System Design - some insight needed

For discussing the modifications needed for diesel vehicles to run with 2 tank veggie oil conversions.

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System Design - some insight needed

Postby FerndaleFryer » Sat Nov 01, 2008 4:41 pm

First off the stats: 1993 f-350 crew cab, 2 stock tanks, 7.3 non turbo IDI. I ran on blend over the summer, work flawless, I live in Detroit area so I wanted to go with heated system for winter and to get running on pure veg. Started the conversion last month and have put coolant HE in front tank, installed a pollack 3-way valve, still have stock filter, fuel lines run in a bundle with the coolant from tanks, replace the stock mechanical pump (because it broke) with 2 electric from murrays.

Some lessons learned so far:

1. avoid making holes in your fuel tank on the sides, mostly because there are no flat surfaces to get good welds, I put a drain on the bottom of the tank and had no problems with leaks.

Solution: cut a hole in the top of the tank to put in HE, down side is I only put in 1/5 the amount of pipe in the tank to heat it.

Questions:

1. Tank/Fuel pump design:

a. why do tanks have the fuel supply comming from the top? why not put a 90 fitting on the bottom and let gravity fill the line so there is less stress on the LP?

b. I have heard you are not suppose to over heat the tank, so to much heat is bad, but what are the principles here? like if you have a 20 gallon tank and it takes you a week to empty it, then you would be heating that quantity of oil to much? If you get rid of that same 20 gallons in 2 days how can it be possible to overheat? assuming max temp the tank will reach is 200F.

c. I have also read that the heat in the tank is really only suppose to be sufficient enough to relieve stress on the LP, so in colder weather get the tank temp up to around 70F?

d. Electric Fuel pumps. What are you guys using? It seams that all the aftermarket stuff technically is not designed for diesel, here is one I was eying, I know a lot of people recommend the Mallory but that is just a little over the top, I was looking for something around $100. http://www.jegs.com/i/JEGS/555/15914/10002/-1

One last question:

with temperature sensing units, most come with a max of 8 foot lines, this does not reach the front of my front tank, can I cut it and put a 16 gauge solid copper wire and solder it to extend it so it will reach my rear tank? Or is there a electric one that you can put the sensor in the tank and run some wire to the gauge in the cab?

Thx, love the forum
Ryan
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Postby 240Volvo » Sat Nov 01, 2008 7:53 pm

Heating the fuel in the tank accelerates the formation of polymerization. Polymerized fuel will clog your system. You will have to stop and change filters, or suffer other inconvenience and expense. You only need to warm the fuel at the fuel pick-up to get it to flow in cold weather, so there is no point in heating the entire tank, versus the serious threat of trouble to be gained by heating the oil in the tank.

The tank will always have air in it, so if you combine heat, oxygen and metal, polymerization will take place. That polymerized fuel will eventual break up and flow through the fuel system until it gets stuck somewhere. That somewhere will in time choke off the fuel flow. That will leave you unable to use the system that you installed, and with a big mess to fix.

You need a heated fuel pick up, heated fuel lines, FPHE, and a heated fuel filter (preferably both electric and coolant based). After that, perhaps injector line heaters. Look in the classified area to see these products. I like bmwfan's for price and features, but there are others available.
1984 Volvo 240 diesel with a single tank Elsbett conversion: electric fuel filter heater, FPHE, glow plugs, and injectors. Also injector line heaters and block heater, running 20%kero/80%WVO winter blend.
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Postby FerndaleFryer » Sat Nov 01, 2008 8:42 pm

Thanks for the clarification on tank heating design, these were the aspects I assumed to be true but could not find difinitive answers.

The other heating elements you described I am already incorporating into my design, just implementing them as I have the money and as the temperature drops, we have had a couple 30F nights so far and has forced me to up my schedule in the implementation of heating devices.

In the meantime I am still using a blend in combination with the heating elements I have in place.

Another quick question, why is it bad to heat diesel? at what temp is it bad? I assume it is fine up to 100-150F? is there something that happens to diesel under coolant heat devices?
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Postby 240Volvo » Sat Nov 01, 2008 8:55 pm

There has been a lot of discussion of this. Ultra Low Sulfur Diesel (UDSL) looses lubricity at higher temperatures. Some manufacturers of IPs say that it is OK to heat diesel to coolant temps, and others have observed that the high pressure in the IP alone raises to temp of fuel.

I have a single tank system, and I heat my fuel weather I run diesel or VO. You can add 2-5% VO or biodiesel, or another lubricity additive to your diesel tank if you want to be safe.

Thermal shock (switching from cold diesel to hot VO) has been blamed for IP failure in some trucks, so it seems like running your diesel through the fphe would be OK, even beneficial, but this is not my area of experience, only what I have read here and on infopop.
1984 Volvo 240 diesel with a single tank Elsbett conversion: electric fuel filter heater, FPHE, glow plugs, and injectors. Also injector line heaters and block heater, running 20%kero/80%WVO winter blend.
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Postby FerndaleFryer » Sat Nov 01, 2008 9:19 pm

That is also what I have read, people running there diesel and VO through the FPHE right before injection, I know the one reason some people don't like this is the additional time it takes to purge, unless you added another 3-way just for purging cycle.

Back the the tank HE. I guess I have never worked with jelled VO and how it acts with different style HE and then the flow dynamics into the pickup line.

This is a little hard to explain, but the way I am thinking about it is a hot rod put in snow, will it only melt the snow immediately around it or will the VO "fall" into the void created by heat, thereby creating a continous feed of hot VO to the pickup or will the hot rod create a void in the gelled VO and eventually starve the pickup.

I guess I need to freeze some VO and play with heat
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Postby John Galt » Sat Nov 01, 2008 10:53 pm

Nearly all the problems with using VO fuel happen when one tries to use 100% VO in a cold climate, i.e. below 70°F.

Don't be greedy, dilute the VO with diesel and nearly all the problems disappear.

Keep it under ~50% and single tank systems will be adequate with simple non-computerized engines. If the ambient temperature is below 70°F then add heat. With modern engines heat is recommended with any VO fuel.

Want more than ~50% then use a two tank heated system and purge with ~10% VO mix, but keep the VO less than ~80%

Don't be fixated on using 100% VO and it becomes simpler and more reliable
Last edited by John Galt on Sun Nov 02, 2008 11:25 am, edited 2 times in total.
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Postby green bus » Sat Nov 01, 2008 11:51 pm

I'm still figuring my way through a conversion, but I did a lot of reading about 7.3 IDI and issues with the Stanadyne DB2 IP. It helps to read a bunch of opinions about the DB2...many solutions have worked to keep them from failing on VO. They don't like cold fuel, water or starvation.

Here are some links to research (just a sample):

IP Failure 84 GMC 6.2L Suburban

2 seized IPs within 2 weeks

New IP dead on F250

Two injection pumps in 50 miles... whats happening here?

How to convert a '91 7.3

Stanqdyne DB2 Injection pump replacement Ford IDI ( siezed head . sheared shaft) ? ?

And as far as heating diesel, I am following advice of folks who advocate pre-heating the IP with HOT diesel in order to avoid VO entering a 'cool' IP and increasing viscosity...too thick, no lube, snapped shaft... :( Seems like the VO can be at coolant temp before the IP gets hot...but running hot fuel through it before introducing VO solves the probs many have experienced.

I gathered some info about heating diesel at
Heating Diesel Fuel -- merits and risks

Oh yeah, about the lift pump...I am using a Walbro FRB-13, runs between 5-7PSI. The FRB-5 runs at 11 PSI. Still not sure which is best, but I think the DB2 won't handle much higher than 11PSI very well. I bought mine at
Vegpower

have fun!
'89 7.3L IDI in a Blue Bird short bus

VO system: 25gal plastic tank > heated pickup > Webb 525 coolant-heated 30 u pre-filter > aluminum TIH > manual valves > Walbro FRB-13 > 2u coolant-heated filter > 30 pl FPHE > IP
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Postby FerndaleFryer » Sun Nov 02, 2008 7:52 am

John: First off I use your settling system and have read a lot of your stuff on the other forum.

One of the reasons I started to venture away from blending is the hard starts in the morning as the temperature started falling, I experimented with up to 40% kero, 25% D1 and the rest VO and was still having issues starting, which made me start adding heat and putting in a 2 tank system in order to start on straight D1 since it appeared that startups was most likely the reason for coking and premature engine wear.

Plus other people are having success with 100% VO IF they have a proper system so I want to get to that point as well.

I understand your position though.

Green Bus: So is your conversion 100% or are in the process of installing it? I was wondering what your temp was right before the IP with your system with all that stuff.
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Postby John Galt » Sun Nov 02, 2008 12:45 pm

it appeared that startups was most likely the reason for coking and premature engine wear

... especially cold engine starts. That's why I keep the VO mix low, add naphtha to the mix, and preheat the engine before starting when it's cold enough for me to wear a jacket.
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Postby FerndaleFryer » Sun Nov 02, 2008 1:33 pm

Ya thats what I meant about starts, the cold starts, for 3-4 months here the temp is below 32F and for 1 month it will get below 10F, that is one of the main reasons I decided to add heat.
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Start up on cold engine

Postby dragonfly » Sat Nov 15, 2008 5:27 pm

If you start up on a cold engine will eventually kill your compression - thus it will not start up. What causes the problem is that when the engine is cold, the pistons, rings and cylinder wall have not EXPANDED to its fullest. The rings are not tight against the walls thus the VO gets behind the rings and when the engine finally gets up to temp, it will be cooked into carbon. Accumulate enough carbon on each start up and eventually the rings will be frozen in place, thus not holding compression. Eventually each cylinder will drop in compression until there isn't enough compression to start the engine. I speak from a costly ($500 plus for parts and long (3 wks to do the re-ring) mistake. I now start up on D2, wait until the engine is at operating temp, then switch to VO that is atleast 160F before the IP. Switch back to D2 about one minute before shut down. :D
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