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Why is My Car Overheating?

Post on January 22, 2019 by

This month, we’re going to answer the question:
Why is My Car Overheating?
Or, why do I have to keep bringing my car back in for overheating after having it fixed?!

This is a very valid question, and more common than you might think. To get an understanding of this, we first need to understand some basics of how the cooling system on an engine works compared to other systems.

1. Unlike all other fluids on your vehicle which are mostly oil based and drip out slowly, coolant is water based and leaks out rapidly with rare exceptions. Temperature will also play a big role here; cold or hot outside temperature will cause seals to swell or expand, making leaks more or less pronounced. Therefore, it is not uncommon to see a cooling system leak develop in the winter with the seasonal change in weather – colder weather will cause seals to shrink and leak out more.

2. Your cooling system works under pressure ranging from 14-28 psi constantly depending on your vehicle. When a problem or leak starts to develop, the system may start operating at a reduced pressure due to a leak for some time before you, the driver, notice. Now, after a repair, the newly sealed and properly functioning system is now operating back at full pressure. This in turn, can stress weak and/or aged components that have not been used to this pressure for some time before getting a vehicle repaired back to the correct operating pressure. This is similar to a dripping faucet in your home that you don’t think much of for some time, and finally after getting it fixed, another issues springs up. This is why, sometimes a second visit is required to the shop for cooling systems even if everything was done properly at the time and checked out over a 5 to 15 mile test drive.

3. Damn cheap plastic! That’s why I’m having problems, they aren’t using metal like the good ol’ days! WRONG. Did you know: most BMWs have radiators with plastic tanks. These do not fail often, and when they do, it is typically a result of extreme over pressure or extreme age. However, most 5 and 6 series have all aluminum radiators, which often leak due to chemical electrolysis of the metal. There is a reason the engineers chose plastic polymers in certain cooling system components. A few reasons are: plastic polymers are actually stronger than a metal counterpart would be, they prevent chemical electrolysis, and in the case of a failure due to extreme pressure, in theory, these plastic components will burst before your engine cracks or warps.

4. Time: a vehicle that is 10 years old does have components that are more brittle and aged and although they may have been working fine for some time, after pressure is back up at operating specifications, these components can fail as we’ve eluded to in point #2. This is why many shops or dealerships often quote entire “kits” or “packages” for the cooling system. While we do not believe that shotgun approach is in your best financial interest at Ultimate European Repair, we do make sure we explain why select crucial components are required with repairs and have the discussion with our clients on what to expect with a repair and the best options for your vehicle based on your use.

5. Unfortunately, repeat visits sometimes boil down to incompetency. Perhaps most overlooked is a proper diagnosis. With some exceptions, it is the policy of Ultimate European Repair to perform cylinder leakdown and compression testing on an engine anytime it is overheated. This is because we want to look out for your best interests: No matters how many radiators, hoses, water pumps, thermostats, etc. one throws at a car with an engine that is internally damaged from overheat, the vehicle will continue to overheat and damage the new components. It is only fair for you, and us, to know upfront if your engine internals are OK, or if they are damaged from an overheat, BEFORE proceeding with any repairs. This is because often times, internal engine damage essentially totals the value of the car.

Posted in Blog

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