HJ75 Dual Fuel Tanks - Mysterious Behaviour

[Ashchaya]

I've got a 1985 HJ75 trayback ute that has dual fuel tanks. That much I can say with certainty.

When I first bought this vehicle, thanks to dodgy fuel gauges, I had the opportunity to run both tanks down to completely "empty" on two separate occasions. On refilling, I got 83 litres into the rear tank, and 53 into the main tank. (exact same low-flow fuel bowser used on both occasions)

After reading around the internet I see that this vehicle should have dual 90L tanks. So that's roughly okay for the 83L fillup, but the 53L?

Now I know there is something wrong with the breather that I am yet to investigate, because when I do open the main tank there is a HUGE whooshing sound as air gets sucked in. Initially I thought this was the culprit - after using so much fuel, the vacuum became too great and no more fuel could be sucked out. Makes sense.

So this time when I was running on the main tank, I stopped every 100km to open the tank and alleviate the vacuum. Once again I "ran out of fuel" way too early, so bad that this time I could only get 44 litres into it when I went to fill up again. And believe me, I tried. The bowser first cut out at 34 litres.

This leads me to reckon that the vacuum issue can't be the sole culprit.

Any other ideas? Is there something electrical that could be making it cut out? There is a button on the dash you push to switch between tanks, so there shouldn't be any kind of "automatic" technology under there.

I would dearly love to enjoy the benefits of 2 x 90L.

[SCANAS]

I didn't think dual 90's came about till 1hz power came along. Do they look similar. I thought the tanks back then where 80 and 45.

[CRUZAAMAD]

85 model were still a single tank.
2h slugger, 1hz came out later.

someones has fitted another tank.
the main 90ltrs werent out for years later, at least till the 79 series came out, either 1hz but definatly the 1hd fte range standard. both tanks.

breather problem myself.

[supazuk]

My 96 hzj 75 ute has 2 x 80 ltr tanks or at least that is how much goes into them when empty

[Ashchaya]

Well so much for my internet skills. I got heaps of hits for HJ75 with 2H having a 90 litre tank as standard, and an optional 90 litre auxiliary.

80 and 45 sounds a lot more likely given my filling efforts.

Still, if I wanna get freaky, Brown Davis can replace either or both tanks with a 170L. 340L is a bit silly, but I might go 170L rear and keep the "shot glass" 45 up front.

Thanks for clearing that up guys. Much appreciated.

[dogbreath_48]

I can get 80l into my 87 hj75 main tank.
Is it possible the pickup is damaged? Or it could possibly drawing air in somewhere in the main tank system.

[Shadow]

replace all your rubber fuel lines, could be a hole/crack that only sucks air in when the tank gets low (as the pump is pulling harder when tank is low)

also check the fuel/water seperator, these rust up and also allow air in when the tank is low.

lastly try driving with no fuel cap on, its a diesel so you wont have a problem with fire like a petrol might.

My 60 series was dieing at random times and i finally found the same as you, vaccum in the tank. Had to clean all the breather lines(there was about 4 of them from memory, no idea why so many!!) and then it was all good.

[SCANAS]

I would find out exactly what you have first. ie 2x 90 or one smaller sub tank? I wouldn't get an aftermarket tank when genuine tanks are so cheap at the wreckers.

[BeNoS]

its not the return solenoid not throwing the return to the other tank and refilling the other tank with overflow as your using it. hence your only putting such a small amount in one compared to the other???

[crazy eyez]

i have seen the breather block up on the 75s and then they suck the tank in to around the 55ltrs before then bend the pickup so they only use 45 ltrs so just drop the tank and check the pick up and while its out check all the breather lines aswell..its worth a try .i had to do it to mine ..

[76 Tourer]

I agree with crazy eyes my old 75 series did the same thing. Mud covering the whole top of the rear tank covers the 2 black plastic boxes and the maze of breather hoses and the tank sucks in.

Get a 79 series rear they only got 1 breather hose do a loop of fuel hose to a Z14 filter and zip tie up under the tray or higher