-Single Tank VS Dual Tanks-

A comparison of single and dual tank systems.  What has and hasn't worked for me.  Your mileage may vary.
Single Tank Systems
Over the last 12 years, my overall experience with single tank systems and WMO hasn't been ideal.  The issue is that we tend to get a bit greedy and push the limits of what a single tank setup can do without causing issues.

Blend wise, I try to stay at 50% or less when it comes to running a single tank.  That's 50% diesel to 50% oil blend (W80, 85, 90, etc.).  Yes that means you'll be spending more at the pump...  but it also means you'll slow or eliminate a lot of the issues that come with a single tank system.  The main issues that come up with a single tank stem from short drives and starting/shutting down on oil.  Oil blends require quite a bit of heat to burn clean.  Cold starts on heavy oil blends are typically difficult and smokey.  That smoke/haze is unburned fuel which leaves deposits on injector tips, valves, rings, etc.  The heavier the oil blend, the more of an issue this becomes. 

Even at 50%, a few short trips back to back to the local convenient store or what have you where the engine never reaches operating temp or sees a heavy load and you'll likely start seeing a consistent haze from the exhaust.  This is because the injector tips have started to "coke" or carbon up.  Typically speaking, as soon as you get out on the highway again, it'll clean back up and the problem will go away.  This happens MUCH faster as the oil blends go up beyond 50%...   when we start getting greedy.  I could typically go a few weeks on a 50/50 blend without much issue..   but 70% netted heavy hazing at idle even when at operating temperature.  It would then take 2-3 tanks of diesel fuel and hard driving to clear it back up.  If left unchecked, the injector coking will continue to get worse until power starts to drop off...  cylinder misfires start happening...   etc.  At that point, the only fix is to remove the injector(s) and manually clean them either in solvent or with a brass wire brush.

Moral of the story...   stick to 50% or under in single tank systems and don't be afraid to plant that skinny pedal from time to time.  Limit short trips as much as possible, as well as idle time.  When needed, run a tank of straight diesel and put it under a load to knock down hazing and clean up the injectors a bit.

Dual Tank Systems
Dual tank systems are my go-to for running WMO in high blends for long periods.  Most of my rigs are setup this way where the original vehicle tank stays straight diesel (for startup, shutdown, and short trips) and an auxiliary tank for WMO (typically W90 for me). 

This eliminates many of the issues with running alternative fuels in general.  Being able to start and shutdown on diesel eliminates the hard starting issues.  It also eliminates the cold burn issues with most oil blends and allows for higher blends to be used without issue.  This also gives you a "backup" of sorts if something goes wrong on oil...   you still have straight diesel in another tank with it's own filter to get back home on or clean things up on when needed.

Dual tanks sound great don't they?  BUT...    they have their own issues that must be taken care of.  For starters...   fitting a second tank isn't always easy and there isn't always a "bolt-in" option.  Bed mounted tanks, and small tanks in the trunk of a car tend to work well...  but what about SUVs?  Fabrication may be involved in getting a tank fitted.  Don't be afraid to think outside the box on this though.  Marine / boat tanks are an option as well as fuel cells (nope..  not just for race cars).  Don't forget about a way to monitor fuel level in the tank!

After you have the tank fitted, now you have to plumb it.  There are VERY few options when it comes to electronically controlled valves that will hold up to oil long term and they are typically expensive.  This is why I always try to go with mechanical valves.  Simple 3 port ball valves (1 for supply and 1 for return) makes for a very reliable system that is typically inexpensive.  Yes that means you'll need a place to mount the valves which may mean drilling holes in the floor of your vehicle.  You'll need to come to terms with that.

Once you've decided on valves and placement, then you'll need to plumb everything.  I typically use 1/2" ID hose or tubing for this.  Yes it is large but that's for a reason.  Oil blends are thicker than diesel, typically speaking.  The easier the oil can flow from the tank to the lift pump, the better.  I also typically run a remote filter head between the oil tank supply and the valve with a good quality filter/water separator.  I try to get a filter with a LOWER micron rating than the main engine fuel filter.  That way, the likelihood of plugging the main filter from the oil side is very slim (maintains your "backup" straight diesel side for if something goes wrong).

Once your tank is mounted and plumbed, you're ready to go.  The separate 3 port valves help eliminate cross contamination between the oil and diesel systems.  With a single 6 port valve, all of the oil in the fuel system will dump into the diesel tank when the valve is switched.  With a supply and return valve, the supply can be switched a few miles before switching the return which allows the system to be flushed with fresh diesel.

The biggest issue outside of actually installing and plumbing the tank is the cost.  Auxiliary fuel tanks typically aren't cheap and prices on hose/fittings are going up just about monthly it seems.  With that said, the headaches saved as well as the ability to run higher oil blends...   it will pay for itself in the long run.

**Dual Tank Plumbing Parts List - CLICK ME**

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