Mechanical fuel pump with two fuel filters. One before the pump and one afterwards. The one before the pump has fuel but it is bubbling. The one after the pump is practically dry. Fuel pump is new and just in case of a weak diaphragm I replaced it with another new one. Generally occurs after twenty minutes of run time.
Replaced mechanical pump with electric pump rated for 6 psi and every thing runs great for about 3 weekends. Still running two fuel filters. One before the pump and one after. The filter after the pump is dry and the one prior is full. Not for sure what the problem is, but I still have the mechanical fuel pump on the boat so I reroute the lines back to it, just to try and finish enjoying the weekend. The problem with fuel bubbling in the first filter returns. So I put the electric pump in line with the mechanical but no luck. I pulled the inline filters in the Holley 750 and they are clean as a whistle.
While limping back to the dock (intermitting getting to plane out) motor begins running rough, wonít idle and the oil looks like a milkshake.
Here are the facts:
Gate valve open fully since day one. (didnít know I should adjust it)
Used a turkey pan (didnít know I wasnít suppose too) Eldebrock Torker 455 intake
Water temp gauge broken (so I have no idea what the motor temp was, boat is a project.. arenít they all)
455 engine with Indmar log exhaust manifolds.
All new plumbing hoses with excellent water flow when on trailer using garden hose.
I have since take the motor out and tore it apart, but cannot figure out exactly where the problem occurred.
Fuel tanks have been cut in half cleaned and welded up this summer.
Generally never turned more than 3500 rpm.
Here are the questions:
Do electric fuel pumps get weak diaphragms or do they just quit working?
The turkey pan looks fine, would it be evident if it was the problem? Such as a rip?
What temp does vapor lock occur? The engine never seemed all that hot.
Well, first thing, milkshake oil is not good. Blown head gasket or worse...cracked block or head.
Where are the pickups located in the tank? Does the problem happen with full tanks of gas? My thought is the pickups are too short or clogged. Do your fuel tanks have vents or are they vented through the caps?
Can any one else back me up,but when useing a mech pump only one filter should be in front of the pump and when with a electric the filter should be between the tank and pump only.You need to get a temp that works ,your valve being wide open is way too much pressure.
Have you tried changing the filter before the pump. If it is partially clogged then the pumps might not be able to suck enough fuel. Even an electric pump has a much lower suction pressure than output pressure. If the filters are both good it shouldn't hurt having two filters. The filter before the pump should be a lager micron than the filter after the pump. The theory is the first filter catches the big stuff and the second filter catches the smaller stuff under more pressure. The first one is a particulate filter and not a water filter isn't it? If it's a water filter make sure it is drained occasionally. As for milkshake oil, it is possible when you hooked the boat to the hose you had too much pressure from your house and you blew it by the gaskets. If the motor was pulled and torn down make sure you have good head gaskets and put it back together.
Wow, lots going on here. In addition to the advice you will read here in response to your question, I would definitely research the olds(may not be enough info on this site due to its recent conception, but the hotboat.com site will surely have the info you need. (Just dont spend too much time over there, all the good contributors are here now for reasons I will let you research if you are new)
Fuel system: It seems like you are sucking air to me. I would have thought maybe some debree in the tanks possibly also, but sounds like you took care of that. Are the tanks vented? What kind of filters are you running? DO they show any signs of collapsing? How about the tanks?(Pre cutting in half...)? Id lose one of the filters.
Olds Motors: Believe half the stuff you read about those things. More specifically, believe the part about all the problems they can have(oil system mostly) but believe also that those probs can be fixed. Dont believe people when they say that motor cant be made to run in a jet boat, simply not true, but you will want to adress the issues if you want any longevity out of her.
Turkey Tray Throw it out. Pain in the keister. There is a Chevy style(fiber/paper gasket). I like to use weatherstripping adhesive around the water ports on the intake manifold, but RTV will work as long as you take the time to set up the water system on your boat. Learn how to do it right the first time and it will never fail on you.
Water System: Take the time to study water system setup & decide which of the several setups will work best for you. Setup will depend on amoung other things, exhaust system(headers or logs?,cooling needs(hi performance motor will use a different settup than a stock one)
Very few homes will have enough water pressure to blow the gaskets when running on the trailer from what I have read/experienced.
Put the motor back together, address some of the problem areas(restrictors, drains, oil capacity, RPM's.) Sounds like you are off to a good start if the motor shows no signs of trouble. Set everything up right and it works, but you as the boat owner needs to understand these systems and others.
If you decide you want a hard running boat that you can put your foot in and leave it there, lose the olds. If its a ski machine that will never see sustained high rpms, go olds.
Last edited by Brendellajet; 07-06-2008 at 09:41 PM.
For the fuel problem I seriously doubt if it's fuel pump related as both pumps have similar problems. I would look closely at the vents in the tanks first and then I would look at the pickup tube(s).
Start the gate valve at the pump around 1/3 open, adjust it by a working temp gauge and adjust the gate valve to get the temp where you want your engine at. There are 1,000 different opinions on what the "correct" temp. eBay there is usually many very cheap temp gauges that would work better than no temp gauge.
Never use a valley pan (turkey pan?) with a aftermarket intake on a Olds. I have seen many Olds get water in the oil just because of a valley pan with a aftermarket intake manifold. FelPro makes a specific gasket set for use with the Olds and a aftermarket intake. If I could see the parts in front of me and they looked like you say they look (good), I'd bet my money on the valley pan being the sole culprit on the water in the oil issue.
Vapor lock is when the fuel in a fuel line gets hot, not when the engine gets hot. If you're concerned about vapor lock still, just make sure the fuel lines are further from the engine than they are on a car and you'll be fine. Under the hood of a car is a lot hotter than in a jet boat.