Ask a Mechanic: Why Pressure washing an engine bay is not a good idea. 

In today’s column we learn why a parking light being out may not just be because of a burnt bulb and why you should not pressure wash under your vehicle’s hood.

By Nida Zafar Wheels.ca

Aug 21, 2021 3 min. read

Article was updated a year ago

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Every week, we take your questions about what is going on under the hood of your vehicle and pose them to a knowledgeable mechanic in the Greater Toronto Area. In today’s column we learn why a parking light being out may not just be because of a burnt bulb and why you should not pressure wash under your vehicle’s hood.

Dear Ask a Mechanic,

The front driver's side parking light on my car is out. I’ve checked thoroughly and it’s not blown out and doesn't seem to be a faulty bulb. Headlights, taillights and the three parking lights are working fine. I’m looking for a professional opinion. What are your thoughts? – Burnt out

Atif Mohammed, co-owner of Humble Autohaus in Scarborough, said that if the light socket is in good shape, it’s possible the bulb is burnt and needs to be replaced. But, he added, a quick look isn’t enough to know the whole story. Mohammed said you should have a professional examine the issue and study the wiring diagram for the parking light circuit on the driver’s side of the vehicle. He said there are two possible reasons for the outage: either there’s a problem with the power wire or an issue with the ground wire. After pinpointing which it is, a professional can refer to the diagram and follow the wiring to test and ensure its integrity, fixing it as needed.

Dear Ask a Mechanic, 

I want to clean the engine bay on my 2004 Suburban. What’s the recommended procedure for cleaning the block and intake manifold? There are no major leaks going on, just typical buildup due to not cleaning it for a couple of years— Buildup

“Cleaning an engine bay is not a good idea,” Mohammed said, especially by pressure washing.

Both electronic modules and the engine computer are usually located under the hood of the vehicle. Pressure washing can force the water to penetrate the weather-pack seals on wiring and other electrical elements. If trapped, this water can buildup and cause corrosion. It can also get into the ignition system and cause it to misfire. As well, you should also avoid using harsh chemicals to degrease the engine, as these could damage components of the vehicle including its painted surfaces. A better cleaning technique, Mohammed said, is to blow away the dirt using compressed air. If you insist on using water, he said it should be a low-pressure wash and all electronic parts of the vehicle should be properly covered to protect them. You should also ensure all parts that are washed are properly dried afterward.

Ask a Mechanic is written by Nida Zafar, a reporter at The Pointer who grew up in a house full of mechanics in Scarborough, and occasionally poses your questions to her dad or brother. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle. 




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