Quote:
Originally Posted by blueosprey90
Greg, I run a plastic radiator shroud on my MGA (stock puller fan) and it makes a big difference in how much air is pulled through when compared to no shroud - at least when the car is sitting still. At speed, I suspect it has less effect since the air is otherwise being pushed through the radiator by the car's movement.
My shroud and fan tip separation is quite tight, maybe only 1/4".
I can't remember what drives the water pump on my PV444, but assuming that your water pump is driven by a pulley, it might be worth considering a larger pump pulley. The theory is that if you slow down the water pump, that will slow down the water moving through the radiator and allow it to cool longer before returning to the engine. I suppose a whole course in thermodynamics would be necessary to evaluate flow rates, temperature differential and heat exchange, but I believe that this would work better at faster speed rather than slower.
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The observation about the spacing of the shroud relative to the fan tip is correct. If you have a large gap between the fan tip in the inner diameter of the shroud opening you reduce the effectiveness of the shroud.
In the whole B18/B20 overheating / running hot discussion, you need to differentiate between 'is the temperature gauge just reading high' and 'is it really overheating'. Really overheating usually means the pressure cap is releasing and you are dumping coolant, also known as a boil over. The B18/B20 temperature gauge measurement point is at the back of the head. The thermostat is at the front of the head at the outlet to the radiator. I have a B20E which also has a coolant temperature sensor at the front of the head for the fuel injection system and my D jet has been converted to digital EFI so I can log the actual front of head coolant temperature while driving. Based upon my temperature logs I can provide a couple of observations:
- Once I am above about 40 km/hr the front of head and back of head temperatures stabilize with the back of head temperature being about 2 C higher than the front of head temperature. I have the 82 C thermostat which goes fully open at 90 C. On a hot day, above 40 km/hr my coolant temperatures measured at the front of the are probably 89 - 91C.
- If I come to a stoplight, the back of head temperature starts to increase almost immediately. The front of head temperature will start to increase; but, typically levels off somewhere around 93 - 94 C. My electric fan switches on at around 92 C and on a hot day, if I come to a stop light after driving at speed the fan will typically switching on about 10 - 15 seconds after stopping. On a vey hot day with a long traffic light the back of head temperature can easily rise about 10 C relative to the front of head temperature reaching temperatures over 100C while the coolant temperature as measured by the thermostat is still perfectly acceptable. As soon as the light changes and I pull away the back of head temperature starts dropping.
So, just because the dash temperature gauge is going quite high does not necessarily mean that the engine is overheating. Most factory temperature gauges are designed to be slow to respond so that most of these temperature swings are not seen by the driver unless the car is sitting idling for a longer period of time or is in very slow moving traffic.
The temperature increase when the car comes to a stop and idles is pretty normal. It is a combination of two things, reduced air flow through the rad which is slightly elevating the general coolant temperature and reduced coolant flow through the engine which causes the back of head temperature to rise. I have confirmed the latter because if I increase the engine speed to about 1500 - 1700 RPM I can actually cause the coolant temperature measurement to drop because of increased coolant flow through the head. Based upon the latter observation, I think your suggestion to reduce the coolant flow rate through the head with a larger water pump pulley would be a bad thing.
The take away - is the engine really overheating or are you just getting that normal temperature increase when the car comes to a stop with the engine idling? If the car is not overheating / boiling over and the sight of the temperature gauge creeping up bothers you, you can do the dodge of opening up the interior heater valve and shutting off the heater doors which allows increased flow through the head and some secondary heat rejection through the heater. You can also put a mechanical by pass valve around the existing heater valve which allows increased coolant flow through the head via the external heater circuit without heating the car interior.