Overheating in DOHC Engines
Cooling system (rewritten & partly due to formula error)
This article appeared in the Mirafiori forum June 16 and was in response to various ideas on the effects of unleaded gas in the dohc engine. The text is by Guy and is used with his permission
You do need a stat, but I like a low temp one, I suggest a 74-75 deg C type, (F = (9/5 * C)+32 = 167F) otherwise the flow round the head will be poor, ie: just come straight out the front. It acts as a restrictor you see. Moreover you damage the bores and rings on warm up without one. I can only speak about what I have tried and tested.
Remember for everything I write there will be other views as to what is best. No problem. I can only speak about what I myself have tried and tested. I cannot guarantee that if you copy my methods the friendship between you and ‘il motore’ will be idyllic - but it won’t go catastrophically wrong!
- Coolant - water wetting in the head (use glycol or wetting agent to prevent nucleic boiling). If you want your cooling system to stay in pristine condition use only genuine Fiat Paraflu at 50% mix and change it each two years. That stuff is amazing; I have seen heads run for 25 years in MINT condition with it.
- Radiator efficiency - bigger is better usually if your engine has more than 20% more power than standard and in my experience an alloy one made up to suit the architecture of the car is best of all but it mustn't be so big it over chills the coolant. The hotter the ambient, the more cooling area it needs. The
- The behaviour of the auxiliary cooling electric fan or whatever the engine has to cool the rad in traffic and its thermostatic switch – if fitted. Personally I like an over-ride switch and a warning light to tell me its running. Over about 30mph it should NOT be running because the mass of air from the car motion is enough to cool the rad.
- Hose losses - short smooth hose or alloy tube is far better than long runs of crinkly stuff. The fibres in hose do fatigue so don’t trust old ones, and always use top grade hose clips. Don’t forget the heaterhoses will dump your coolant just as effectively as radiator hoses.
- Airflow into and OUT OF the rad. The whole underhood is a high-pressure zone, without venting in exactly the right places no rad will work effectively. Vents below the windshield - in the scuttle region eg, don't work because that's a high-pressure zone, that's why flies get stuck on your windshield.)
- Oil cooling - oil helps to cool the engine and if the oil cooler suffers loss of airstream it will add to the general engine temp problem. I recommend 85 - 90 deg C oil temp going into the cooler.