My CX5 2.2 diesel's engine has been refurbished by a reputable UK Engine company with the head pressure tested, head gasket replaced along with a new water pump. The radiator was replaced but not the radiator cap.
After 680 miles it is overheating and spraying coolant over the front of the engine cover.
I let it cool overnight and I am then able to top up the radiator with a significant amount of coolant. The cycle then starts once more.
If, from cold, I top up the coolant, leave the radiator cap off and then start the engine, coolant shoots upwards.
With the radiator cap in place and the engine warm and running I cannot see any coolant escaping however when the engine revs are increased the overflow bottle fills and it's top becomes detached spraying coolant over the engine.
​​​​​There is no liquid showing under the vehicle, the exhaust is not showing steam or vapour escaping, fuel economy is excellent and the engine runs smoothly UNTIL it overheats.

All advice, guidance and suggestions will be appreciated, thanks

 

You should check for the following issues:
1. VERIFY PCM DTC.
2. VERIFY CURRENT INPUT SIGNAL STATUS.
3. INSPECT A/C RELAY.
4. INSPECT FAN CONTROL MODULE NO.1, NO.2.
5. INSPECT COOLING FAN MOTOR NO.1, NO.2.
6. DETERMINE IF MALFUNCTION CAUSE IS THERMOSTAT OR OTHER.
7. INSPECT THERMOSTAT.
8. INSPECT SEALING OF ENGINE.
You can refer other mazda repair manuals on the website: mazda cx5 2014 repair manuals.

 

Sounds like Cylinder Head Gasket as the Water Collant System is getting overpressurised and that normally occurrs from a leaky head/head gasket??

 

Thank you, my thought too but nice to have it confirmed

 

Yes unfortunately in my experience Head Gasket leaks at the start, especially on Diesels, squirt a tiny amount of gas into the coolant system on cylinder firing - but that squirt is under the immense pressure of combustion.

The water cannot squirt back as the coolant pressure is many magnitudes lower, and so in the early days, the leak acts like a one way valve.

After time and erosion, the leak gets progressively worse until you get to the point of seeing bubbles in the header tank and actually water can squirt in the oppose direction leading to coolant loss. You may also see some dark staining in the header tank.

A specialist sensitive gas probe can be used in the header tank and this can detect combustion gases and therefore the early stage failure.

I don’t subscribe to the thermostat being the root cause - that failure can only generate pressure from it being jammed closed and causing overheating > coolant boiling which should be detected by the engine temperature sensor.

There may be other failure modes on these engines and I have no specific experience, so my comments are based on many years of general automotive engineering.

Best of luck Swampdonk3y in your endeavours to seek and repair.