So I have been running Opti-Lube XPD since my truck was new. I live in East TN so our winters are not as extreme as some but we do occasionally get some cold spells down in the single digits.
My norm has been to dose at the recommended 0.25oz/gallon rate. Now that it is colder I am switching to the 0.5oz/gallon rate.
It is my understanding to get the full rated benefits and best lubricity, one must dose at the 0.5oz/gallon rate year round which makes this stuff twice as expensive as we are lead to believe with the "Treats 512 gallons" label.
My primary goal in running this additive is to provide the best lubricity I can to the HPFP. Seems to me I need to switch to the double dose rate year round.

So I see some claim that XL is much less expensive than XPD per normal dose but to get rated benefits you have to double the dose which brings it up to close to the cost of XPD.
BUT if you have to double XPD to get rated benefits even doubling XL turns out much less expensive per dose vs XPD.

Now the question: Is it safe and does it make sense to mix XPD and XL, both at the normal dose to get all the benefits of XPD and added lubricity of XL without having to double the dose of either? (Yes the added cost of the XL dose does increase overall cost but not as much as doubling XPD)

 

I’ve been using optilube since my 19 was new. I called the company and asked for advice. Since I’m in CA, our diesel has really good cetane so I don’t need that. I was told to use the XL at the premium dose / higher rate. So that’s what I’ve done. I do travel a lot and they told me it was perfectly fine to mix their formulas so i carry some summer blend / cetane boost just in case. I’ve never used the XPd.

 

For xl and xpd, the temps have no bearing on dose rate. Use what ever the instructions say.

however, fuel begins to wax at 50 degrees.....so....you are better off using winter blend and /or summer blend according to climate conditions.

 

I would agree with you on XL but not for XPD since XPD does have an anti gel agent. XPD's dosage recommendation on the label is temp dependent.
However the public test results show that to get the lubricity benefits posted, the premium dose was used. Those results also seem to indicate that XPD is superior to the winter/summer products in lubricity improvement.

 

ok, I see that now.

 

That must be a typo because that is untrue. Untreated diesel does not begin to cloud until 32F and does not begin to gel until 10-15F.

 

my understanding is waxing starts at 50, crystallization starts at 32.

if you run anti gel, it does something to the wax molucues that prevents them from binding to form crystals.

 

I'm no expert but have read plenty of articles regarding diesel fuel and cold weather. The point when the paraffin wax in the fuel begins to crystalize is called the cloud point.

"Gelling starts to occur at a specific temperature known as the cloud point, coined after the white haze — or “cloud” — that appears as paraffin wax crystalizes. No. 2 diesel fuel has a cloud point of 14 degrees Fahrenheit."

Most articles reference 32F as the cloud point of diesel fuel and 15F as the temp when it turns to a solid.

I did find a white paper that stated diesel could cloud as high as 40 if the fuel was of low quality.

 

I run the Opti-Lube Summer most of the year. During the cold weather I switch to XPD ( DEC-Jan-Feb)

 

I get what the OP is saying, but instead of trying to mix and match (which I've wondered too), I'm biting the bullet and running the XPD at the higher dosage for the cold months. Admittedly for me, I don't put nearly the mileage on my truck in the winter after Thanksgiving compared to good weather months. So, that keeps my XPD usage lower and more tolerable. Come Springtime I'll go back to the XL for the rest of the year, which is Opti-lube's highest lubricity treatment.

 

I contacted Opti-Lube a number of years ago (before they came out with that handy chart) and a few things to note from the conversation are:

1. While Boost! adds quite a bit of cetane it does this by lowering the amount of lubricity additive in the chemical package.

2. The main reason for the high treatment rate of the XPD product is to get the required amount of the anti-gel chemical into the fuel.

3. He mentioned that quite a few of their customers mix the Opti-Lube products to obtain the benefits desired.

With the winter blend fuel and moderate winter temperatures here in Michigan I run Summer+ all year long and keep my half jug of XPD for when the temperatures drop below zero. For those in the southern climates that want the added lubricity of XPD I would recommend running a mix of Summer + and XL. No need to spend the extra money on the anti-gel chemical in XPD.

 

We can get away with summer treatment all year since our winter diesel is rated for -20F.