P30 Oil Cooler Leak

BigRabbitMan wrote:

turbojimmy wrote:

None of the '84s had an in-tank pump installed by GM. They were all mechanical. In 1984 GM conducted a study in conjunction with the motorhome manufacturers to get to the bottom of vapor lock issues. Their suggestion, among other things, was an externally-mounted, aftermarket fuel pump to slightly pressurize the feed line to the mechanical pump. In 1985 1/2 this arrangement became standard using GM parts. Not sure at which point they switched to an in-tank pump, but I suspect it would be the same year they went to TBI.

GM never would have installed a fuel pump without a pressure switch - it's a safety hazard. I'm sure, however, lots of people installed external pusher pumps without an oil pressure switch. Whoever installed my pump did it right - with a pressure switch (now leaking) and the recommended 1/2" steel line running outside the frame rail from the rear to the mechanical fuel pump.

The pressure switch isn't your regular on/off idiot-light switch. It has 3 connections on it that provide 12V to the fuel pump. One connection is hot only while cranking - this gets the pump going without oil pressure. Another connection is fed by the accessory circuit (key on hot). This will provide power to the fuel pump once pressure builds and you're no longer cranking. The third obviously runs to the fuel pump.

Someone had run a constant hot to the accessory side of mine for some reason. If the switch is functioning properly it wouldn't matter, but if it failed the pump could theoretically run constantly. I plan to tap into the correct circuit if/when I install the pump. I haven't had any vapor lock issues (knock on wood) despite having the water temp get pretty hot on hot days.

Good discussion of how the system works and how it should be set up.

Thanks. I know it's a digression from the original topic but for the benefit of those that stumble upon this thread looking for advice in installing an external fuel pump in conjunction with the stock mechanical pump, here is some more info from Airtex from whom I bought the pump and switch.

Their advice is to install a switch in the dash in addition to the oil pressure safety switch. They say to only run the pump when you are experiencing vapor lock issues or think you might. The rationale is that if the stock mechanical pump fails in a manner where the diaphragm is compromised, the external pump will fill the crankcase with fuel and destroy the engine in short order. Not a likely scenario, but a possibility nonetheless. They said that the mechanical fuel pump will suck through the non-running Airtex pump without a problem. BUT, the Vapor Lock appendix in the GM Motorhome Service Guide says that sucking fuel through a non-working external pump could exacerbate vapor lock issues. I dunno who to believe.

I think I'll roll the dice and install the pump the way GM recommends - without a separate dash switch. Eventually I may do away with the mechanical pump completely.