Inquiry about the cooling system

[mixturegro]

I just serviced the cooling system of my 1991 Range Rover Classic by flushing the radiator, replacing many hoses, and installing a new thermostat, fan, and viscous coupling. I successfully bled the system (maintaining steady temperatures and optimal heater function) and let it to idle for around thirty minutes with the expansion tank cover off. After reattaching it and taking it for a test drive, it rapidly overheated, prompting me to turn it off and open the hood. Coolant was ejected from the expansion tank top.

It is my conjecture that, given its proper functioning with the cap off, the system is preventing pressure from being released in the expansion tank. Additionally, I conducted a head gasket block test, which yielded a positive result; thus, I infer that the issue lies elsewhere. During my investigation on components, I saw two fundamental cap designs: one using an integrated coolant level sensor (similar to mine) and another that is only a standard cap. Do they both function identically on RRCs? At a certain pressure, do they permit the discharge of that pressure? Should I get a new coolant level sensor cap?

All counsel is appreciated!

[stormwavy]

Is it possible that air is trapped?

[1apissugar]

Is the radiator authentic? What is its age? A flush may be insufficient at this age. It may be necessary to replace the radiator or, at a minimum, have it rodded or re-cored.

[mixturegro]

Thank you for the replies. I cannot entirely exclude the possibility of trapped air or a deteriorated radiator; nonetheless, I would appreciate assistance in comprehending the operational mechanics of the cooling system. More specifically, how does the presence of the expansion tank cap influence any aspect? Assuming the head gasket is intact, what other factors may contribute to elevated pressure? Alternatively, the system pressure may be enough, and my cap may not be releasing pressure as intended.

A plugged heater core might also be a problem. I observed that the top and lower vents emit hot air, however the middle fascia vents release just warm air. Could that induce excessive pressure inside the system?

[veinedpanty]

Your reaction suggests the potential for trapped air inside the system. Numerous methods and techniques exist to alleviate air, with the most effective being the use of a lift pump. Compressed air is used to generate a vacuum inside the system and facilitate vacuum filling.

[veinedpanty]

https://www.cpsproducts.com/product-details/550500/

 

I strongly endorse it; it alleviates much frustration.

[ultimatesoy]

I had several cooling issues similar to yours with my old vehicle. Upon doing all the necessary actions, I discovered that the issue was a defective thermostat. Purchase a distinct replacement; install it properly and do further testing. I invested substantial resources pursuing more intricate challenges. Verify the simplicity twice!

Best of luck
1990 has passed; 1995 LWB remains unparalleled.

[mixturegro]

I had the same sentiment about the thermostat, hence I changed it when the radiator was being serviced. No solution for the straightforward remedy there.

I want to attempt to bleed once again. It is hoped that the issue is only air trapped in the system. I lack an air compressor or connection; thus, I am unable to use that vacuum fill tool.

Is there a distinct heat source for the higher and lower vents compared to the middle vents? It is peculiar that one becomes very hot while the other remains only warm.