerex Original Green, Zerex G40 Si-OAT, G-05 HOAT, Prestone Yellow. From the reading I have done, and your inputs, it seems like the old-style Green was a fast acting antifreeze/coolant and that is why it needed to be changed every 2-3 years, while the newer OAT takes much long to be effective (the attached article said thousands of miles.) Well, I am talking about a 1966 Mustang that is only driven several hundreds of miles a year, so for that reason I am hesitant to keep it in the system. Plus it was not designed for it as far as fluid flow and materials. It seems like many of the Dexcool problems have been with systems not designed for it. So then it's down to how certain I am that every drop of Dexcool can come out of every nook and cranny in the engine, radiator, heater core, hoses, etc. in order to prevent the "jelling" of the coolant. Do I take the risk of going all the way back to green? or a safer bet and use HOAT which seems like a reasonable compromise? I see that the Zerex OG is actually available in a 5 year formula. That's nice since it reduces the maintenance for a car that is not driven much. Any other thoughts? Thanks again.
 
Joined
Jan 18, 2020
Messages
1,890
Location
United States
Thank you to everyone for your time to reply. As I see, it is a complicated issue with lots of opinions and real world experiences. So my choices seem to be: keep the orange Dexcool, or use Zerex Original Green, Zerex G40 Si-OAT, G-05 HOAT, Prestone Yellow.
gelling will not happen unless you deliberately find a very old IAT formula and introduce air into the system.

original green is a garbage low silicate IAT, do not use it in anything. if you’re afraid of a modern coolant attacking solder, use G05, which happens to reboxed in europe as Glysantin Classic antifreeze.
 
Last edited:
Joined
Jan 18, 2020
Messages
1,890
Location
United States
Or why using chart it appears FoMoCo now moving away from Orange Dexcool use.
because it’s a decades old coolant formulation and their supplier has a longer life and fully compatible product on the market?
 
Last edited:
Top