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Re: [GMCnet] In tank fuel pumps, or external pumps. [message #316379 is a reply to message #316377] Fri, 21 April 2017 10:21 Go to previous messageGo to previous message
emerystora is currently offline  emerystora   United States
Messages: 4442
Registered: January 2004
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Senior Member
Gasoline does not have to boil to cause vapor lock. It just has to vaporize. Liquids can change to a vapor well below their boiling point. Just look at the roads after a rain. The water dries up from the road by changing to a vapor into the air and yet the surface of the road is not at 212 degrees, the boiling point of water.

I had an external electric pump just outside my tanks but still got vapor lock at times, especially at the high altitudes here in Colorado.

I installed the in-tank pumps in 2010 and have not had any vapor lock since. They now have about 8 years on them and no failures. I probably put more miles on each year than most of you. I have gone to Michigan and to Florida each year plus most of the GMCMI conventions.

My feeling is that if a pump should ever fail on a trip I can get by with one pump or I could easily mount a pump outside the frame rail where it used to be and pull through the failed pump if I am 2000 miles from home and don't want to fill as often.

It will be interesting to see how many years the pumps last.

The in-tank pump in my 1973 Jeep Grand Cherokee never failed in the 20+ years I owned it (over 200,000 miles) so in-tank pumps seem to last a long time. I think people's fears of pump failure are overrated. Of course it can happen but it's a risk I can accept. My pumps are Airtex. I would not buy cheaper pumps.

Emery Stora
77 Kingsley
Frederick, CO

> On Apr 21, 2017, at 8:42 AM, Bob Dunahugh wrote:
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> To get 87 octane gas to boil. You need temps that are approaching 200 degrees. Those are temps that you can't touch. I've had an electric fuel pump near my tanks fail on a day when the temp was near 100. The tank, pump, and frame were no were near that. Maybe 125 at most. That day I was pulling my enclosed trailer. GVW was at about 21,000 lbs. Anyone in the Southwest. Check the temps on days like that. Gas just can't boil back there. Even on a hot day.
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> A hole in the floor is fine if you have carpet. But a vinyl, or other hard surfaces to me is an other subject. In our burned 78 GMC. I had the electric pump just at the front of the tanks. I never had vapor lock. Even being in Arizona during a hot week in July. With my tanks being at 115 degrees. And with the amount of gas coming out of those tanks to cool those gas lines. Apparently gas got to my carb before the gas got to a temp to create a vapor lock condition. So I just don't see how moving the pumps just outside the tanks can help reduce vapor lock to any measureable degree. That 115 degree gas might hit the external pumps at 118 degrees. That's along way from vapor lock temps. I don't see in tank pump as a bad idea. I just would like to find a reason to justify the extra work for me. Bob Dunahugh
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> Both ways have their own good, and bad points. Pulling tanks isn't a real big deal. It's the getting the GMC high enough to do it. And if your on the road. That really gets more complicated. I'm going to put in 1 pump per tank. One way, or the other. And take the tank selector valve out. So since I'm thinking of external pumps mostly for simply of installation, and access for repair. What's the advantages of the in tank installation? Bob Dunahugh 78 Royale
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