Expansion tank <em>Nissan Sunny FB15</em>: device, diagnosis and replacement

Nissan Sunny FB15 is a popular sedan that is valued for its reliability and ease of maintenance. However, even such machines eventually have problems with the cooling system, and one of the key parts here is expansion tank. This element not only compensates for changes in the volume of coolant, but also serves as an indicator of the condition of the entire system.

Owners FB15 often encounter cracks in the tank, antifreeze leaks or premature wear. In this article we will look at how recognize a fault, which tank to choose for replacement, and how to carry out the work yourself - taking into account the nuances of this particular model. We will also consider typical mistakes that lead to repeated breakdowns and give recommendations for prevention.

Functions and design of the expansion tank in Nissan Sunny FB15

Expansion tank in Sunny FB15 performs three main tasks:

• 🔹 Antifreeze expansion compensation when heated (the volume of liquid increases by 10–20% at engine operating temperature).
• 🔹 Relieving excess pressure through the valve in the lid (prevents rupture of pipes or radiator).
• 🔹 Visual inspection of coolant level — there are marks on the tank MIN And MAX.

Structurally, the tank FB15 is a plastic tank with two fittings: upper - for connection to the radiator via a steam outlet hose, lower - for circulation of antifreeze from the engine. Built into the lid safety valve, which operates at a pressure of ~1.1–1.3 bar. If the valve gets stuck, the cooling system will begin to “pressure”, which will lead to leaks or overheating.

Feature Sunny FB15 — the tank is installed in upper right corner of the engine compartment, next to the battery. This simplifies access for inspection, but increases the risk of mechanical damage due to careless maintenance. Tank material - polypropylene, resistant to ethylene glycol-based antifreezes, but over time it loses its elasticity due to temperature changes.

Signs of a malfunctioning expansion tank

Problems with the tank manifest themselves in both obvious and indirect symptoms. If you ignore them, the consequences may backfire engine overheating or damage to the radiator. Pay attention to the following signals:

• 🚨 Antifreeze puddles under the car (especially after parking) - often indicates cracks in the bottom of the tank or loose hose clamps.
• 🚨 White smoke from the exhaust pipe - may indicate that antifreeze has entered the cylinders through a burnt-out cylinder head gasket (but check the tank first!).
• 🚨 Frequent operation of the cooling fan — if the tank does not hold pressure, the system operates in emergency mode.
• 🚨 Deformation or swelling of the tank - a sign of a faulty lid valve (pressure is not released).

On Sunny FB15 There is a specific symptom: if, when the engine warms up, you can hear hissing, this means that the valve allows air to flow in the opposite direction. As a result, air pockets form in the system, and the stove blows cold air. You can check this by squeezing the upper radiator hose with your hand - if it is soft, there is no pressure in the system.

⚠️ Attention! If the antifreeze goes away, but there are no signs of leakage, check tank cap condition. Worn valve rubber can leak liquid in the form of vapor through microcracks. B FB15 this often results in a "dry" reservoir while the engine is running.

How to check the expansion tank and cap

Tank diagnostics Nissan Sunny FB15 can be carried out without specialized equipment. Follow this algorithm:

1. External inspection:
   • 🔦 Check the tank for cracks (especially in the places where the fittings are attached).
   • 🔦 Inspect the hoses for softening or cracking - This is a sign of aging rubber.
   • 🔦 Make sure the tank is not deformed (bloating indicates excessive pressure).
2. Checking the cover:
   • 🔧 Remove the lid and shake it - if you hear rattling sound, the valve has become detached from the body.
   • 🔧 Press the valve with your finger: it should spring back and return to the starting position.
3. Leak test:
   • 🚿 Place the lid on the tank and create pressure (for example, blow into a hose). If air escapes through the valve, the cap is faulty.

To accurately diagnose the cap valve, you can use pressure test pump (costs ~1,500 rub.). Connect it to the tank and pump up the pressure to 1.1 bar - the valve should work. If the pressure continues to rise, the valve is stuck. B FB15 this often leads to rupture of radiator pipes, since the system does not relieve excess pressure.

Selecting an expansion tank for replacement

Original tank for Nissan Sunny FB15 has an article number 21410-4M000 (or 21410-4M00A for restyled versions). Its average price is 2,500–3,200 rubles. However, there are high-quality analogues on the market that are cheaper:

Brand	Article	Price, rub.	Features
Nissan (original)	21410-4M000	2 800–3 200	1 year warranty, precise fit
Denso	555-0106	1 900–2 300	Reinforced plastic, compatible with Almera N16
Febi	21410	1 500–1 800	Budget option, may require modification of fittings
Hella	8GF 355 379-121	2 100–2 500	New cap with valve included

When choosing an analogue, pay attention to: material (must be heat-resistant polypropylene), fitting sizes (in FB15 the upper fitting is thinner than the lower one), complete set (some tanks are sold without a lid).

⚠️ Attention! Do not buy tanks without markings or with the inscription “universal”. B Sunny FB15 non-standard arrangement of fasteners, and the “universal” tank may not fit into its standard place.

If you plan to replace only the cover, the original part number is 21430-4M000 (price ~800 rub.). Alternatives: Febi 21430 (600 rub.), Gates TC3001 (900 rub.).

Step-by-step instructions for replacing the tank

Replacing the expansion tank with Nissan Sunny FB15 takes ~1 hour and does not require special tools. You will need: key for 10 (for clamps), flat blade screwdriver, new antifreeze (1–1.5 l for topping up), rags.

Sequence of actions:

1. Drain the antifreeze:
   • 🔧 Unscrew the cap on the radiator (bottom right) and drain the liquid into the container.
   • 🔧 Disconnect the bottom hose of the tank to drain the residue.
2. Remove the old tank:
   • 🔧 Loosen the clamps on both fittings and remove the hoses.
   • 🔧 Unscrew the bolt securing the tank to the body (10 wrench).
3. Install a new tank:
   • 🔧 Transfer the mount from the old tank to the new one.
   • 🔧 Connect the hoses, starting from the bottom (to avoid air locks).
4. Fill with antifreeze:
   • 🔧 Fill the tank to the mark MAX.
   • 🔧 Start the engine and add fluid after warming up (the level will drop).

An important nuance: in FB15 after replacing the tank definitely need to bleed the systemto remove air pockets. To do this: unscrew the radiator cap → start the engine → let it idle for 5 minutes → add antifreeze to the level.

What happens if you don't bleed the system?

Air locks will lead to uneven cooling of the engine. As a result, local overheating is possible (especially in the area of ​​the 4th cylinder), which is fraught with deformation of the cylinder head.

Typical replacement mistakes and how to avoid them

Even experienced car owners make mistakes when working with the expansion tank. Sunny FB15. Here are the most common:

• ❌ Using incompatible antifreeze. B FB15 factory recommended Nissan Coolant L248 (green) or ethylene glycol-based analogues. Mixing with cheap antifreeze leads to corrosion of aluminum parts.
• ❌ Pulling the clamps. The plastic tank fittings can crack if the clamps are tightened too much. Optimal effort - hand tightening + 1/4 turn wrench.
• ❌ Ignoring air jams. If you do not bleed the system, the heater will blow cold air and the engine will overheat.
• ❌ Installing a tank without flushing the system. Remains of old antifreeze with sediment will clog the new tank and radiator.

Another mistake - buying a tank without a lid. B FB15 the cap valve is designed for a specific pressure, and a “universal” cap may not work at a critical moment. For example, if the valve opens at 0.9 bar instead of 1.1, the system will “pressure” and the hoses will quickly fail.

Prevention and increasing the service life of the tank

Average life of the expansion tank in Nissan Sunny FB15 — 5–7 years or 100,000 km. However, with proper maintenance this period can be extended:

• 🛠️ Monitor the antifreeze level once every 2–3 months. Level drop below MIN accelerates seal wear.
• 🛠️ Change antifreeze every 5 years (or 90,000 km). Old fluid loses its lubricating properties, and the plastic of the reservoir becomes brittle.
• 🛠️ Check the reservoir cap at every maintenance. The valve should open freely when pressed.
• 🛠️ Avoid mechanical stress on the reservoir (for example, when washing the engine compartment under high pressure).

In winter, it is especially important to monitor antifreeze concentration. B FB15 The optimal ratio of water and concentrate is 50/50. If the liquid is too diluted, it freezes at −15°C, resulting in microcracks in the tank. You can check the concentration with a hydrometer (costs ~300 rubles).

It is also recommended once a year flush the cooling system special compounds (for example, Liqui Moly Kuhler-Reiniger). This removes deposits that clog the tank fittings and reduce its efficiency.

Frequently asked questions (FAQ)

Is it possible to drive with a cracked reservoir if you add antifreeze?

No, it's dangerous. The crack will increase over time, and at one point the tank may burst, leaving you without antifreeze. In addition, air enters the system through the crack, which leads to overheating of the engine. Replacing the tank will cost less than repairing the cylinder head after overheating.

What antifreeze should I fill in Nissan Sunny FB15?

Recommended by the factory Nissan Coolant L248 (green, ethylene glycol based). Alternatives: Coolstream A-110, Sintec Unlimited G12+. The main thing is not to mix different types (for example, G11 and G12) and not to use TOSOL. The volume of the cooling system is 6.7 liters, but when replacing the tank it is enough to add 1–1.5 liters.

Why does the stove blow cold air after replacing the tank?

This is a sign air lock in the system. To fix it:

1. Start the engine and let it warm up to operating temperature.
2. Unscrew the radiator cap and add antifreeze to the edge of the neck.
3. Squeeze the upper radiator hose with your hand several times to help expel the air.

If it doesn't help, check thermostat — it could get stuck in the open position.

What is the difference between the tank for FB15 before and after restyling?

In restyled versions (since 2014), the tank has an article number 21410-4M00A and a slightly modified shape of the upper fitting. However, both options are interchangeable - the only difference is in the fastening of the steam hose. If you buy an analogue, check with the seller for compatibility with your year of manufacture.

Is it possible to repair a cracked tank?

Theoretically, you can seal the crack epoxy glue or cold welding, but this is a temporary solution. The plastic of the tank is constantly exposed to temperature stress, and the patch will soon fall off. In addition, the repaired tank may not withstand the pressure and burst. We recommend replacing it with a new one immediately.