GM/AC Delco Dexron HP information requested

[Stonecoldtx]

Hi, All--I'm new to this forum, but I am on many others around the Internet, and have been for decades.

I am currently intalling a Chevrolet Performance Connect and Cruise LT1\8L90E "E-Rod" into a 57 Chevy Sedan Delivery

For the transmission cooler, I will have a cooler in the radiator, and am using a DeRale 13960 External auxiliary cooler with fan

The DeRale specs state that the volume of this cooler is 16 FL OZ.; this, and the cooler in the radiator plus the lines are going to require some additional fluid to be added to the transmission--possibly as much as a quart after all is said and done, and I want to get it into the coolers and lines before I attempt to start the engine up . . .

In the Instructions that came with the Connect and Cruise kit, it states to ONLY use Dexron HP transmission fluid in the transmission, but after trying to find some and researching further, I found that Dexron HP apparently is no longer being produced, and has been superceded twice by other GM part numbers, the latest one seems to actually be Mobile 1 LV HP . . .

Since this engine/trans were built sometime in 2020, I need to know what fluid to use . . . do I need to go to a GM dealer and buy the latest Dexron HP part number, or can I use the Mobil 1 LV HP fluid, because the superceded part numbers occurred BEFORE this transmission was even built, so I have no idea what fluid was used to fill it originally . . .

Can someone please clarify which fluid I actually need?

Thanks in advance!

 

[redhat]

Yes, the Mobil 1 LV HP is what you will want to use. The original Dexron HP was made with an inadequate additive pack that resulted in shuddering in the 8L units. Others more up on this issue can chime in here and give a better explanation.

Get the Mobil 1 LV HP.

 

[MrHorspwer]

Mobil 1 LV HP is what you'll be looking for.

Also, for your cooler, I'm not sure how the 8L90 comes configured for Connect & Cruise, but if it has the OE thermostatic bypass valve, it won't flow any fluid to the cooler unit the trans is up to temp (something like 185F for 8L90 IIRC). Something to think about when you're topping up the fluid.

 

[blufeb95]

As long as what you have iis the blue label version of Mobil Synthetic ATF LV HP, if what you have is the black label version then do not use that.

 

[Stonecoldtx]

Thanks, guys--I have a couple of cases of the Mobil 1 LV HP stuff left over from when I had originally planned on putting a 4L60E behind the 350 that was in the car, before I switched over to the Connect and Cruise system.

As to the thermal bypass valve--it didn't come with one; this is what it says in the instructions about the adapter on the transmission:

Transmission Cooler Lines
The transmission is equipped with an adapter installed in the cooler line ports. This adapter has AN-6 fittings to facilitate cooler line installation. The adapter may be removed if production style lines are used. Do not remove the inserts. An adequate cooler must be used to ensure proper transmission operation

This is what the adapter looks like:

I plan on pumping fluid into both coolers and the lines with the lines detached from the transmission to get everything full, and then attach back to the transmission . . . I feel like this is a much easier proposition than trying to fill the transmission with the standard procedures, while laying on my back and the hot exhaust hovering just below . . . I've done that on 6R80 Mustangs, and that's no fun!

 

[AdmiralYoda]

I don't think that adapter has a thermostat in it...and that's fine. That means 100% of the transmission fluid goes to the external cooler before returning to the transmission. Considering the application (hot rod) you'll probably find that the fluid temperature will raise to 50-70F above ambient temperature after an extended period of use.

If you were after optimal fuel efficiency or cold weather use you might consider an adapter with a thermostat in it. It bypasses the cooler and recirculates the fluid back into transmission until it hits a defined temp. Much faster transmission fluid warm ups and sustained higher temperatures.

Improved Racing 8L90 Adapter

Also, Lokar makes a dipstick that fits the 8L90 too. You have to set full fluid level using the OEM procedure, then just scribe a line on the dipstick for the "full" mark.

I have the light duty 8L45 without a thermostat in it and an OEM external cooler. At 70F ambient it takes 45 minutes to stabilize to 135F. I've never seen it above 145F in 95F weather and stop and go traffic. If it is below freezing my transmission will barely crack 90 degrees. I plan to install the thermostatic adapter above just to maintain consistent temps through the seasons.

**EDIT.
I saw that you said that you have a few cases of LV stuff left over from a planned 4L60e install. The 4L60e uses Dexron III and was superseded by Dexron VI. It doesn't use Dexron ULV or HP LV. The HP LV is specific to the 8L and 10L transmission families. Double check what you've got there.

 

[Stonecoldtx]

I don't think that adapter has a thermostat in it...and that's fine. That means 100% of the transmission fluid goes to the external cooler before returning to the transmission. Considering the application (hot rod) you'll probably find that the fluid temperature will raise to 50-70F above ambient temperature after an extended period of use.

If you were after optimal fuel efficiency or cold weather use you might consider an adapter with a thermostat in it. It bypasses the cooler and recirculates the fluid back into transmission until it hits a defined temp. Much faster transmission fluid warm ups and sustained higher temperatures.

Improved Racing 8L90 Adapter

Also, Lokar makes a dipstick that fits the 8L90 too. You have to set full fluid level using the OEM procedure, then just scribe a line on the dipstick for the "full" mark.

I have the light duty 8L45 without a thermostat in it and an OEM external cooler. At 70F ambient it takes 45 minutes to stabilize to 135F. I've never seen it above 145F in 95F weather and stop and go traffic. If it is below freezing my transmission will barely crack 90 degrees. I plan to install the thermostatic adapter above just to maintain consistent temps through the seasons.

Well, since I'll be using the cooler in the radiator as well as the auxiliary Derale cooler, bascially the engine temperature will warm it up and the auxiliary cooler will bring the temperature back down with the fan coming on at 180 and turning off at 165, so I'm hoping to keep it under 200 with this combo, but still be able to warm it up fairly fast

 

[Stonecoldtx]

As long as what you have iis the blue label version of Mobil Synthetic ATF LV HP, if what you have is the black label version then do not use that.

The two cases I have are the Blue label variety

 

[AdmiralYoda]

My application is a 2021 truck, different apples, but I have the OEM cooler in the radiator and the OEM external cooler as well. Both are likely not as robust as what you will have in your car. My engine operating temp is 210F also, most likely higher than yours. As I've said I've never seen above 145F and that was in some spirited driving and/or stop and go in 95F weather.

I suspect your fan will never turn on unless you are running at the dragstrip with little to no cool down between runs. Long story short, you'll be fine!