What might seem routine for an experienced auto repair shop - replacing coolant thermostats - is not as straightforward as one might think. In truth, this standard repair can be quite challenging. So, here are two crucial tips right off the bat:

Never use sealants

Always bleed the air out of the cooling circuit

Three Strong Reasons Against Pastes

So, why shouldn't sealants be used on thermostats?

 

Seal and paste don't mix

Thermostat seals consist of a complex mixture of materials. Often, they contain elements that aren't oil-resistant. However, sealing pastes typically contain mineral or synthetic oil components. When these come into contact with the thermostat seal, the seal swells and gets damaged.

Making what fits, unfit

The groove for the thermostat seal and the dimensions of the seal itself are precisely matched. There's no space allotted for additional paste. If it's applied nonetheless, the volume to be accommodated increases, jeopardizing a perfect seal.

 

Beware - Clogging in the cooling circuit!

Often, so much sealing paste is used that some of it enters the cooling circuit. It's particularly disastrous when paste particles swell, impeding the flow of coolant. Sometimes, they even get stuck in the thermostat, preventing it from opening or closing correctly. The result? Inadequate heating and cooling performance.

Therefore, we at MAHLE Aftermarket strongly advise against using sealing pastes.

Let that air out!

But what if temperature issues arise post-thermostat replacement? First things first: bleed the air. If a temperature problem occurs after replacement, it's typically due to air in the cooling circuit. So, before replacing the newly installed thermostat, make sure to carefully bleed the cooling circuit!

 

The topic of "Why and how to bleed?" is also covered in our article titled "Highly Recommended".

 

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