VW oil cooler as WVO heat exchanger

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tawney
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VW oil cooler as WVO heat exchanger

Post by tawney »

Basically, my design isn't working, and I can't figure it out. I took an oil cooler from a turbo engine and used it to heat the WVO. Here's what I did: I took a flat piece of 1/4" steel drilled it and tapped it to bolt a VW filter flange to it. Then I drilled and tapped the back of the steel for two 3/8" brass fittings with 1/4" barbed hose connections where the 'in' and 'out' on the filter flange are. Mounted the filter flange to the steel with gasket and gasket sealer, installed a new oil cooler O ring; installed the oil cooler, and installed a new oil filter. Connected the fuel line going to the IP on the brass fitting that would pull fuel out of the center of the fuel filter, and connected the line from the fuel tank to the brass fitting that would allow fuel to flow into the outer chamber of the filter. Connected the water/coolant lines to the oil cooler.

It heats the fuel quite well; problem is air in the fuel line. I've changed to a different oil cooler, swapped to different oil filter flange, used clamps on the hoses, changed filters, swapped O ring, removed and re-installed the brass hose fittings. Nothing has stopped the air from entering the fuel line: clear fuel goes in the system, bubbles come out. The only time bubbles don't come out is when it is cold; after warm-up there are lots of bubbles. Vacuum is around 4.

I'm more or less convinced that it is the design of the gasket on the filter, or the O ring between the cooler and the filter flange. I can't really see how they could hold 100 psi or more under pressure, but won't hold against a little bit of vacuum, and I don't see much difference between the gasket on the fuel filter and the gasket on the oil filter.

Any ideas about what the problem is, or how I could fix it?

Thanks,
Steve
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Post by Fatmobile »

4"vacuum at idle? :shock:
I suspect a fuel line restriction.
The vacuum is probably pulling air out of the fuel and expanding it, the fuel can't expand so the air has to do it all.
Might not be air leaking into the system.
Take a syringe and draw in a liquid. If you pull the syringe back quickly there will be a large amount of air in it until it fills with liquid,.. then there is no air,...
where did it go?
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libbybapa
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Post by libbybapa »

Why not just use a fuel filter housing?

Andrew
tawney
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Post by tawney »

Thanks for the response, Andrew.

To use the fuel filter housing, I would have to have the threaded pipe nipple long enough to go through the oil cooler; even if I could find that, the diameter on the seal of the fuel filter is smaller, and I'm not sure it's compatible with the oil cooler. I'll check on that tomorrow.

Air is getting in the fuel line because I see it exiting the pump through the return line. It is indeed possible for spaces to show up between sections of fuel, as in the syringe analogy, where there is virtually no air in the space, but the amount of vacuum has to approach atmospheric pressure, roughly 30" or 14.5 psi. If that were the case, though, there wouldn't be a more or less equal amount of air leaving the pump. In one unfortunate incident recently, when I loaned my caddy to my daughter and son in law, the amount of air was sufficient to put them on the side of the road 400 miles from home. (It may take me a while to live that one down!)

But, I guess for my purposes, the more important issue is that you think the gaskets on the cooler and the filter probably shouldn't leak at low amounts of vacuum? I am getting 4" of vacuum according to the gauge; not sure how accurate it is, (it's the $10 model,) but if I'm running 100% diesel with a new filter it reads right next to 0.

One of the vexing problems is the difficulty in pinpointing the source of a vacuum leak; pressure leaks seem so much easier to find. I've tried applying dye at suspected leak locations without results.

I'm at the point of either installing a low pressure electric pump between the tank and the heater/filter, or abandoning the whole idea of using the oil cooler as a WVO heater. It just bugs me that I can't find and fix the problem!

Steve
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Post by Ziptar »

You can use the VW Sandwich Cooler on the VW filter housing, they work great. As for the nipple to thread it together.

the original site is gone but if you google for Eckes WT you'll find some info about it, mostly German.

Another way to go is to use the sandwich cooler from a Volvo 740 on the VW filter head.
Info here.
http://forums.vwvortex.com/zerothread?i ... d=51594434
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Post by tawney »

I think I've found the problem, and now it seems so obvious: I was adding about 10% gasoline to the WVO, and when it's heated, especially under a bit of vacuum, the gasoline vaporizes. Hours and hours chasing the wrong problem when the solution was so simple! Good part is that now I have four different fuel/coolant heat exchangers, and I think they're probably all airtight!

Thanks for the help,

Steve
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Post by Fatmobile »

Glad to hear you figured out the problem.
Yeah a small vacuum with heated gas would probably create vapor bubbles.
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Post by tawney »

Just a quick update: I eliminated the gasoline; no more gazillion tiny bubbles, but the intermittent big ones just kept on coming. I simply could not eliminate the vacuum leak at 4" of vacuum when hot. So, I caved in and installed an electric pump between the tank and the filter/heater combination. It totally fixed the bubble problem. Two things I'll be looking at next: what is the impact on internal pump pressure, and how well does the electric pump perform when I increase the percentage of WVO and the temperature goes back down; it's been almost 70 F here lately. I may post another update after I've had a chance to check on those issues.

If I had it to do over, I simply wouldn't use the oil cooler as a fuel heater; I think there's something about the combination of the two rubber gaskets, (one on the filter, and one above the cooler,) which causes it to fail under vacuum; they certainly do compress under the vacuum and heat. Still not really sure; just don't know what else it could be.

Steve
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Post by Fatmobile »

I'm not sure how much the electric pump would effect the injection pump.
I think low pressures don't effect it much.
I've heard the Cummins 6BT needs a little pressure at the front of the pump and many have been fit with a pressure switch to warn when the pressure drops below 6psi.
They use what looks like a VE pump, just like ours externally except 6 ports.
I think if you can keep it around 5psi you should be good.
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Post by caveman »

I made and sold about 5 WVO filters using the VW cooler like you did. I went to a machine shop and had them machine a new fitting that has the threads to screw into an after market oil filter mount, then a 27mm nut to hold the cooler to the housing and then the smaller threaded fitting to mount a VW fuel filter. Works fine except i've had some issues to get 5/8 hose to seal tight on the metric bungs of the cooler. Nothing worse than slight sweating. I may have one or two left if you want to use a fuel filter rather than an oil filter- which won't have a water seperator or water block.
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Post by tawney »

Thanks for the information, Caveman; I wonder if you had a vacuum gauge on the fuel line before, (edit: I really meant after,) the filter/heater to monitor vacuum? In my case when it was cold, no air in the line even if vacuum went up to 10 inches; but heated there were lots of big bubbles. I did modify a VW fuel filter mount to accept the cooler, and I'm still using that, which in conjunction with the electric fuel pump works great. I also ran a new heated fuel line from the tank in order to lower the viscosity of the WVO/diesel mix, and hence reduce the vacuum required to suck it through there. So it's actually working really well at this point; I just spent many more hours, more money, and arrived at a more complex solution to what I thought should have been a relatively simple matter, and I still don't know definitively where the air was getting in. But, I've moved on to 'bigger and better' things now: right in the middle of installing a 1.6 TD in an '86 Cabriolet, and it's sucking all my extra time and money, so the Caddy fuel problem is already in the distant past.
Last edited by tawney on Sun Feb 15, 2009 3:25 pm, edited 1 time in total.
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Post by caveman »

To tell you the truth, i never bothered using vacuum gauges for 95 % of the conversions i did. The 3 that i did do, 2 were because the vehicle was using a vowmax fuel filter which has a vacuum gauge on it to tell you when the filter was blocking. I ended up moving the gauge inside the cab for the customer's to see what was going on while driving. On both those trucks [one eurovan,one grumann ] i ended taking the gauge off and putting it back of the filter housing because the vacuum fittings gave nothing put trouble[ and yes i used the right ones, redid them over and over etc.]. In the end all i care about is how well the vehicle operated once initial teething was done. My only diagnostic tool i ever used was the clear line just before the pump, after the valve[s]. Looking at that will tell you everything. I also never used a lift or extra pump on a regular VW diesel, only on PD's. If all the fittings are tight and well suited to whatever unit it was attached to, it will work perfectly. On 90% of the ones i did had a hotfox tank heater, heated fuel filter, heated VO lines [the triple bypass hose from Golden Fuel systems, not the stupid hose in hose that others use] and a Vegetherm 12v inline heater from Plantdrive. Up to now i've done 30 conversions and other than filter changes [after the first time customers have problems] all my systems are still running.
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Post by VW cat »

I wanted to show what someone had done to make a heated WVO filter easily, from a VW engine oil cooler. Check out the last post on page 16. My filter adaptor is shown on the same page just above it including pictures.
http://biodiesel.infopop.cc/eve/forums/ ... 42961/p/16

Our pair of VW auto transmission oil coolers, looped together, are still working well to heat WVO. Phil
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