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2018 S5 3.0T Coolant Loss and Low Coolant Warning

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Chris P. · rep 0 · May 22, 4:25 AM · 1 replies · solved · Question

Vehicle: 2018 Audi S5 Coupe Prestige

Hey everyone,

I'm reaching out because I've been having an issue with my 2018 Audi S5 Coupe Prestige, 3.0T engine. For the past few weeks, I've been getting intermittent 'Low Coolant' warnings on my dash. I've had to top off the coolant reservoir a few times now, and it seems to be losing coolant slowly but steadily.

I've checked under the car and haven't seen any obvious puddles or drips, and there's no sweet smell inside the cabin that would indicate a heater core leak. The car isn't overheating, at least not yet, and there's no white smoke from the exhaust. I'm worried about where this coolant is going.

Has anyone with a B9 S5 or similar 3.0T experienced this? What are the common failure points for coolant leaks on these engines?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:25 AM

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ClearTheCode admin answer:

Coolant loss on the 3.0 TFSI engine, like in your 2018 Audi S5, is a well-documented issue, and it's wise to address it promptly to prevent potential overheating and engine damage. The absence of visible leaks on the ground can make diagnosis tricky, as some leaks are internal or only occur under specific conditions.

Here are the common causes for coolant loss on these engines:

  1. Water Pump Failure: The mechanical water pump on the 3.0 TFSI is a common failure point. It can develop slow leaks that are hard to spot, often dripping onto hot engine components where the coolant evaporates before hitting the ground.
  2. Thermostat Housing/Assembly: The thermostat housing, often integrated with other components, can crack or develop leaks, especially where plastic components are used.
  3. Coolant Hoses and Connections: Over time, rubber hoses can degrade, or clamps can loosen, leading to small, intermittent leaks. Look for crusty pink/white residue around hose connections.
  4. Supercharger Intercooler (Internal Leak): The 3.0 TFSI uses a liquid-to-air intercooler integrated into the supercharger. An internal leak in this component can allow coolant to be drawn into the intake manifold and burned off, resulting in no external signs. This is a more serious issue.
  5. Expansion Tank/Cap: A faulty coolant expansion tank or a failing pressure cap can lead to coolant loss, either through evaporation or by not holding pressure correctly.

When to see a shop: Given the lack of external signs, a professional diagnosis is highly recommended. An Audi specialist will typically perform the following:

  1. Coolant System Pressure Test: This involves pressurizing the cooling system when the engine is cold to simulate operating pressure and help reveal leaks that might not be visible otherwise.
  2. Visual Inspection with UV Dye: Adding UV dye to the coolant and inspecting with a UV light can help pinpoint elusive leaks.
  3. Borescope Inspection: If an internal supercharger intercooler leak is suspected, a borescope can be used to inspect the intake manifold and cylinders for coolant residue.

Do not ignore the low coolant warning, as continued driving with insufficient coolant can lead to engine overheating and severe damage.

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