Parts for your 1991 Mitsubishi Pajero-Heater core

1991 Mitsubishi Pajero Heater Core — What It Does and How to Look After It

Technical references confirm the 1991 Mitsubishi Pajero is factory-fitted with a heater core (often called a heater radiator). This is documented in the Mitsubishi Pajero/Montero Workshop Manual, Group 55A Heating & Air Conditioning, listed in the Mitsubishi ASA/CAPS parts catalogue for 1991 model-year HVAC components (heater radiator, tap, and hoses), and covered in aftermarket manuals such as Haynes and Max Ellery for early Pajero/Montero models.

On a 1991 Pajero, the heater core is a compact radiator tucked inside the heater/AC box under the dash. Engine coolant flows through it, and the blower pushes air across the fins to warm the cabin and demist the windscreen. When it’s healthy, it’s set-and-forget comfort, when it’s tired, it can cause foggy glass, a sweet coolant odour, damp carpets and annoying coolant loss.

Good servicing keeps the core happy. Regular cooling system maintenance matters more than most people think: refresh the coolant at the recommended intervals, use the correct ethylene glycol type for Mitsubishi of the era, and avoid mixing brands or colours. During coolant changes, run the heater on full hot and properly bleed air from the system—air pockets can reduce heater output and stress the core. Check heater hoses, clamps and the heater tap for perishing or seepage, especially where hoses pass through the firewall. Many 1991 Pajeros don’t have a cabin/pollen filter, so dust can settle on the HVAC fins, when you’re in behind the glovebox for other work, a careful vacuum and light brush-down around the case exterior can help overall airflow.

Replacement is a fair job—typically dash-lift or partial dash removal depending on variant—and can run 4–8 hours for a DIYer with patience. If the core is leaking or badly clogged, it’s best to fit a quality new or re-cored unit rather than gamble on a used one. While you’re there, it’s smart to replace the heater tap, foam seals, O-rings and any brittle vacuum lines or control cables. Label connectors and take photos as you go to make reassembly painless. After refit, pressure-test the cooling system, bleed it with the heater on hot, and recheck coolant level over the next few drives. Get it right once, and the Pajero’s heater will pull its weight on frosty mornings and keep the windscreen clear on wet days.

• Watch for symptoms: sweet smell, foggy windscreen, damp passenger footwell, poor heater output, unexplained coolant loss.
• Service tips: correct coolant, regular flush, proper bleeding with heater on hot, inspect hoses and clamps.
• When replacing: plan time, label everything, renew related seals/hoses, and pressure-test after.

Popular questions about 1991 Mitsubishi Pajero heater cores

How can someone tell if the heater core is failing on a 1991 Pajero?
Typical give-aways are a sweet, syrupy smell inside, misty windows that clear when the heater is off, damp carpet on the passenger side and steady coolant loss without visible engine bay leaks. Tepid heat even with a hot engine can also mean the core is partially blocked. A cooling system pressure test and a quick feel of the heater hoses (both should be hot when the heater is on) help confirm it.

Can the heater core be bypassed temporarily?
Yes, in a pinch the two heater hoses in the engine bay can be looped to bypass the core and stop a leak, letting the vehicle get home or to a workshop. You’ll lose cabin heat and demist performance, so it’s a short-term fix only—sort the core properly as soon as practical.

How long does replacement take, and what else should be changed?
Expect around half a day for an experienced tech, longer for DIY. It’s wise to replace the heater tap, ageing hoses, O-rings and any crumbly foam seals while the dash is apart. Fresh coolant and a thorough bleed with the heater on hot round out the job.