Engine and cooling NA
The NA engine is tough, reliable and much more willing than the figures would suggest. It is not uncommon for them to reach 200k without needing a major rebuild. Be very wary of cars that claim to have less than 100k on them; the cars wear their miles very well.
Despite the rumours, very little is shared with any VW so some sourcing parts can be tricky.
The K-Jet system is a carefully balanced one and a fault in any part of it can cause poor running. Starting from cold should be quite swift and it should settle into a fast idle around 1200-1500rpm. As the engine warms this will gradually fall to a warm idle around 900-1000rpm. Fluttering idles are usually air leaks or issues with leads or plugs. Reluctance to start or run without throttle are often faulty warm up regulators, fuel metering heads or cold start valves.
Warm starting is the 924s most common problem. Fuel pumps and regulators are often at fault for these. As the parts are quite expensive, lots of historical bodges and mysterious cabin switches were common to work around them. Few, if any, of them are successful.
A well set up K-jet system should be reliable and stay in tune easily. Too many people unfamiliar with the system mask problems by tweaking mixtures randomly, causing problems further down the line.
Check the oil filler cap for mayonnaise. Any sign of this might indicate a head gasket on the way out. While there check that the cam lobes show signs of oil being delivered to them. The plastic elbow in the spray bar can fail, starving them of oil.
Check the expansion tank is at the right level and has the correct mix of antifreeze. It must have antifreeze at 50:50 mix. The iron block and alloy head will block up if not.
Radiators, despite their low position are quite dependable especially if the undertray and radiator grill are present. Surprisingly the 924 engine holds temperature well, even though the grill opening is tiny. Radiators can be recored for a reasonable price.
Failures in the expansion tank are often due to age and heat cycles. They last ages but when they go it is around the seams. They are available new again.
Check the heater matrix valve above the clutch housing. It’s operated by a cable to the cabin controls. Check it moves! Leaks here can contaminate the clutch.
Oil leaks are an inevitable part of old car ownership. The 924 is not particularly prone to them but there are places to check. The alloy sump plug is tapered and if overtightened or not fitted with a new copper washer can weep. The sump gasket can break down and seep. The front crank seal is integral to the oil pump and a mail oil channel sits near it. If either the pump seal or the crank seal fail oil will pour from this area. Oil leaks can often be disguised as there is an engine undertray fitted, check very carefully for evidence that it is oil tight.
Oil can seep from the rocker cover. The gasket is a cork one with silicon end pieces. It’s an easy job to repair and needs to be removed as part of the tappet inspection and adjustment. If it is weeping, it is an easy fix.
The bottom end on an NA is massively over engineered. As such, unless it has been massively abused, there should be no problems here.
The pistons have an unusual arrangement with no oil scraper rings. Consequently, some smoke can often be present on initial start up as oil is burnt. This should immediately disappear.
The timing belt is possibly the easiest on any overhead cam engine. It will take you longer to remove the timing belt cover than fit a new one. Our club record is 7 minutes and 23 seconds! It is also a non-interference engine so, in the unlikely event that the belt did snap, no damage will be done.
Oil pressure from cold should be 5-6 bar at idle. Once warm this should drop to 2-3 bar.
On a test drive check for vibrations at idle that disappears at 1200rpm. This indicates one or both engine mounts have failed. They are currently not available new.
Engine servicing on an NA is dirt cheap. Belts, oil, plugs and filters will cost less than £50 and they’re all easy.
