NLC Posted July 20, 2021 Share Posted July 20, 2021 I have a R 686 dump truck with a300 Mack engine. After sitting for a few days you have to spin it over for a while to get it to start. It’s like it loses its prime on the fuel. Is there a check valve in the line going back to the tank that I could take a look at? Quote Link to comment Share on other sites More sharing options...
Red Horse Posted July 20, 2021 Share Posted July 20, 2021 3 hours ago, NLC said: I have a R 686 dump truck with a300 Mack engine. After sitting for a few days you have to spin it over for a while to get it to start. It’s like it loses its prime on the fuel. Is there a check valve in the line going back to the tank that I could take a look at? No clue i'm not a wrench😎 other than the simple things first. Check all the fuel line fittings to make sure they all are tight. I had unbolted fuel filter bracket to get easier access to steering box and in the process of constantly moving it back and forth to keep it out of my way, I must have loosened fittings. I was looking for fuel leaks but it was a suction line that was getting air! Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted July 20, 2021 Share Posted July 20, 2021 You have a leak in the return side of fuel system Pressurize the tank slightly to show the leak A hose clamp and a piece of old inner tube over the filler will show the leak pretty quickly Wind the air regulator on your shop compressor down as low as it will go, once the fuel system is at 10 or 15 psi have a look all around the fuel lines for the fuel leak Paul 2 Quote Link to comment Share on other sites More sharing options...
D-Day Posted July 20, 2021 Share Posted July 20, 2021 I had a similar problem with a 350 in a superliner always had to crank it a long time after sitting for a couple of days finally found a tiny crack in the fuel filter head where the fitting for the line to the pump screwed in gravity was allowing the fuel to return to the tank and partially emptying the filter 2 Quote Link to comment Share on other sites More sharing options...
mowerman Posted July 21, 2021 Share Posted July 21, 2021 Yes I’m sure it’s just a line or fitting… good luck… bob Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted July 21, 2021 Share Posted July 21, 2021 23 hours ago, D-Day said: I had a similar problem with a 350 in a superliner always had to crank it a long time after sitting for a couple of days finally found a tiny crack in the fuel filter head where the fitting for the line to the pump screwed in gravity was allowing the fuel to return to the tank and partially emptying the filter No matter were the leak is I think putting some pressure in the system is by far the quickest way to find a pesky leak Paul 2 Quote Link to comment Share on other sites More sharing options...
mowerman Posted July 27, 2021 Share Posted July 27, 2021 Yes it doesn’t take much to run the prime out a lot of times and it’s not going to fire without assistance…:: bob Quote Link to comment Share on other sites More sharing options...
Red Horse Posted July 27, 2021 Share Posted July 27, 2021 On 7/21/2021 at 4:34 PM, mrsmackpaul said: No matter were the leak is I think putting some pressure in the system is by far the quickest way to find a pesky leak Paul Paul, Point of interest-in my case I was looking for leaks-nothing. I pulled filter and level was below the pick up. so I would refill filter, crank and it would fire up and run for a minute or two then quit. I finally noticed bright brass threads on filter head on what I thought was the suction line-tightened those and end of problem. So isn't the suction line a negative pressure and it will not show fluid??? Quote Link to comment Share on other sites More sharing options...
Brocky Posted July 27, 2021 Share Posted July 27, 2021 Red Horse, Even though the suction line is normally a vacuum line, if you put 5 PSI of pressure in the tank the suction line "should" leak/seep?? Quote Brocky Link to comment Share on other sites More sharing options...
mrsmackpaul Posted July 27, 2021 Share Posted July 27, 2021 17 minutes ago, Brocky said: Red Horse, Even though the suction line is normally a vacuum line, if you put 5 PSI of pressure in the tank the suction line "should" leak/seep?? This is what I would expect to happen, the only leak it wont show up is the pipe inside the tank that returns the the fuel to the bottom of the tank Paul Quote Link to comment Share on other sites More sharing options...
Red Horse Posted July 29, 2021 Share Posted July 29, 2021 On 7/27/2021 at 4:35 PM, mrsmackpaul said: This is what I would expect to happen, the only leak it wont show up is the pipe inside the tank that returns the the fuel to the bottom of the tank Paul Brocky and Paul- I guess my problem was I did not pressurize tank and for sure once level in filter dropped below the "drop" in the nipple that is on the bottom of the filter head, it would quit running 1 Quote Link to comment Share on other sites More sharing options...
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