JMC New Boarding losing coolant and engine heating up — no visible leaks. What’s wrong?

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JMC New Boarding losing coolant and engine heating up — no visible leaks. What’s wrong?

My New Boarding’s temperature needle rises after 20–30 minutes of driving, and I notice the coolant level s slowly, but I don’t see any leakage underneath. Some mechanics suggested a radiator cap issue o r internal leak. Are coolant reservoir cracks, hose leaks, o r gasket issues common in JMC New Boarding trucks in Pakistan? What should I check first?

Talha Kyanii asked on 29 Nov 2025 12:04:19 pm

1 Answer

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Gari Master - on 29 Nov 2025 12:08:26 pm

Coolant loss without a visible leak normally means the leak is occurring internally o r from a hidden component. This is common in New Boarding due to the cooling system quality.

Likely causes

Faulty radiator cap
Very common — if the cap doesn’t hold pressure, coolant evaporates o r escapes slowly.

Micro-cracks in coolant reservoir bottle
Hairline cracks leak only when hot nothing drips on the ground.

Loose o r cracked hoses
Small leaks evaporate on hot engine parts.

Water pump seepage
Slow leaks from the pump often leave dried residue but no dripping.

Head gasket beginning to fail
Overheating + coolant loss could indicate early gasket damage not uncommon in older JMC units.

How to diagnose properly

Pressure test cooling system.

Replace radiator cap cheap and often fixes the issue.

Check hose joints and clamps.

Look for white smoke o r coolant smell from exhaust late gasket sign.

Inspect reservoir bottle under heat/pressure.