All the original complaints about STAG Cooling system were probably justified and usually related to the fact that the sand cores was not always fully removed from the engine block after casting, and in use, ended up in the radiator. The other real problem was/is that the internal water pump is high in the block and if the engine has slight water loss, then the pump is left high and dry, the water starts to boil around the heads.
These problems are not aided by the inaccurate sensor/gauge and/or the high mounted temp sensor that ceases to read when the water level drops below the sensor level, or the nature of the aluminium heads themselves, which expand greatly when overheated. This expansion usually results in loss of head bolt tension and subsequent blown head gasket when refilling and re-starting. The must-do here, is to re-torque the heads if you ever boil a STAG, this needs to be done before refilling with coolant or restarting, also while success is not guaranteed, with easily accessible head studs and bolts, it is worth a try. Again remember to re-tension the inclined upper row of studs first, starting in the middle and working your way to the front and rear, then in a similar manner, re-tension the lower row of bolts, re-tension all to 65 ft/lbs. Cooling system problems we commonly find include:
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Partially blocked radiators, (when re-coring we recommend 3 rows of 16mmx3mm tubes, especially good for cars with AC, 5 row units can actually reduce the amount of air passing through.) |
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Missing original fan, often replaced with a smaller unit. |
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Missing Fan Shroud, we fit Fibre Glass Replicas which when painted look the goods and perform well. |
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Locked up fan after the viscous coupling has failed, (This locking up is often done by the owner who is reluctant to spend some dollars to look after a very expensive irreplaceable fan) this locking up often results in the fan throwing a blade as it attempts to run at engine speed. |
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Stretched neck on the expansion bottle. This allows coolant loss and a failure to hold pressure. Where this is a problem we fit an all aluminium tank, made to fit in the original position.(we use 15psi caps on all models) |
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Incorrect or missing thermostat, these units have a foot valve and some we have found fitted are too short, We use hi flow 82deg units, with the correct foot valve, these have a much greater opening and flow up to 50% more water than the original units. |
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Water Pumps, we often find that 6 vane units have been changed to 12 vane, however the 6 vane cover has been retained resulting in very high clearances and minimal water flow at low RPM. We find nothing wrong with 6 vane units, Actual inspection will show that these have less evidence of cavitation corrosion, so are probably a better unit as long as the vane-to-cover clearances are reduced, a similar storey exists for the 12 vane unit |
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We machine the cover for nil clearance and use a ten thou gasket to achieve a satisfactory fit. Often we find loose impellors and badly worn drive gears, but that's another story. |
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Temp Sensors and Gauges, when checked against our optical Laser unit we find wide variation on the results, even when new sender units have been fitted. We often add small resistors to the sender unit wire to bring the normal vertical needle point into position for the desired 82deg. reading. |
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Coolant, our systems are all old and probably come with a fare share of crud and oxide build up. We find Redline Water Wetter, used with demineralised/deionised water as an ideal coolant, we use no other anti-boil/antifreeze additives. The product works like the soil wetting agent used in gardening, reducing the surface tension of the water, and increasing the rate of heat transfer. A single Treatment lasts 2 years. |
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Other fixes can include the addition of a thermo fan, TR6 Spoiler, and don't overlook the advantages of adding an oil cooler. |
Our best success to date has been on a constantly boiling Air conditioned car used as a daily driver covering 40,000klms a year. After working our way through the fixes above, including the oil cooler, it now has no trouble coping with our summers and the stop start city traffic that the owner subjects it too.