Cooling System Maintenance

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The only regular maintenance items called for by the Workshop Manual are:

 Daily (!):                            Check the water level in the radiator

Every 12,000 miles:           Drain the system, replace the coolant and lubricate the water pump.

 This tends to understate the attention that the system will require on a car that is 50 years old or more, though, often, the need to drain the system to perform other maintenance operations means that this work is carried out to a schedule imposed by other circumstances.

It is normally accepted practice now to regard anti-freeze more as a coolant conditioner that can usefully remain in the engine all year round, assisting with prevention of engine corrosion and helping with pump lubrication. No false economies here: use a good brand. It is generally a good idea to top up with anti-freeze solution rather than plain water, to avoid dilution over time, so carry a container with a made-up solution in the boot.

Over-heating and problems in the cooling system generally arise from:


  • 1. Leakage. This can be because of loose hose clips, damaged hoses, damaged radiator, failure of thermostat housing gasket and worn pump.
  • 2. Blockage. Over time, sludge builds up in the radiator and the engine block, narrowing the water passages. Hoses can also collapse internally with age, restricting flow. The thermostat may also fail, preventing heated water from reaching the radiator.
  • 3. Wear in the pump. This will eventually lead to catastrophic failure of the bearings.
  • 4.Inadequate flow caused by a loose fan belt.

 Leaks will generally come to your attention because the system needs topping up too often or you see water or steam escaping from the problem area. They are generally easy to deal with. Tightening of the joint or replacement of the relevant part is normally all that is required. If that part is a radiator damaged by a front impact or a flying stone, then a specialist will need to insert a new core by unsoldering the top and bottom tanks and fitting them to a new core section. If you are having this work carried out, it is worth considering the extra expense of a high-efficiency core, especially if your car was prone to overheating on long fast runs or in hot weather. Minor leaks from the radiator can be overcome with an additive that congeals at the leak site when it contacts the air. This is fine as a roadside “get-you-home” fix and it is worth carrying Bars Leaks or something similar for the purpose but it is only a temporary solution. Getting the radiator repaired is the only long-term answer. Small holes can often be soldered up without the need for recoring. And I’ve never really fancied the old tip of breaking an egg into the radiator. Let’s keep egg poaching in the kitchen!

If the leak is coming from around the fan spindle on the water pump, then it indicates that the internal seal has failed and water is getting on the bearings. They will fail as a result, so either fit a new pump before it lets you down or, if you have one of the older type and want to retain the originality, rebuild it with new seals and bearings. Only very early pumps had provision for lubrication and many have been replaced now with the “sealed-for-life” type.

 Loss of coolant can be caused by two problems not associated with simple leakage: 

  • a) A worn or incorrectly rated radiator cap. A cap spring that is too weak will allow hot water to escape via the overflow at normal working temperature rather than at elevated temperatures as intended.
  • b) A leaking cylinder-head gasket. This allows compression from the engine to escape into the water-jacket. This artificially raises the water pressure and forces water out past the radiator cap by-pass. A clue to this is air bubbles seen rising in the radiator and a white “emulsion” on the underside of the oil filler cap, indicating that the ineffective gasket seal is also allowing steam into the oil ways. Do a compression check and if this confirms a problem, replace the gasket before you have a more serious failure to deal with.

Replacing hoses regularly is a relatively inexpensive part of preventative maintenance. As soon as you see any external cracking on a hose, especially around the jubilee clip, replace it. And if a hose feels weak and can be easily collapsed with a squeeze it is probably time to change it. A new range of silicon hoses has recently become available for classic cars. Unlike their modern counter-parts, they are not in garish colours but plain black, so they sit unobtrusively in the engine bay whilst offering resilience and life-span far superior to the old rubber-on-canvas hoses. 

To avoid the slow deterioration caused by sludge build up, it is a good idea to flush the system every few years. This involves draining the system and forcing clean water through it in the reverse direction to its normal flow, so as to dislodge sludge hiding behind internal parts. In broad terms, “reverse” means up the radiator and down the engine. Proprietary additives can be used to assist in dissolving sludge before flushing. Push the water through until it is flowing clean from the output end. If you have the radiator out for other reasons, always give it a good flush while you have the chance.  If you rebuild the engine it is worth the expense of “hot-tanking”, which involves using a chemical to clean all accumulated sludge and rust out of the block. And don’t forget the heater. Sludge is a major cause of poor heating performance and because the heater matrix is not drained with the rest of the system, it is important to flush out the sludge regularly. The best way to flush is to make up a joint that will allow you to connect a garden hose securely onto one of the radiator or heater hoses. Then you devise a way of carrying the waste water away from the open connection at the other end. Some old lengths of copper or plastic domestic water pipe and some jubilee clips will normally do the job. 

When flushing, take the opportunity to service the drain taps. They are often corroded stiff or blocked with sludge, (one on the base of the radiator and one on the right-hand rear of the engine, near the distributor). The one on the engine block is necessarily at the lowest point in the water-jacket but this also means that it is a primary collection point for sediment that sets into a hard sludge. If you unscrew the tap and no water comes out, it shows that the small waterway that it connects to is already blocked. This means that you can’t properly drain the coolant from this point and the sludge will stay put. Clear it out by poking hard with a piece of bent wire until water flows freely and clean. Dismantle the taps and lubricate them before refitting 

A loose fan belt is often revealed by a loud screaming noise as you accelerate away after starting up. This is because it takes the loose belt a while to get a grip on the fast spinning pulley and the resulting friction makes the noise. It also causes poor charging at the dynamo. However, don’t leave it to that stage before you spot it. That’s for amateurs. It’s easy enough to give the belt a quick check when you have the bonnet up. But conversely, don’t be tempted to over-tighten the belt. This will cause rapid pump and dynamo bearing failure. The correct adjustment gives 1” (2.5mm) free movement at the centre of the longest belt run. Adjustment is achieved by slackening the dynamo mounting bolts and the clamp nut on the front of the engine below the water pump. This is another “three-hand” job beloved of car designers, because, for holding the dynamo in the right position whilst tightening the clamp nut, two hands are barely adequate. 

Travelling from Surrey to central Italy I once consumed five fan belts, which would get progressively slacker and slacker, then break. I was completely stumped as to the cause until I had the chance to take a proper look when we reached our destination. I had recently replaced the standard engine with a 1622cc unit. The swap had been straight-forward and I had cleaned and re-painted the belt pulleys before re-fitting them. What I hadn’t noticed was that the deep groove on the crankshaft pulley had acquired some significant internal corrosion during lay-up. This was acting as a very effective abrasive and over continental mileage was grinding the belts down to nothing! I administered a quick buff-up of the groove with emery cloth and the problem disappeared. 

If you have serious over-heating problems, see the separate article on the subject.