Is the honeymoon over (new XJ)?

[tazwegion]

Well it's towed mammoth enclosed furniture trailers without incident and never (according to the temperature gauge) gone far above 1/2 during my ownership (dual thermos cut in at 105c) but odd coolant leakage has been noted this week...

• periodic excessive overflow when vehicle turned off (day-to-day commuting)
• bubbles large and small in radiator
• will force all of the coolant out of the radiator if cap left off
• drives fine and loses virtually no coolant when kept under normal operating temp
• there is NO oil in the water
• there is NO water in the oil
• there is NO noticeable white (water) byproduct from the exhaust

Previous owner claimed to have (prior to sale)

• Replaced cylinder head
• water pump
• thermostat
• radiator
• replaced fan (with electric)
• coolant hoses

I'm thinking it's one of three possibilities but I thought I'd run it past the forum guru's for additional feedback

• blown head gasket (not installed and/or torqued correctly)
• cracked cylinder head
• cracked cylinder wall (block)

I'm wondering if a coolant system pressure test would indicate whether or not the coolant is being additionally pressurized by leaking compression OR would a cylinder compression test provide a better indication? I'm hoping for a bad head gasket (fingers crossed)


Any thoughts? suggestions? advice? alternative testing regimes?

[Deezelweazel]

Hm... thermostat build in upside down?
There is a small vent hole in it. which must be upside to enable venting of air bubbles.
If it is build in wrong- it fits on your description.

[tazwegion]

Originally Posted by Deezelweazel

Hm... thermostat build in upside down?
There is a small vent hole in it. which must be upside to enable venting of air bubbles.
If it is build in wrong- it fits on your description.

Really? I hadn't heard that one before but an easier fix than a new head gasket and/or block/head repair (or replacement)... thanks, do you think you could go into anymore detail as to why that would cause such symptoms?

[Deezelweazel]

easy, there is a small movable ball (2mm?) built in the thermostat housing, acting as a valve, which allows air bubbles to escape from the radiator circuit into the expansion chamber. If the thermostat is built in upside down, they can't escape and are accumulated in the radiator (air is floating on top). Causing the trouble you have.

[tazwegion]

Originally Posted by Deezelweazel

easy, there is a small movable ball (2mm?) built in the thermostat housing, acting as a valve, which allows air bubbles to escape from the radiator circuit into the expansion chamber. If the thermostat is built in upside down, they can't escape and are accumulated in the radiator (air is floating on top). Causing the trouble you have.

Ah thanks for the explanation...


So essentially because the air is trapped under the thermostat, when it finally opens it's under such pressure that it rushes out of the cooling system instead of slowly until completely bled (air pocket free)?

[Deezelweazel]

Exactly.
To increase that problem- the thermostat does operates not correctly, because of the entrapped insulating air