Vapor Lock 2013 Edition

[Gunn]

And so, the saga continues...

Over the last couple of years I've been battling vapor lock in my twin 4.3MPI's. I've gotten better about dealing with it and preventing it but in some circumstances it's hard to avoid a scenario that will make it happen (re-fueling at a fuel dock, fishing).

Over the winter, I replaced both of my bilge blowers with higher CFM versions to move more air. And I also replaced the engine checkvalves that are installed in the water line right before the fuel cooler, as this fixed the issue for another member here.

And then last night I ran the boat for the first time this season. I ran for one hour. Got to my home dock and shut down. I waited for 30 minutes and then started both engines. Everything seemed fine for a minute or so. And then the port engine died. I tried to restart, it barely ran at a couple hundred RPM, and then died again. Tried to start again, but wouldn't even fire. Classic vapor lock.

Since I was now at home, I could do a little more detective work. I grabbed my IR thermometer and started checking temperatures. The hottest temperature I recorded was 133.5 right at the entrance to the fuel cooler down low on the rear of the engine. The fuel lines running by here and up to the engine were not much cooler.

I then grabbed my fuel pressure gauge and put it on the shraeder valve behind the air intake. When I moved the start button to the on position, it showed about 8-10psi. Obviously not the 38-40 I should be seeing. I then used the purge button to purge the gas into a container. Lots and lots of bubbles. I repeated this process a few times, reading fuel pressures from nearly nothing to 10psi. I then left the switch in the on position and pressed the purge. I ended up purging about a cupful or so before the pressure started to rise. I then cycled the pump and hit over 40psi. I did it one more time and the gauge rested on 40psi. I then purged, cleaned up and removed the gauge and put the flame arrestor back on.

The engine started right up and ran nicely for 5 minutes or so before I wrapped up and went in for the night.

So....where to go from here? This is the second time in a row that the port engine has vapor locked when the starboard has not. Early last year I suffered a fuel pump failure on the starboard engine and replaced it. No vapor lock on it since. Coincidence? Could the fuel pump itself have anything to do with this?

Also, why the 130+F temperature right past the check valve and right before the fuel cooler? In the minute that the engine does run, shouldn't this have been nearly sea-water temperature? The checkvalve is supposed to prevent hot water from the block from moving back down and into the fuel cooler. I'm confused by this temperature. My engine runs for a minute, so I'd think it would have sucked up enough sea water (65F) to avoid these kinds of temperatures here. And yes, I did replace the checkvalve in the correct position; there's actually on one way to install it (different size hoses).

At least I have learned of a way to overcome it quickly now with my fuel pressure gauge. But I'd rather not have to revert to performing this with a few guests on board, or after a refuel and am stuck at the fuel dock!

Thanks,

Tom

 

[MarkIC]

Hi Tom

Thats a shame as a new check valve fixed it for me.

As you are still recording high temps at the fuel pump after shut down I'd almost suspect the new check valve is not working properly but this would be unlikely. The temps should not increase that much though. Is it easy for you to lightly clamp the cooling water hose off before or after the fuel cooler after a shut down? A small g clamp and two pieces of 3/4 x 3/4 timber would work. Dont over clamp as you dont want to damage the hose its just another way to positively stop water back flowing straight after you shut down.

Then wait the 20~30 minutes, remove the clamp and see how she starts up.

Another option which is only a mask of the issue is to plumb one of your blower supply air lines to supply air right to your fuel cooler area although I'd rather fix the temp issue than use the blower to solve the problem, will still help though.

A couple more tests, when you fit your fuel pressure gauge and the pump turns off with 40psi showing does the pressure remain or drop away quickly when the pump stops. If it falls away quickly I'd look at running some injector cleaner through your fuel system as well as possibly replacing the fuel pressure reflief valve that bolts to the top of the fuel cooler however as you are seeing the target 40~43 I dont think the relief valve is the issue. If the fuel system is good the fuel pressure should remain unless you have a dribbling injector etc and this pressure keep the fuel above its vapour pressure so it remains as a liquid.

I hate bleeding off fuel in a boat, potential risks are high if you spill any so please take extreme care when doing this.

All the best, I hope some of the above might help you sort this out.

Regards Mark

 

[Woody]

Gunn, one of the other times this came up I poked around on the net. I recall reading that sometimes merc put a check valve ahead of the cooler so the warm water definitely can't mix backwards. Maybe worth a try.

 

[floriduramax1]

Gunn, it's my port engine that is the worst as well. My starboard will fire up, albeit, a little sputter here and there but will run none the less. My port, I have to give over half throttle at start up every time after I run hard and shut down for 15 mins or more. I have the aux pumps and used clear line from the pump output to filter and tested. I had no bubbles and maintained 38-40 psi constant. Mine was worked on by 4 different Merc techs under that extended warranty so I have just about everything brand new and nothing has made even the slightest difference on my port engine. It's almost like the ecm needs a reflash!!!

 

[BOATER JOHN]

Gunn, it's my port engine that is the worst as well. My starboard will fire up, albeit, a little sputter here and there but will run none the less. My port, I have to give over half throttle at start up every time after I run hard and shut down for 15 mins or more. I have the aux pumps and used clear line from the pump output to filter and tested. I had no bubbles and maintained 38-40 psi constant. Mine was worked on by 4 different Merc techs under that extended warranty so I have just about everything brand new and nothing has made even the slightest difference on my port engine. It's almost like the ecm needs a reflash!!!

have you tryed switching the ecm from one motor to the other?

 

[capecodcruiser]

I would just replace the pump to be safe and eliminate that issue. Boat engines are not all that different from automobile engines. Can you imagine having these issues on your daily driver?? I fully understand the fuel cooler, etc., but the system is basically pretty simple. Also, with the bubbles you are getting, I would go back through the whole system and to be sure all clamps, fittings, etc are tight and secure. Any thoughts on pressurizing the fuel tank and to take soap/water solution to all joints/fitting to see if you are getting any bubbles??? Just a thought. Low pressure obviously.

 

[floriduramax1]

have you tryed switching the ecm from one motor to the other?

You know...,,NO!!! I guess that would be a great place to start...lol. I think I will try that this weekend! I don't know why I didn't do that already...duhhhh

 

[Gunn]

Thanks for the replies.

Mark, that is a good idea to pinch off the hose temporarily and see what happens. One of the things I want to do next is to monitor the temperature in this area from engine start onward. Then shutdown and continue to monitor and see how and when it climbs.

As far as the fuel pressure, once I got the air out and the pressure came back it was rock steady at ~40psi and never wavered even after I moved the switch to the off position...it does maintain the pressure.

Woody, with my 4.3MPI, I have the single-point drain system. In this system and the 3-point drain system, they have a check valve installed immediately ahead of the fuel cooler as seen in this diagram (part #2). This is the valve I replaced. And I did test the new one before I installed it. I held it in the proper orientation and submerged it in a bucket of water up to near the top inlet. No water seeped in, even at an angle of up to 30-45deg. It is mounted nearly vertical on the engine.

The check valve that Mercruiser frequently mentions in their Vapor Lock bulletins is installed on engines with 7-point drain systems and is Part # 13. I don't have this checkvalve as it is not possible to install. But this setup doesn't have my check valve. Having one or the other should solve the problem of hot water backflowing to the fuel cooler.

I was re-reading the 2001 Mercruiser Vapor Lock bulletin and they specifically mention this:

Under the hottest outside air temperature condition that the boat will be operatedin, the temperature of the fuel being supplied to the engine shall not exceed 110F
(43C) at any location between the fuel tank and the engine’s fuel pump

My 130F measurement sure blew that number.

I would just replace the fuel pump as the next step, BUT...it is not cheap (>$300 IIRC) and even worse, it is a royal pain to remove. In fact, as hard as the starboard engine fuel cooler was to remove, I wonder if it is even possible to remove the port side without lifting the engine??? The fuel cooler is located on the left side of the engine (as viewed from behind the engine looking towards the bow). The starboard side is nearer the bottom of the boat and so there is more room under the cooler there. Has anyone ever replaced (or had replaced) their port side fuel cooler? I'd like to hear if it's even possible...

Thanks again for all the responses. If anyone has any other ideas wild or otherwise, I'm all ears. Someone mentioned to me (non-boating guy) adding an electric water pump kit. Never heard of one for marine/Mercruiser engines. Would it be a bad idea to circulate raw water with the engines off in regards to the exhaust manifolds and water ingestion?

Tom

 

[MarkIC]

Hi Tom
I replaced my pump only with an aftermarket marine Mallory one that fits our cooler type. I don’t know why Mercruiser wants us to replace the whole pump and cooler as my cooler was in perfect condition. I replaced all o-rings and seal when replacing the pump.

Here’s a link to the pump I purchased
http://www.ebay.com.au/itm/121046622964

It was difficult but possible and took me a couple of hours to remove the pump and about the same time to re-fit. I expect I would get it done in about 2 ½ hours now if I had to do it again and space was cramped but I’m not sure how my boat compares to yours for space.

As yours is pumping to and maintaining pressure I don’t think the pump is your issue.

The fact that the pressure was rock solid once you removed the fuel vapour by bleeding the system off and everything was perfect also confirms this. These pumps cannot pump vapour/gaseous fuel with any significant effect or pressure, they might pull enough through to help prime a new filter but not at any real pressure due to the internal clearances within the pump, they need fluid to work as designed. Once liquid fuel is present it can achieve its designed 40psi and with pressure the boiling temp increases so the captured vapour is turned back into liquid. If theres still a little vapour in the fuel system after the pump this is quickly discharged through the fuel injectors which will pass gasoline vapour at much higher rates than liquid gasoline in the first few seconds of running.

I’ll also try and find some info on Gasoline and vapour pressure so we can have some info on boiling point temp vs pressure at 43psi but it’s proving to be more difficult to find than I expected, back to the text books I guess.

To monitor temps while running can you get hold of a multimeter that takes a thermocouple input, most automotive ones do? This would be perfect and you can feed the thermocouple tip inside the plastic fuel cooler housing to monitor the cooler temp over a range of running and stopped conditions. If you can tape it to the cooler with aluminium tape that would be perfect to get an accurate heat transfer to the thermocouple. I’ll do the same with my engine and report what info I get next time out.

I’d also be concerned with pumping cooling water through the engine with an electric pump and subsequently to the exhaust without the engine running. Mercruiser have a technical bulletin advising to flush engines at 1300rpm to ensure enough exhaust flows to prevent water ingestion so having no exhaust flow would be a real concern for me.

The faulty check valve doesn’t make sense since its new but I can’t see how the temp should rise so much without engine water back flowing through the cooler especially since other surrounding fuel lines etc were at a much lower in temp.

All the best with it, I'm sure we'll solve it soon

Mark

 

[magstang1]

Would it be possible to add another heat exchanger?

i realize the system should function as engineered, but at a certain time it's best to just make it work reliably.

I really have no knowledge of your fuel system so I apologize if my question is way off base. It was just a thought I had.


Good luck!

 

[Molson]

What about wrapping the lines and cooler with something like exhaust wrap. We used to wrap the headers and down pipe on our race cars to stop from burning the drivers feet, I wonder if that would help keep the heat out of the cooler and fuel lines.

 

[kkalsch]

Tom...i have the same boat/power package year and model as you...last year the Water Distribution housing started to leak -when I removed the hose #10 (on your first diagram) there was positive pressure of water flow -(like sink your boat) I had to block the hose so I could replace the housing -our boats sit so low in the water -I am not so sure hot water could travel back to the cool fuel -An easy test would be just twist your drain rod up and see if the water ever stops-mine doesn't -unless the boat is out of the water-but hay that may be a quick way to cool the fuel-no fun intended

 

[Gunn]

Thanks for all the suggestions. I will have to see if my multimeter is capable of a thermocouple. I'm thinking it is not, since it is not a very expensive model. But if so, that would be a nice feature and a good idea to see what is going on.

The positive pressure flow on that line is very interesting. When I put the boat in the water next time (it's up on a lift now), I will have to open the drain valve and see what happens. And if it is a non-stop flow of raw seawater, then that would most definitely be a super easy way to cool the fuel cooler! Obviously, not my preferred "fix", but a better solution than purging raw fuel when drifting in the sea.

More testing will most likely be this weekend...

 

[MarkIC]

Hi Tom, the multimeter I purchased wasnt that expensive at around $80 and had a number of engine type functions like rpm, thermocouple etc etc. and has been great over the 5 years I've had it.

Also the thermo couple that comes with it has flat dual core wire that is small and flat enough to feed into the water flow by having it enter in at a hose junction to be internal within the hose and seal off ok for testing when you tighten up the hose clamp with minimal if any leakage.

Not sure where you would get one near you as I dont think dicksmiths are in the USA but here's a link so you can see the features etc.

http://dicksmith.com.au/product/Q1585/automotive-multimeter

I'd be happy to send one your way but would expect postage from Australia to be around $50

Cheers Mark