fuel leak - ideas?

[BEACHTRVLR]

Hi all - I am a big fan of the site, haven't posted much, but now have a question for the group...

I have a 1990 f250 4x4 with 7.3 idi non turbo (the one in my sig). Up until a month ago, it didn't leak a drop of fluid anywhere (unheard of, but i wasn't complaining). Now it has developed a very active fuel leak. I thought it was PS fluid, because it seemed to drip off the PS cooler return line, but now I realize it is fuel. If I lie under the truck with it running, i can see fuel dripping at a rate of a drop every 3-4 seconds. It is coming off a metal line that runs up next to the oil pan. I can't see any leak from the top of the engine, and from below, I can't see any obvious source - but whereever it is, it is dripping pretty well. Diesel smell in the cab now, etc. Engine runs great, no issues there. Fuel filter not leaking, fuel/water seperator not leaking. Everything topside looks perfect. Underneath, there is a constant drip when engine is running. When I shut down, the leak persists for a couple minutes, leaving a paper plate sized spot on the pavement. Underside of truck from under radiator back to bell housing gets drenched.

Any ideas on what is leaking, and what to do about it? I am in Asheville, NC, and don't have a regular mechanic (and haven't found a local diesel mech I truest). Any insight is greatly appreciated - you guys are the experts - I am just learning the ropes! Any danger in driving it while is leaks (besides crap fuel mileage, of course).

Thanks!

 

[suv7734]

Sounds like you might want to check the transfer pump. It is located on the passenger side front of the block below the thermostat housing (and behind the vacuum pump if you have v-belts). If you look from below it looks very similar to a gasser fuel pump. There is one rubber line (from the fuel tank switch) and one hard line (to the fuel/water separator) It may be just the rubber line has deteriorated or the pump may be leaking. Not to alarm you but check your engine oil level (make sure it is not above full) and smell the dipstick for a diesel smell since once in a while if the pump diaphram leaks it can cause fuel to enter the crankcase.

 

[argve]

I'm with Bruce on this one. I would suspect that the rubber piece that goes between the hard line that runs along the frame to the lift pump has a spot rubbed through it.

 

[BEACHTRVLR]

Thanks for the quick and helpful responses, guys!
I checked the oil level, and it is normal, no smell of diesel (whew!). I will climb under it tonight to see if I can get a good look at the transfer pump and hoses. Is it easier to see the hoses from topside or bottom?
If neither hose is leaking, but the pump itself is throwing fuel, how hard is it to change, and can you get one at the local parts store?
And one last dumb question - should I be worried about driving it in this condition due to fire hazard?

 

[Mr_Roboto]

There is little fire hazard, I've driven diesels with fuel leaks for months on end.

You may want to pressure wash the engine (engine stone cold) to get the grease off and help you locate the actual source of the leak.

 

[suv7734]

I checked the oil level, and it is normal, no smell of diesel (whew!).

Good News

I will climb under it tonight to see if I can get a good look at the transfer pump and hoses. Is it easier to see the hoses from topside or bottom?

Easier to see from the bottom

If neither hose is leaking, but the pump itself is throwing fuel, how hard is it to change, and can you get one at the local parts store?

It is a bit time consuming since it is somewhat buried so you need to be patient. Local parts store will have/be able to get one. Some here also suggest using a small electric pump (Holley 'red' or equiv) in place of the mechanical and just using a BB Cheby block off plate to seal the block; your call. If replacement is required and you go with the mechanical be sure to read the directions with regard to the position of the cam lobe before installation. If you decide to go with an electric post back for location and install tips.

And one last dumb question - should I be worried about driving it in this condition due to fire hazard?

No such thing as a dumb question- the small leak should not create a hazard, just makes a bit of a mess.

Bruce

 

[hesutton]

Also have a look and the metal lines running under the engine and up the fuel filter. I had a nasty leak when I first started the truck during it's project stages. The metal line running up from where the mechanical pump used to be (I have a Holly Red and mechanical pump delete) had rubbed on the filter bracket and made a hole. Luckily, I had a spare line. These leaks can be a PITA to locate, but I'm sure you'll find it soon.

Heath

 

[BEACHTRVLR]

Update - I haven't had time to climb under the truck and check the pump yet, but after driving it to work today, some new developments...

I was running on my rear tank (1/4 full), and when driving at highway speed, switched to front tank (full). No problem, business as usual. But then I stopped to drop off my '59 Land Rover tailgate at the local shop for reconstruction (a whole different project, off topic!). I noticed a fair amount of steam/smoke coming from under the hood. I pop it and check, and it is coming from the leak dropping on the hot exhaust just at the back of the oil pan. I notice that the leak is much worse now, dripping constantly, and some is getting thrown up into the engine bay by the fan (belts are staying dry).

I let it cool off, smoke quickly goes away, dripping stops. After 15min of shooting the breeze on LR stuff, I switch the tank back to the rear, and fire it up. Drive 15min to the house, shut it down, look for smoke, leak, etc. No smoke, leak is back to normal drip level.

So my current question is - is there any reason that the leak would get worse/better depending on what tank it is drawing fuel from, or the fuel level in the tank? And does this still point to the pump and associated hoses or something entirely different?

Thanks again for tolerating all the questions! Planning to get under it this week, and will be using your advice to get it sorted out.

 

[Agnem]

If there is a problem with the fuel return, or the FSV, you may be leaking at the returns due to high return line presure. This would be my guess. Try disconnecting the return line at the return manifold in the back of the engine, and blow through it. Switch tanks, and repeat. Make sure you can get the air through. Now that they have leaked, you may have to R&R your lines, caps and O-rings to get it back to not leaking.