Oct 122014
 

If you know me or my blog, you know I watch Lake Powell. Most of my posts are about the water level increase expected each spring and early summer. But many boaters have reported weather problems at the lake that weren’t related to dust storms, thunderstorms or wind storms. Triple digit temperatures are a common occurrence on Lake Powell. The high temperatures can cause engine problems.

Waterskiing at Lake Powell

Waterskiing at Lake Powell

On of the intended benefits of fuel injection was to prevent vapor lock. The gut reaction of most “gear-heads” and marine mechanics is that a fuel injected engine can not suffer vapor lock. I’m now a believer that there is a mechanism for vapor lock in a marine engine.

Marine engines run in a tough environment. The stern drive motors are typically inside a small engine compartment with limited ventilation and exceptional noise insulation. It’s a great environment for containing heat. The lower unit of the stern drive takes up fresh water and pumps it to the engine and support systems. It’s a great way to cool a motor while it’s running. But when you shut down a boat’s engine, there isn’t a natural heat release path. You can run the engine compartment bilge blowers to provide air flow. But there is no radiator like in a car. In the Lake Powell’s summer temperatures, blowing 110 degree air over a 155 degree engine has little effect.

To protect the fuel, a fuel cooler is a part of the cooling system. The fuel cooler’s intent is prevention of fuel vaporization due to high engine compartment temperatures. The water comes in from the outdrive, flows through the power steering cooler, then the fuel cooler, before going to the engine’s thermostat housing. This doesn’t work after the engine is shutdown, either.

Over the last few years our boat driving habits at the lake have changed. We used to spend lots of time on the beach with brief runs for water-skiing or wake boarding, or sightseeing. Now, we tend to do longer runs with plenty of canyon exploring and trips to Rainbow Bridge with friends. This means we run our engine longer and the compartment and engine gets thoroughly hot. Here is a temperature profile of the engine during a summer weekend trip. I measured the temperature on the top of the thermostat housing lifting eye. So, it wasn’t in direct contact with the housing or engine.

Engine compartment temperature profile, July 18-19, 2014.

Engine compartment temperature profile, July 18-19, 2014.

The heat build up is fairly quick. Idling the engine after a run provides a fair amount of cooling. But after shutting down the engine, the cool-down is much slower. Opening the engine hatch provides a better cool down of the top of the engine. Shorter runs result in a much faster cool down. We had to open the hatch because the engine wouldn’t start; we hypothesized vapor lock. But the engine compartment temperature had cooled much at this point. Shouldn’t it have started?

There is a theory about some marine engines. The theory is that some of the engine cooling water flows backwards after engine shutdown. This takes very hot water out of the engine and back the way it came. The first stop on the way out is the fuel cooler.

My son and I tried to replicate the outcome. We took our boat on a long, roughly 40 mile round trip. We went straight back to our slip at Wahweap Marina and shut down the engine as quick as possible. We watched the temperature on top of the thermostat housing lifting eye, and the air temperature inside the fuel cooler box, just an inch or so away from the real heat exchanger.

Thermostat housing and fuel cooler temperature

We watched the fuel cooler temperature quickly move from 101.5 degrees F to 121F at 15 minutes, and hit a top temperature of 124F by 30 minutes. At 45 minutes, we thought the temperature had stabilized and attempted to start the engine. It turned over, but didn’t start. We took a video the fuel being injected at the throttle body when cool, and again when it failed to start.


The fuel spray in the hot video is quite different with spurts, drips and gaps in the flow. The cool fuel spray is well atomized. What a difference!

On other trips, I tried to measure the temperature of the cooling hose that allows back-flow to the fuel cooler. Since the data logger I used had a self-protection turn off at 140F degrees, it only produced a few minutes of data as the temperatures climbed above 140F. Back-flow was the likely issue.

Mercruiser is the manufacturer of my engine. They have provided a tech bulletin about this vapor locking issue on their V-8 engines.

Mercruiser Vapor Lock Tech Bulletin

One of the solutions Mercruiser gives is to insert a check valve in the cooling system to prevent back-flow. I opted for this option. I installed the check valve in the cooling line between the fuel cooler and the thermostat housing. When I removed the existing hose, I found that it was mostly empty. To me, this validated the back flow problem as an issue. The top part of the engine coolant drained out via the fuel cooler. With the included instructions, the valve was remarkably easy to install. An experienced mechanic could do it in probably five minutes. I invested 45 minutes. Here’s a picture of the installed valve.

Cooling line check valve installed. Blue with yellow in the lower right.

Cooling line check valve installed. Blue with yellow in the lower right.

To test the repair, we did a high-speed run to Rainbow Bridge. When we shut down the engine, I watched the fuel cooler temperature. At 15 minutes, the temperature had dropped by 0.3 degrees. In other trips since then, it has occasionally increased, but never above 103F.

Every pump has a low pressure intake, and high pressure discharge. The fuel pump takes it suction on the outlet of the fuel cooler. The pump’s suction can vaporize the heated fuel, even if it is below boiling point. I wanted to record this some place because many boaters at Lake Powell to get hit by this phenomena.

 Posted by at 6:35 pm
Oct 062014
 

The remnants of Hurricane Simon are on their way to Arizona. The big question is still around which path he will take. The Navy NoGAPs computer model has the bulk of the storm going to the west and north of Flagstaff. The GFS model has the storm going to the south and east of Flagstaff. [...]

 Posted by at 5:27 pm
Oct 042014
 

Something new for my blog readers. I’m going to occasionally add reviews for product that are weather related to my blog. First up is the new WR-299 Weather Radio. Please watch the video for details. This is a great compact emergency weather radio that offers AM/FM and Weather bands. It also have an Alert Mode [...]

 Posted by at 2:19 pm
Sep 302014
 

I’ve struggled the last few days with a broken internet connection, malfunctioning iPhone and a rainy weekend. The weekend struggle was the wonderful malaise that can hit Arizonans when it rains all day. Nonetheless, the Climate Prediction Center issued new outlooks for October and the 3-month period October to December. The outlooks point to El [...]

 Posted by at 7:10 am
Sep 272014
 

A strong cold front is crossing Arizona from west to east today. While the moisture is coming from the south, the cold front is a winter weather phenomenon for Arizona. We are expecting fast-moving thunderstorms with heavy rain and other severe weather. This is reminiscent of the storms on October 6, 2010. The National Weather [...]

 Posted by at 7:02 am
Sep 152014
 

Watching the GFS animation for the next 7 days this morning, I noticed a curious flow in the precipitation pattern. This flow reminded me of our last interaction with the remnants of a hurricane. Hurricane Norbert’s moisture missed us by traveling barely south of us. Next up for us are the remnants of Hurricane Odile. [...]

 Posted by at 6:34 am
Sep 112014
 

The newest 6-10 and 8-14 day precipitation outlooks show wet conditions continuing. We should be dry today and Friday. There is a chance for showers over the weekend and into early next week. Sometime in the second half of next week, tropical storm, soon hurricane, Odile will deliver more moisture to Arizona. Tweet

 Posted by at 6:28 am
Sep 092014
 

Mother nature decided to blow the forecast away. There was a ton of moisture in Arizona’s atmosphere. Below is an image from Intellicast.com that shows an estimate of daily precipitation based on radar imagery. If you compare this image to from the National Weather Service, you can see that things didn’t turn out to forecast. [...]

 Posted by at 6:51 am
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