LPG/GBO installation — cooling-system effects

Tags: #overheating · #thermostat · #water-pump

Multiple owners who installed an LPG/GBO gas-conversion system reported cooling-related overheating symptoms afterward. Two independent case threads are combined here because they converge on the same diagnostic logic.

Case 1 — 115,000 km, 2017 X80, post-GBO overheating. After installing LPG on a 2017 car with 115k km, the owner saw a check-engine light and coolant temperature of 99–102°C both at highway speed and idle — abnormal for those conditions.¹² An initial antifreeze top-up (coolant had been low, topped to max) did not resolve it.³ Diagnosis narrowed to a combination of: (1) an air pocket introduced in the cooling system during GBO installation and component relocation (the GBO reducer is commonly mounted above the original coolant hose routing, which the installer's own forums flag as an air-trap risk);⁴ (2) possible thermostat malfunction — a cold lower hose indicates the large cooling circuit isn't opening;⁵⁶ or (3) radiator blockage/cleanliness. The gas installer in this case struggled at length to get the thermostat to circulate both loops properly.⁷ Community consensus in this thread: thermostat failure and air pockets are the primary suspects — GBO itself does not directly cause overheating by design, but poorly installed or poorly maintained GBO plumbing can.⁸

Case 2 — general post-LPO overheating pattern. A second, broader thread on post-LPG-installation overheating narrowed the cause list to: (1) air pockets in the heater-radiator circuit from incorrect hose routing during install; (2) incorrectly positioned LPO hoses; (3) a defective thermostat; or (4) a failing water pump.⁹ Diagnostic test: rev the engine on gas and check whether the lower radiator hose heats up — if cold/barely warm, the thermostat is likely at fault; if it heats normally, the water pump is functioning.¹⁰¹¹ Also check the radiator cap — a cap that doesn't hold pressure was flagged as a contributing factor in at least one case, and cap replacement was recommended alongside the other checks.¹² Multiple owners in this thread reported the same symptom pattern resolved specifically by thermostat replacement.¹³ There was live debate on which component to test first (pump vs. thermostat); the resolution reached was that a cold/barely-warm lower hose while revving on gas points to thermostat first, since a failing pump would still let some warmth through via circulation, whereas a stuck-closed thermostat blocks the large loop outright.¹⁴

Air-pocket formation after component relocation. When a GBO reducer or other add-on component is mounted above the original coolant hose routing (a common LPG-install pattern), air pockets can form in the system and prevent proper flow through the large cooling circuit. Purge methods reported: gentle acceleration with the front of the car raised, or repeating several heat cycles (drive/cool/drive) to work the air out gradually.⁴¹⁵

Thermostat/fan behavior runs 4–5°C higher on gas than on petrol. A separate report describes the baseline thermostat operating pattern by fuel type: on petrol, the thermostat opens at 99°C, initially dips to 93°C, then stabilizes around 84°C in normal operation. On gas (LPG), the same pattern repeats but shifted 4–5°C higher throughout, with the cooling fan typically engaging at 99°C and disengaging at 95°C — attributed to gas burning at a higher combustion temperature than petrol. Separately noted as a contributing design factor: the X80's thermostat sits in an unusual location (not at the end of the cylinder block, where temperature is normally highest), which is described as a general contributor to the model's cooling challenges regardless of fuel type.¹⁶¹⁷¹⁸

Media

Engine bay photo showing the LPG/GBO reducer installation, illustrating its position relative to the radiator cap and coolant hose routing discussed in the diagnosis

Related pages

• Thermostat failure — symptoms and diagnosis
• Thermostat replacement and cooling-system bleeding
• Coolant overheating — a long diagnostic case
• Serpentine belt failure and coolant loss
• Thermostat — parts and replacement

Sources

This page is compiled from 18 community messages. Every fact carries a numbered reference to its original author and message.

Last updated: 2026-07-24