Adventures in Vapor Lock

[vlad_d]

Hello Rovers!

I’ve been dancing around this problem for a year now - stalling, hard starting when hot, leaving me stuck at intersections in the left turn lane and the Series won’t start back up. I threw all kinds of parts at it: new Webber carburetor, new Pertronix distributor , new mechanical fuel pump. Worked okay for a time, and the symptoms returned! Some research into the problem, and it seems everyone with old cars is having this problem now - Vapor Lock - due to new gas additives like ethanol making the boiling point of gas much lower.

Vapor Lock:
The problem seems to be that ethanol in gas (E85, etc) lowered the boiling point of gas in the last 15 years or so. So, on low pressure (carburrated) systems, the gas sits in the lines until the float bowl empties and asks for more fuel. It literally boils and turns to a gaseous state in the lines or the bowl and your engine is starved.

Fixes:
There are a couple fixes, I guess. Either you shield/cool the lines and or carb. Or, run a recirculating fuel filter and electric fuel pump to constantly move hot gasoline in the line back into the cold fuel tank. Or, the nuclear option, get an after market fuel injection kit.

My progress:
I have my gripes about each method…so I started from the lowest one first. My gripes with each method:
* Electric fuel pumps are loud. Without a ‘dead man’ switch, they just keep pumping gas if there’s voltage…so if you get in a crash, they just keep squiring fuel on your burning bones.
* EFI systems are great. But I got a Series because I wanted a classic, mechanical, simple car. Am I gonna put a computer and extra wiring in now? Ugh!

Heat profile:
First thing first, I bought a temp gun to get temp readings in places. I wanted to see where in the engine bay is hot, so I could route the fuel line away. Here are some spot temperatures after a 20 minute warm up drive on a 65 degree California Fall day:

* At fuel pump- 95-110 degrees
* At head, near water spout, right side- 134 degrees
* Top of head, near radiator line- 119 degrees
* At head, left side- 118 degrees
* At intake manifold, near head - 169.5 degrees
* At exhaust manifold, halfway to carb - 272.5 degrees
* At exhaust manifold, right at head - 360.7 degrees
* At fuel bowl on carb - 87.8 degrees
* At phenolic block on carb- 93.7 degrees

So, with the standard routing of the fuel line from the fuel pump, across the front top of the engine and into the carb…we go from about 95 degrees to a solid 120 most of the run, and we pass into the carb over the intake/exhaust manifolds that go from 360 degrees to 167 in less than 10 inches. And this is with my hood up. Likely it stays hotter with the hood down.

Boiling point of gas:
I tried to find exact data, but it’s hard. Gas is blended with different additives at different times of the year. Also, they list “boiling point” in 3 numbers…where the first number is “5% of the gas is boiling”, the second is like “50% of the gas is boiling” and the last one is 100%. So the range they give is like 90 degrees to 300 degrees. Your numbers may vary. So, by my understanding, SOME boiling(5%?) is happening as low as 90 degrees at atmospheric pressure(inside the fuel bowl). The mechanical fuel pump is rated at around 4-6 PSI, so it might boil sooner(like a tea kettle under pressure boils water faster).

So, I guess no wonder it starts Vapor Locking. I bet the fuel gets to about 120-150 and vaporizes.

First attempt to fix:
As I said, I wanted to try the least radical fixes first. So, I decided to route my fuel lines toward the outside of the engine bay, avoiding resting on the block. I also got some heat shielding sleeves for the fuel lines from DEI(DEI-010403) In addition, I got a small finned heat sink tube type oil cooler and put it in the front grill area, just in front of the radiator and ran the fuel line through it. So, the fuel line is shielded, and runs through 65 degree ambient temp around the outside of the engine bay and gets an additional cooling boost from the finned heat sink getting fresh air up front. As an aside, pipe fittings are a nightmare! There are a half dozen standards and good luck finding exact hardware. In my case, the oil cooler had a -6 AN fitting that needed to be reduced to -4 AN, then turned by a 90 degree bend, before outputting to 1/4” hose Barb. That was like $80 of fancy black anodized aluminum pipe hardware and 30 minutes on the phone with a tech to find all the right combos.


Did it work?
Well. Partially, but no. The Vapor Lock came back. Stalled twice. But, I noticed it cooled off very quickly at each stall. I usually had to wait 5-10 minutes to restart. Now, it was back to non-boiling temps in 30 seconds-1 minute. So, less desperate…I could restart in one light change. Whereas before, I was a scene blocking traffic for 3-4 traffic light cycles.

Next steps:
I may look into heat shielding over the intake manifold to block exhaust manifold heat. Might look goofy, but I just need like 10 degrees difference.

But, ultimately, I think I might have to bite the bullet and do the recirculating lines and electric fuel pump. Does anyone have advice on tapping the fuel tank to take a return line? Is there a Land Rover part that works good? I don’t want to reinvent the car. I know later Defenders (EFI) and such have recirculating fuel systems. Any advise much appreciated!