engine dies after 2 hour run

[Horus]

After a stop, check if diesel is coming to the injectors. If not your high presseure diesel pump is probably hanging! Do you have very old or bad (bio)diesel in your tank?
The pump might be hanging by a higher engine temperature.
You can try to put 1/4 liter (at about 100 liters diesel) ATF oil in your diesel tank. It will be good for al your engine parts especially the diesel pumps.
If it doesn't help it's only good for the engine, and hou have to have your pressure pump serviced. Succes.

[gulfcoastsailor]

Pinhole air-leak fur shur. Good luck 👍

[JordanH]

I think that most people above are suggesting an air leak.
I once had an auto mechanic help me get my engine working again... we didn't have the right hoses and parts so we cobbled together a solution. When he checked and refitted my mechanical fuel pump, there was a critical crush washer that he reused instead of replaced. The engine ran really well at all RPM's, but under load would die. The re-used crushed washers sealed 'only so well'. Replaced the washers and all was well.


I'm thinking something similar is happening to you, but instead of load, I'm thinking heat is causing something to expand and let in air. I think the "~2 hours" is probably getting to the point where something has had time to heat up and expand.


I'm going to float an alternate possibility. I don't think it's the case with you, but it might be. I had this issue where I had the inside of my fuel tank rust and flake but no inspection hatch so i didn't know. On calm days, it would work really well, but on rough days, my engine would quit after time... Rust flakes were getting sucked up to the fuel intake and blocking flow. Then the engine would quit, the flakes would sink, and I could restart the engine and continue - until another flake would get sucked up. They were too big to go into the intake, so the filters looked clean-ish, but the effect was the same.


Is it possible that you've got rust flakes or algae blobs floating in your tank and clocking the intake?

[abarrow]

Did a passage on a boat with a similar problem. It was ultimately tracked down to a pinhole leak in the fuel line.

[BonesD]

Sounds like a vacuum lock to me as it corrects itself after sitting. If it had an air leak I cant imagine why sitting a few hours would resolve any difficulties. Not like the air leak would repair itself and re-prime the pump. But it might!
I like the idea of loosening the fuel cap and running for several hours. If it doesn’t fail then check the tank vent.
I also like the idea of running off of a five gallon tank and eliminating the tank and plumbing to help narrow the search.
Has this problem started with warmer weather? New fuel line instal or routing?
After a filter change? Do you have a vacuum gauge on the Racor. You say the Racor looks good but did you to change the filter?

[musicengineer]

Try keeping the fuel line to the carburetor cool.
Couldn't wade through all the responses, and don't know if she's gasoline.
But if you want to know why, call me at 610-388-7903 (leave message) and I will explain how my atomic 4 did this, and why. Chic Bach

[Tsuru]

We have a Catalina with the Universal M35B. On our boat and probably most Catalinas the electric fuel lift pump shutsdown on low engine oil pressure.
I changed our oil pressure switch last season for this problem. As part of the repair I went through and inspected the wiring and connectors from the switch to the lift pump. Several looked ok but the pump would start and stop when wiggled. Ended up changing most of the connectors for reliability.
As a side note our boat runs without the lift pump when the tank is near full. Somewhere around 60% the lift pump is required. I don’t know if this is unique to our boat or not.

This is how I’d proceed
#1 Remove insect nest plugging the fuel tank vent thruhull
#2 Clean strainer on the bottom of the Faucet fuel lift pump
#3 Find pin hole leak in fuel lines
#4 Inspect wiring to lift pump

[chasfgr]

Unfortunately there are myriad reasons for the described symptoms.
In rank of likely reasons (all of which I have experienced)



1. Lack of air into the main tank, causing a vacuum, such a blocked air-inlet was a wasps attempt at a nest at the end of the breather pipe.
2. A leaking pump diaphragm ( as long as the fuel level is above the pump level it works). Another clue lies in a very poor fuel consumption, and yet another in a rising oil level as diesel leaks into the sump.
3. A nasty mass of floating water and muck finally getting to the tank down-pipe. (That is easily rectified, pro tem, by increasing the height of the pick-up from the bottom of the tank.

Very seldom is it the pump wearing, though that is possible and always the first (and most profitable) analysis by a "marine mechanic".
Yanmar engines are prey to that last problem - I always carry a spare, after being sucked between Scylla and Charybdis on one excessively Odyssean experience.

[David Mathis]

Diesels will almost always run, other than the rare mechanical failure, if they have sufficient fuel. So, what could be causing the fuel problem? As DNK suggested, place a vacuum gauge tee at the connection closest to the intake side of the injector pump. It is also recommended that you temporarily replace the last section of fuel line before reaching the engine with clear line to determine if air is getting into the system. Most likely, you have one of the two most common problems, loss of pressure or air getting into the system. If you see high vacuum just before it stalls, the problem is a blockage in the fuel line or tank. If you see air in the clear plastic tube, it's an air leak. Disregard the small Champagne bubbles, they're normal. These aren't the only possibilities but they are the most common of the easy to find problems.

[BonesD]

I meant to write vapor lock, not vacuum lock.

[musicengineer]

It was a vapor lock on my atomic 4 and I wasted a lot of time finally realizing that I forget that that happened to my 1949 chevy 6 all the time!

But, you need to understand what a vapor lock is in terms of fuel supply and how it is exacerbated by ethanol which I read as decreasing the vapor evaporating pressure at 140 degrees to 130 degrees. Chic Bach

[Cadence]

I didn't go back and read all suggestions. If this is redundant I apologize. Is it as simple as a plugged or partially plugged tank vent and it takes two hours to create sufficient vacuum in the tank to starve the engine. Mud dobbers love those little holes.

[Wolf Pack 2]

I had a similar experience, it was an air leak that over time would shut the engine down and after a period of time run like normal again. If you have a clear bowl on the bottom of your racor, check it after a period of time for any small air bubbles. If so, simply replace your fuel line.

[Tillikum]

Insert a piece of clear hose or a sight glass into the fuel inlet line as close to the injection pump as possible. If there are air bubbles you will then be able to see them, if you're watching.


Worth checking TFM too.

[musicengineer]

sorry, I checked and its diesel !