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
The coolant thermostat plays several vital roles in a vehicle. So, if it's faulty, it should be replaced ASAP. Often, sealing pastes are used during this process. But, to be blunt, if you're using these pastes during installation, something's off. At least for the "repaired" car, because leaks, failures, and other subsequent damages are just waiting to happen.
So, why shouldn't sealants be used on thermostats?
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.
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.
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.
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".