I brought a new coolant expansion tank and cap for my defender back in January. Fitted no problem. It’s taken to now to get it back on the road due to work etc. Took it out and I started to over heat as I turn back into my street. When I checked there was little to no coolant in the tank and steaming like mad. I checked the tank and the cap was loose and didn’t fit at all. I’ve contacted the supplier who’ve excepted it’s faulty and will replace both but they’ve said a loose cap wouldn’t course the motor to overheat. I’ve done a test today and it’s looking like the head gaskets gone. Am I right in saying a loose cap can course it overheat and I return course head gasket failure.

Sorry for the long post but it’s one thing after another latley.

Maybe you had an air lock when replacing the coolant?

Don’t think I did as I bled the complete system

Questions
Which engine?
What test have you done?
How far did you drive?
Did you check your temperature Gauge?

@Tim Sharp , when filling it's ever-so easy to induce air traps within the coolant system. The air pockets will cause localised hot spots and high pressure points within the cooling galleries, but...this would not normally cause a head gasket to blow unless driven a fair distance.

Tests aside, suggest you drain the coolant and do the following before going down the head gasket route. This to ensure it's not just trapped coolant air pockets.

1. Measure our correct coolant volume i.e. 6 or 11ltrs
2. Remove both radiator and expansion caps
3. Open heater matrix to Hot
4. Slowly, pour coolant in via radiator top - use a watering can or 2ltr plastic lemonade bottle to control rate of pour.
5. Fill til all the pre-measured coolant is in.
6. Alternately squeeze top and bottom hoses to ease out any potential trapped air.
7. With both radiator and expansion caps off start engine and run til temp starts in engine - this is normally enough for the engine to remove trapped air.
8. If not, fit radiator cap but leave expansion cap off - take tratter out for a gentle test run until engine warm. Stop engine, fit expansion cap and drive home.
9. Check coolant levels after an hour or so, topping up if needed.

eta - the reason why it's so important to pre-measure the coolant volume before filling is that if not all the coolant will pour you immediately know you've trapped air somewhere. This trapped air needs to be bled out before continuing to fill.

Don't forget they only pressurise cooling system so it can go over 100°C when working to the extremes of temperature.
So unless you have driven hundreds of miles with a loaded trailer I cannot see a leaking coolant cap causing your issues.

Ive had a similar issue recently. My 90 started overheating on half hr plus drives. I didn't loose much coolant though.

You are right, it could cause a head gasket issue but as lynall said. This is unlikely. The temperature gauge should have picked up the overheating issue before you lost your coolant. (unless its a TDCI. They are a different story!)


Do you have any coolant leaks at all? As it could look like a head gasket, with a vacuum pressure tester, but you have a major coolant leak from another area. On a TD5, I have seen it most commonly out of the coolant temperature gauge housing.

Does it smoke or struggle to start?

Why was it that you changed the first expansion tank cap?


What I would check for first -

1 - Coolant leaks or any form of crystalised coolant (Indicating a persistant leak).

2 - Make sure that you check the thermostat is opening and closing properly. As this can cause excess pressure and overheating. Potentially it could have boiled over. I have replaced a few on both TD5s and one on my TDCI.
I believe you can test it by removing it and put it in boiling water to see if the valve opens. (At that point they are cheap enough you may as well replace it.

3 - I would check the radiator as well. After my TDCI thermostat failed it built up pressure and warped the radiator. Causing it to continue overheating.

lynall said:

Don't forget they only pressurise cooling system so it can go over 100°C when working to the extremes of temperature.
So unless you have driven hundreds of miles with a loaded trailer I cannot see a leaking coolant cap causing your issues.

Click to expand...

While this is absolutely true there are many hot areas that the coolant passes through where for a moment it will be at above boiling point till it mixes with "colder" water or metal

that cap is very NB

D1Nut said:

While this is absolutely true there are many hot areas that the coolant passes through where for a moment it will be at above boiling point till it mixes with "colder" water or metal

that cap is very NB

Click to expand...

I see lots of dead caps at work on trucks, and whilst they do spit out some coolant they do not overheat, which is amazing sometimes as the bloody drivers do not check their levels, it is only when the low coolant alarm comes on that they visit the workshop!