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You'll notice the temp gauge creeping up, puddles of coolant under the car, or the heater not working properly. The engine may consume coolant without obvious external leaks.

The cooling system on these PRV V6 engines is complex, with multiple hoses, a heater valve, and aging seals. Radiators corrode internally after 40 years, heater cores develop pinhole leaks, and hose connections weep. The thermostat housing can crack. Water pumps fail. Head gasket failure is possible but less common if compression is still good.

Start with a pressure test of the cooling system to find leaks. Replace all coolant hoses as a matter of course if they haven't been done, they're cheap insurance. Fit a new thermostat and check the radiator for blockages or leaks. If the heater core is leaking (you'll smell coolant in the cabin), replacement is a dashboard-out job. Water pump replacement is straightforward. Use genuine Volvo coolant and bleed the system properly, air pockets will cause overheating.

The V6 is reluctant to start when cold, runs rough for a few minutes, or won't start at all. Once warm it's usually better.

The Bosch K-Jetronic continuous injection system relies on vacuum-operated components, precise fuel pressure, and a functioning cold start system. The cold start injector (a sixth injector) often fails, the thermo-time switch stops working, and the warm-up regulator sticks. Vacuum leaks are endemic on old engines.

Check fuel pressure at the distributor, should be around 72-77 psi with the engine running, dropping to about 50 psi when the engine is off. Test the cold start injector by removing it and checking for spray during cranking (it should spray for a few seconds then stop). Replace the thermo-time switch if faulty. Hunt down vacuum leaks with a smoke machine or by spraying carb cleaner around suspect areas. The K-Jetronic system can be fiddly; if you're not confident, find someone who knows these systems.

Oil spots on the driveway, oily residue on the underside of the engine, falling oil level.

Every seal and gasket is four decades old. The PRV V6 is notorious for leaking from the camshaft seals, valve cover gaskets, front and rear crankshaft seals, and oil pan gasket. The cam covers are alloy and can warp slightly, making leaks worse.

Systematically replace all gaskets and seals. Cam cover gaskets are easy. Camshaft seals require timing cover removal. The rear main seal is an engine-out or gearbox-out job, so do it if you're already in there. Use quality gaskets, cheap ones won't last. Clean all mating surfaces thoroughly before reassembly.

Uneven idle, hesitation under acceleration, flat spots, check engine light (if fitted).

Ignition system faults are common. The Bosch EZ-series electronic ignition uses a distributor with a Hall effect sensor, ignition coil, and power stage module. The power stage (mounted on the inner wing) can fail. Spark plug leads perish. The distributor cap and rotor wear. The MAF sensor (on later fuel-injected models) can fail or get contaminated.

Start with the basics, new spark plugs (use OEM spec), leads, cap, and rotor. Check the power stage with a multimeter (there are test procedures in the workshop manual). Inspect the distributor for wear or cracks. If fitted with an MAF sensor, clean it or replace if faulty. Check fuel pressure and injector spray pattern. Compression test to rule out mechanical issues.

Overheating, poor heater output, coolant looks rusty or sludgy.

Original radiators are 40+ years old. Internal corrosion blocks coolant passages. Mixing coolant types or using water creates sludge. Electrolysis from poor earthing accelerates corrosion.

Replace the radiator with a new or reconditioned unit. Flush the entire system thoroughly before fitting the new rad. Use the correct Volvo coolant mix (ethylene glycol-based) and distilled water. Check all earth straps, poor earthing can cause coolant to become conductive and corrode alloy components.