By Kev Rooney
Nothing is more worrying in your rod or kustom than the constant fear of overheating. Whether you’ve just put it on the road, bought a completed car or just installed a new rad, all can be fine tuned or tweaked. So starting at the very beginning is your vehicle ACTUALLY overheating? By this I mean physically throwing water out rather than a worrying gauge reading. If it reads hot but isn’t discharging water you’ll need to check that the gauge and sender are a matched pair or an aftermarket package. By matched pair I don’t just mean both from a Ford. Even within manufacturers they can use different voltages for instruments. Although the car is 12v the gauges often run 7/8/9 volts only, and the variable resistance (the sender) is matched to this. Many cars need a voltage regulator to stop fluctuations and this must be earthed to work properly, something often overlooked in that glass or wood dash.
So we’ve established it is actually overheating so what’s next? Firstly pull the thermostat and replace with a new unit. Not running a thermostat? Why not? They are there for a purpose and leaving it out can make bleeding the system very difficult. Choosing a stat with a lower opening point is often all that is required to stop a car overheating, as the rad is adequate if the water is introduced at a lower temperature.
Bleeding a rad can be a problem, particularly if the rad is lower than the highest part of the water system. In cases such as these you need to add bleed nipples, expansion tanks or filler openings higher in the system. Assuming you have a standard type set up, fill the rad until it just covers the tubes and start the engine, from cold, with the rad cap off. Run it like this until it reaches normal running temp and the stat will now open. What happens is that any trapped air will rise and be trapped behind the stat and as it opens it will be discharged to atmosphere. Stop the engine, top up to normal level and refit the cap. Some rads, especially those with large top tanks, will discharge water when run again for the first time. This is due to the system needing an air expansion gap in the system. You could in this case utilise a blanking cap on the rad with an expansion bottle fitted with a normal pressurised cap.
Should the rad still discharge water after a new stat and bleeding the system, the next logical action would be to have the water tested for carbon dioxide, by a simple dye test, available from most local garages. If this proves positive you then need to examine for head gasket or, god forbid, cracked blocks.
If it’s a new rad fitted that is overheating after all the above checks are in order, you’ll need to put a 50/50 antifreeze mix in. Anymore will cause overheating as a higher percentage will not despatch heat a well as plain water. Follow this with a stat that opens at a lower temp, ensuring that all air that is available is forced to go through the rad, rather than around, and if using an engine mounted fan, use an up rated unit and a purpose made cowl unit. A higher pressure rad cap will raise the temperature at which the water boils. Don’t forget that a rebuilt engine can generate up to 25% more heat while running in. Once the engine is run in and the problem still persists the choice of rad needs to be re-examined. Do not run a new engine at a constantly overheating temperature as this can cause heat seizing and damage to the bores.
So you’ve got this far but you’ve bought the car like this and aren’t sure if the rads up to it. Let’s look at how to assess if the rad in there is any good. Firstly all the fins running across the rad should be there and in good condition. Just because it’s not leaking doesn’t mean its any good! Stroke the fins lightly with the flat of your hand. If they remain firm and upright – good. If they start to fold over and look green/orange there’s not much time left and if they just crumble, even in a small area its shot. Now, just because the fins remain upright doesn’t mean it’s doing the job. The next test is to check that the rad isn’t choked and will flow as per spec. Cross flow rads, (tank on sides) are very prone to areas of still water and blocking. The rad needs a flow test and this isn’t something that can be done at home. Even if only 5% of the tubes aren’t choked a garden hose will still flow at the same speed. Radiator shops use a large bore large volume pipe that recreates the pumped flow of an engine. They also heat the rad to working temperature and test by filling with air and inserting under water. This will show up troublesome small leaks that can cause water loss and ingress of air into the system. If the shop or garage want to do a “pump up” pressure test be aware that often this can seal the leak as they apply too much pressure. A soldered tank joint is always more forgiving than a crimped unit and excess pressure will cause these to peel back and, once the pressure is released, to leak or in extreme cases, fall off!! With large header tanks its best to use an expansion bottle as well due to the fact that repeated flexing will cause fatigue and splits.
If at this stage you realise it’s the rad that’s inadequate see my previous article on selection of the correct core. Other than that it may be a design or piping faults and, if you can find me at a run, I’ll willingly have a look at your set up. If all else fails don’t forget even air-cooled cars can overheat!! Won’t cure your problem but at least your not alone.
Kev Rooney