I once blew the knock sensor on my old (thank the gods I sold it!!!) '03 S-Type simply by opening the hood while it was raining (ok, a good Tennessee rain, but still...). Fortunately for my long-standing desire to replace the intake manifold gasket, this was the sensor under the manifold (::yaaay...:.

I've never had a good reason to "wash" my cars' engines, but applying some Turtlewax Trim Restorer to the black plastic covers makes everything look nice-nice, even if the engine block is a bit grimy. And it can be good to keep those dark, oil-stained areas as-is so you'll know where to watch for the inevitable S-Type oil leaks in the future.

 

I don't have or get any oil leaks?

120K on my 2005 STR.
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Nor I.......

 

Funnily enough my knock sensor bank one was showing a strong signal, engine management light and occassocca restricted performance, but after a car wash (exterior with pressure washer) it cleared. Very odd.

 

Well I'll just add my experiences on everything from a 77 Maserati that had its engine compartment washed regularly and NOT voluntarily all the way up to my 99 Suburban and yes the 2005 STR.

I never wash an engine cold or hot but warm. I begin with a degreaser which is usually paint thinner as applied with a compressed air siphon gun. This is done with car over a thick tarp and then entire compartment is blow out extensively with compressed air. Next I use a mixture of hot water and simple green followed by plain hot water. All with the syphon gun. NO PRESSURE WASHER.

I'm pretty circumspect about hitting electrical areas, no computers or fuse boxes directly and if necessary I place something ahead of time to block those areas. Some additional hand work is usually needed during each of these steps.

I've had several high speed CV boot failures on one car and that gawd awful grease is a real SOB to clean up but this method was flawless in dealing with it.

Because I heat the entire engine compartment up ahead of time and then allow sufficient cool down time I think this causes any potentially harmful liquids to evaporate rather quickly. Lot's of forced air pressure also helps with this.

But do mind the electronics guys.

 

Engine temperature is a hit miss when washing. Hot or warm engine increases the odds of condensation inside electrical connectors since they cool quickly and the engine heat makes humidity/steam.

I usually do a cold engine wash with cold water, blow dry with compressed air to get rid of the bulk of the water, then immediately drive in hopes that the moving air will blow the humidity away as it's being made so it won't condense in bad places.

At the International truck dealership I worked at all engine washing was done on idling engines with a hot pressure washer, don't recall any issues but these things had pretty robust sealing and much fewer sensors than the average car.

I've washed several engines since the STR without issues 'till a few days ago. I washed my Excursion 7.3 diesel and water got into a connector for the injection pressure sensor. The 'failure' caused by that wet connector was that it supercharged the thing. I rolled onto the freeway and hit the power and the thing rocketed as if I was in the STR, nutty. It also had lots of other odd running issues under light load. When it finally dried out things went back to normal, but it was an exciting experience having a sluggish 4 ton soccer mom SUV suddenly turn into a race car. It has 425k miles so I forgive the sensor seals not being perfect.

 

I don’t wash my engine bay anymore but after every rainy night I get code until warmed up. It really drives reasonably well in normal traffic with the RP. Once the code is cleared you can open it up to triple digits.

 

I will not risk washing the engine bays of either of our Jaguars. I wipe them down with old towels, a small amount of silicone spray, and plenty of elbow grease. Too many potential electrical problems can arise by introducing water into these Jaguar engine bays....

My 1999 Dodge Ram pickup is a different story. That 5.9-litre engine can take a good washing and I have done so a number of times over the nearly 18 years I have owned it. But never with a pressure washer - only a carefully-streamed garden hose after spraying the warm engine with half a can of Engine Brite and letting it soak in for ten minutes or so....

 

I've actually done it twice on my 05 STR as described earlier and zero issues.

When my engine oil and tranny cooler hoses/lines both gave out there was just too much mess to try and hand wipe everything. MY car is a lot more crowded than yours!

The mineral spirits does get rid of a lot of grease and then only simple green & H2O will get rid of the actual dust and dirt.