1UZ Fuel aeration. Is this a problem?

[davewanna]

Hey guys, I have a Hiace with a 1UZ in it. I bought it in there and am going through sorting out it's little problems.
I have had continuous cooling problems at highway speeds as you would probably expect. Worst designed car for airflow, VERY tight fit under the seat so it's very hard to get the heat out. (I also like in Katherine, NT so it's HOT here)

Last couple of days been having more cooling issues than normal and I have noticed I can hear the fuel priming a lot louder than normal before starting. I have pulled the seats out today and have found with the engine off, key to ignition and the fuel pump runs I can feel the return hose from the regulator vibrating with the noise. Repeated priming makes the same noise most of the time, intermittantly it is quiet.

What could cause this? (Could fuel temp be related as the lines run along chassis near exhaust)
Could this contribute to thermal runaway at highway speeds?

Cheers

[celicapain]

I think that's the first UZ to Hiace conversion iv'e heard of-noice!

Regarding you question could you clarify the noise that your hearing?
Also, could you clarify what kind of fuel system plumbing you have.

I don't have enough information to guess what the problem is, but I can think of a few tests that may narrow it down.

1- Test start from cold early. Do several quickly while the engine and fuel system are cold.
2- Get car up to temperature and stop the engine. restart it quickly and note how the fuel system sounds. Then turn it off, leave it for 15 minutes to allow heat soak then restart.


Its unlikely that you have enough heat going into the fuel system to boil the fuel while it is circulating. It takes a lot of heat to vaporize fuel under pressures as found in the feed side of a EFI system.
If fuel IS being vaporized in the return line then it shouldn't matter as it can vent back into the tank. I would guess its most likely your fuel pump, as that's the only moving element in your fuel system(with the engine off) and thus the most likely cause of any noises that your hearing.
The other possibilities I can think of would be hydraulic hammer if you had a restriction in your return line, but that would be pretty unlikely IMHO

[davewanna]

Cheers for the response. It's not what I'd call a great idea and I probably wouldn't do it myself but it's interesting and it's fun to drive!

The sound is like aerated liquid in a hose, hence why I'm guessing that's my problem but I maybe barking up the wrong tree. Think if you have a kink in your garden hose and when you turn the tap you can hear the air/water rushing through the kink, then when the air is gone and it's water only the noise is much quieter and more consistent.

Aswell as the sound I can feel the vibration if I put my fingers on the return steel pipe from the regulator. Inlet pipe and injector rail doesn't seem to vibrate.

Intank EFI pump (Not sure what it is) that doesn't have a speed controller that I know of. I may find one hidden somewhere yet. Steel fuel line runs up the chassis rail roughly 100mm from the exhaust. Inline EFI filter on the rail with an EFI rubber hose off one end that is showing distinct signs of heat stress with cracks and colour change. Definitely something I want to change/add heat shield.

After a decent run on the highway on a hot day when I stop I can hear the pump howling. I've had this same noise under same conditions in the past on my 3rz converted hilux with EFI pump, surge tank, and filter mounted to the chassis rail. A long run on a hot day would cause the pump to howl, someone told me it was the fuel aerating due to temperature, pressure, and flow speed.

Regarding the cold start tests, I have done a number of them and it seems same every time. The sound seems a lot louder than in the past but I'm worried that I'm paying more attention to a sound that I just didn't notice before. The cold start prompts me to something else that it's done ever since I bought it. Most mornings, first start it will fire quickly, and then settle to a low lumpy idle for about 10 seconds. Never stalls, doesn't even splutter, just sounds like a low idle V8 with a cam. IAC valve is working and opens right up to try to bring the idle up, but stays low for roughly 10 seconds before it all of a sudden revs up to around 1600rpm and the IAC valve closes up a bit to bring it back to a normal smooth idle. Never does this any other time, only first start of a morning. Ambient temperature here at 7am is around 30degrees so it's not like it's proper cold or anything