The Stovebolt Site Forums The Shop Area Engine Shop Oil on fuel pump

Recently I bought a running driving 1950 Chevy 3100 4-speed with a 235 engine. The engine has 1957 stamped on it so apparently it isn't the original. After I drive the truck I notice there is some motor oil on top of the fuel pump. No leaks from the valve covers, etc. Thought it might be from the road draft tube, so I removed it, burned all the carbon out of it, repainted it, reinstalled it & even put a piece of hose on the end to lower it into the draft under the vehicle. Still get the oil? Noticed that it has the fuel pump with the additional vacuum booster on the bottom and has a cork gasket in it. Could the oil be "blowing" past (thru) the cork & collecting on top of the fuel pump due to the additional vacuum plus the engine pressure? Anyone ever run into this situation that has suggestions to remedy it?

I'd replace the fuel pump to block gasket 1st then monitor.

There's alot of pressure and oil misting going on in the bottom end when running and escaping pressure will find a way to get out.
You did good to clean the draft tube out but it relies on air flowing past the angled slot cut in the end to help make a low pressure area that helps to draw the pressure out. If you want to keep the extension on the draft tube you should cut the end at a similar angle as the original end to replicate the drafting it provides.
It's also SOP to get some oil drips out of a draft tube.
There's all sorts of baffles etc in the draft tube to cut down on the drips but some will always follow the pressurized air out.
Good luck
Dave

What is the source of the 'pressurized air' in the crankcase of your engine, Dave?

I'm just assuming that there is normally some pressure in the crankcase from the high revs of the motor and possibly some blow-by from the cylinders, although the compression in each cylinder is good.

Volfandt, if the fuel pump to block gasket was the problem wouldn't the oil show up on the side of the block instead of a couple inches away on the top of the fuel pump? I realize the road draft tube will drip some oil, but that should be back behind & below the starter so with the normal air flow from running down the highway, isn't this unlikely to blow back toward the front? On top of that, the oil only appears to be on top of the fuel pump & no where else. that is what is driving me crazy trying to figure it our. Might need to strap a video camera inside the engine compartment to try to see where it is coming from.

Blowby and the downward stroke of the piston(s).

Jim, unless theres a serious crack in the block, there's not many places at the front of the engine where the oil can come from.
The fuel pump to block gasket is the easiest choice. The gasket is cheap and theres only a couple bolts to remove to replace it. It's possible the combination pump has an internal leak, doubtful but check your oil for gas smell. Also monitor to make sure the oil level isn't rising. I only mention these as something to check for as I wouldn't put them high on the suspect list, atleast not until you rule out all the easy and obvious causes.
You mentioned the valve cover wasn't leaking but didn't specify if the side cover isn't, that would be my 2nd check.
Good luck
Dave

Assuming it isn't coming from the side cover, check the timing cover. The fan could easily blow oil back.

Really obscure possibility, most fuel pumps have a vent hole in the casting I have seen them leak oil in other vehicles.

Do you still have vacuum wipers hooked up to the fuel pump? If not and the ports from the pump are open then dirt gets in and wipes out the diaphragm. When the diaphragm on the fuel pump goes bad it will pump oil from the crank case onto the ground, the fix is a new fuel pump, replace it with a single stage pump.

I had a new dual action pump on mine a few years back and it leaked oil. Tried another one and it did the same thing. A small leak from the front cover area can also blow back and be caught by the pump body.

The pin for the arm of the fuel pump can leak and cause a mess. Clean both sides where the pin goes thru the pump and put a dab of sealer on each side.

Jim. Been there done that with the oil on the fuel pump. Everything they said is valid, do check all of it. Now here's where I found my oil coming from on my 235.

The oil draft tube has a plate with a fiber filter on the inside of the block. It is held in place with two screws from the outside. mine were leaking and while trying to figure where the oil was coming from I took them out. Mistake. Had to pull oil pan and pick the plate out and rescrew it to the inside of block. I used some permatex to seal the screws and stopped my leak. I hope this helps.Larry

I have electric wipers, but the ports are plugged.

This sound like the most obvious explanation. My assumption has been that the unused vacuum pump has been pulling oil into the bottom of the fuel pump and that plus the engine pressure is forcing it thru the cork gasket & air from the fan is blowing the mist onto the top of the pump. I am going to replace the cork gasket with another type to see if that works. If not, then it will be the pump to block gasket & if I still have the problem, I guess I'll just have to replace the entire assembly with a new fuel pump with no vacuum booster built into it. Thanks for all the suggestions!

My confusion comes from the fact that on my 216 there are multiple vents in the valve cover that do not have any pressurized air being forced out of them. If there was pressure in the crankcase, wouldn't it travel up through oil drain-back holes in the head and blow out all over the engine compartment via the valve cover vents?

After 1955-1st series, there were no vent slits in the valve covers; however, a vented oil filler cap was used. Pressure in the crankcase would be forced out any venting "opportunity".

By design the vents in the 216's valve cover admit fresh air when the engine is running and this air along w/the byproducts of combustion exit out of the engine via the draft tube. It basically drafts from top to bottom. Later model engines reversed the draft to both enter and exit from the top.

When the PCV system was 1st introduced in the Stovebolts the PCV mounted in a modified draft tube and the fresh air intake routed from a hose vent on the valve cover that was routed to the air cleaner so the air was filtered before it entered the engine.
I've also seen vented oil fill caps be the fresh air intake.
The PCV system I have uses the 3 vent valve cover and vented oil fill cap for fresh air intake.
When I 1st got my 216 running the engine had so much blowby that I was getting smoke out of those valve cover vents at all engine rpm. The rings loosening up and sealed better along w/the PCV system I added has almost completely done away w/the smoke and blowby exiting out of those vents.

ICE designers want the inside of the engine to be a lower pressure than the ambient to minimize internal pressures but when the engines wear the blowby increases and gets somewhat compressed in the crankcase via the downward stroke of the pistons. Normally these pressures aren't enough to blow through seals and gaskets but running oil levels higher than recommended and normal wear and tear will start spitting oil out. A blocked draft tube and or no internal drafting can cause it also.

Anyways pressureized air might have been too strong a term to use for the air/gases that get compressed in the engine block, perhaps "slightly" higher than ambient air pressure would have been better.
Dave

For everyone's information, I removed the fuel pump since I couldn't figure out where the oil was coming from and to my surprise there was an open port between the fuel pump & the block. Turns out the previous owner (?) installed an aftermarket fuel pump with the vacuum booster on the bottom then put in electric wipers (go figure). In the process he either forgot to or missed this port altogether (as did I) until I removed the pump. Figured it would be an easy fix by installing a plug. Well, it turns out that the opening is a Metric (M10x1.0) and no one had a plug or an allen screw. Back to good old yankee ingenuity, I bought an M10 x 1.0 hex head bolt, cut it off to the length of the existing plug and used a hand file to square off the cut end so that the same wrench would fit both plugs. Then a little anti-sieze compound, a few turns of the wrench & voila', no more oil on top of the fuel pump. I'm just curious to try to figure out how long this has been like this & running! I'll go thru my receipts to see if I can find out when the fuel pump was purchased, but my guess is that it has been around a decade, since the previous owner told me it has been sitting in his garage for over 7 years with occasional startups and yard drives just to keep things lubes, etc. Thanks to everyone for all the suggestions and tips as to what was causing this issue. No onto the next project!

Well stated Dave.
Carl

I am very happy with the PCV system that just uses a vented oil filler cap on the valve cover and a PCV valve replacing the road draft tube connected to the intake manifolds vacuum port. So far there have been no ill affects as of yet. I feel good about it because I would rather these lower engine gasses be removed right away. I have no mechanics degree and no proof its the best idea, but it works really well for me.

Well, I guess I spoke too soon! With the plug in, the oil stared coming out of a rectangular hole up on the side between the fuel pump & the vacuum pump. It was quite black even though I had just done an oil change. This was even more oil than before. I took the plug back out & now there is only a small amount of oil. I think it is time to scrap the combination fuel/vacuum pump and go get just a new fuel pump. Hopefully this will solve the issue.