D1-30 expansion tank cap leaking

[jlavery]

We've got an annoying small but persistent leak from the expansion tank cap on our D1-30, when the engine is up to temperature.

Any suggestions as to a fix, short of replacing cap/tank. I've checked and carefully cleaned the tank rim and cap seal.

 

[VicS]

We've got an annoying small but persistent leak from the expansion tank cap on our D1-30, when the engine is up to temperature.

Any suggestions as to a fix, short of replacing cap/tank. I've checked and carefully cleaned the tank rim and cap seal.

Be sure not to overfill the system. Try leaving the coolant level slightly lower than normal rather than making good any loss
You are sure the engine is not over heating slightly?
Other things could cause the system to over pressurise ..... see this thread Volvo Penta MD2020 dumped all coolant in bilge under engine

If you do simply need a new cap this one is probably the correct one and a lot cheaper than a genuine part Expansion Tank Cap, Most Models 1977-2008 (see info)

 

[jlavery]

That thread is really useful, thanks.

Thoughts:

• Don't think overheating. IR thermometer showing about 70c around block.
• Massively good flow out of exhaust, so think blocked elbow unlikely. I'll check the elbow hose.
• HE core looked good last year when I was checking previous overheating problem (was air in fresh system, and didn't result in coolant leak).
• Could be calorifier I suppose. But this is a small leak rather than a 'dump'. Luckily I can turn off feed to calorifier (it's a bypass on the D1-30), so could try shutting it off.

 

[jlavery]

Replacement tank cap and not overfilling seems to have cured it.