I use Castrol Engine Degreaser not because of Castrol but because it was in the closeout bin in Autozone haha.I use it on my 93 NX no problems.Just make sure all your lines are tight and have no leaks.Which they shouldnt.Yet.....................
Its ok to hose off your engine, so long as you don't soak the electrical components too much. The Murano's engine bay is very tight, so I am not sure if you can put plastic draping over the alternator, which is what I usually do. BTW, how dirty outside the engine has no bearing on how it performs. I know you like to keep it clean, but you may be accelerating rust on unfinished surfaces (such as the exhaust bolts, etc...) if you hose off the engine bay.
That said, I admit with my Maxima, I hosed off the engine every so often and even at 100,000 miles, the engine is clean as the day I drove it off the showroom floor. I use the cheap stuff, Gunk's Foamy Engine Brite, its like $2-$3 can and works great. Make sure you check your local laws on disposal of the wash liquid though, as it does contain petroleum products. If you want to go environmentally friendly, liquid green (i believe thats what its called) is the way to go.
The sooner you add engine cleaning to your regular maintenance routine, the easier it will be to keep it clean over the years.
Don't worry about getting anything wet in the engine compartment because the engine was designed to get wet, including the alternator. I've been washing the engines in my cars for many years (completely soaking the compartment) and have yet to have one not start. I have already washed my MO's engine a few times using the method described below with great results.
NOTE: Wash your engine before washing your car because there will be overspray onto the body.
Oh, DO NOT use those high pressure sprayers found at DIY car washes. You could likely damage something.
1) Start the engine and get it warm. Do not let it get scorching hot. Turn the engine off. This will help the engine dry more quickly. If the engine is already very hot (from driving), just be careful around hot spots (radiator & hoses, engine block, etc.).
Remove any loose debris (leaves, twigs, etc.) by hand before wetting down the compartment, especially around the cowling area.
2) Hose down the entire engine compartment including the cowling by the wipers and the underside of the hood. Don't use high pressure, though. In fact, just let the water flow out the open end of the hose (without a sprayer attachment) so you get a lot of flow without a lot of pressure. If you need some pressure (like when spraying the underside of the hood), use your thumb to control the flow out the end.
Also spray the area behind the grill, in and around the radiator area. You should use some spray pressure here to get into the nooks.
3) Wash the engine by hand. Use a bucket of regular car wash soap + water unless you have a heavy accumulation of grease and oil sprayed over your engine compartment. Since your MO is probably less than a year old, there should not be any of this unless you have a leak somewhere (then you might also have an engine problem and may need to see your dealer).
If you have a mild build-up of oily grime, you can use dish soap (like Dawn). Just remember that it will take off any wax on your MO's paint job if you get it on the body.
Engine cleaners (Gunk, Engine Brite) contain strong solvents which are great for tackling heavy grease and oil (like in older, poorly maintained engine bays), but they can also take printing off labels and are not great for your paint (from overspray during the rinse). While they should not damage the paint (unless the paint is hot), they will take off any wax. One exception: if you have a lot of grime in areas you cannot reach, use might want to use one of the spray-type engine cleaners.
Use a small terry towel soaked in the soap+water solution, carefully wash off the exposed area (hoses, covers, around the fluid containers, firewall & wheel well area, etc .). Also get the underside of the hood, along the cowling by the wipers, and the area around the hood latch and grill. Don't use a sponge because there are a lot of sharp points in the engine (hose clamps, cable holders etc.) that could tear into it and leave bits behind. Those points can also tear into skin so be careful!
3) Rinse off the compartment with a strong flow of water (lots of water, medium to light pressure).
5) With a clean towel, wipe off the engine and as much of the compartment as you can reach. Carefully get behind hoses and wiring without pulling them from holders, etc.
NOTE: Be sure to completely dry the top and sides of the battery with paper towels. That way you do not spread any acid (if any) around the rest of the engine compartment. You will also clean away any potential conductive paths between the terminals.
6) Dress hoses, wires, plastic covers, etc. with ArmorAll, if desired. Don't use it on hot surfaces (though it is ok on radiator hoses).
Also, lube the front latch contact surfaces with white lithium grease. Do not use simply use silicone spray because it can wash away any grease lubrication. If the grease is black and dirty, wipe it away with a paper towel and reapply new white grease. Apply grease to the contact point on the latch hook on the hood, too.
Lube the hood hinges with spray lithium grease (again, no silicone spray).
Wipe down the chrome shafts of the pressurized hood support pistons with a paper towel soaked with a little silicone spray. With that same paper towel, wipe the rubber bumpers that support the hood when closed. (note: silicone spray will take printing off any labels so be careful)
Fill-up your windshield washer container while you're in there, too.
Start your engine and let it get hot to dry off the rest of the block. Then finish washing the rest of your MO.
I have been using Simple Green on all my cars for about 15 years now. I used to use gunk but it is just way too strong and dulls some metal parts. I spray on simple green when the engine is still cold and let it sit for a few minutes and for the areas that are dirtier, I use a brush and just brush it a bit, then just hose it off with lots of water. I have never had any problems with my cars not being able to start afterwards. Of course, I wouldn't do the same exact thing on carburated cars. I also use my metro vac in reverse to blow most of the water off and wipe the rest dry. I usually do this every 3 months or so and is easy to keep it clean.
One other benefit is that simple green is much more environmentally friendly. The overspray from gunk can easily damage your paint if you don't catch it.
Hey! SimpleGreen is a great idea! Plus, you can spray it into the spots you can't reach. If using SG, I would not warm-up the engine and leave it cold as lingan suggests since the SG might evaporate too quickly for it to act on dirt and oil.
I would still give some surfaces a quick wipe with a wet towel (sprayed with SG) because some road film may not come off as easily. You may also want to warm up the engine with the hood open after cleaning and drying, just to dry off the block (otherwise the smell of the evaporating cleaner and water will permeate the passenger compartment through the cowling then next time you drive around).
Just be little careful with overspray onto the body since SG may take off the wax, but it definitely will NOT hurt the paint like Gunk or other harsher cleaners.