Anything and everything Stag.

Engine, cooling system, fuel system, exhaust system.

I am just in the process of rebuilding my stag engine.The engine has never overheated but i am wondering how much cooler the engine will run if i fit an oil cooler. I am trying to justify the expence of fitting one as it is an expensive kit

David,
I'm no Stag expert, but....
Oil is meant to be hot! Too cool and it doesn't circulate properly.
IMHO, no one needs an oil cooler unless they race it.

John

Fitting an oil cooler will tend to make the engine run a little cooler (some air cooled engines were in effect at least 50% oil cooled!) BUT it is a poor way to tackle "simple" overheating. If the coolant temperature is getting too hot, it is a matter of coolant circulation (pump, silting etc), radiator size and airflow through it. Better to tackle those at source, and a number of proven solutions to that now exist for Stags.
However, although oil SHOULD be hot to do its job properly, it should not be TOO hot (max 110degrees C?) otherwise it tends to become too thin and need replacement sooner. However, this tendency is getting less with modern oils, and almost removed with synthetic oils.
If you only run relatively short journeys, and change your oil regularly, you probably have no need for an oil cooler.
BUT if you run a reasonable mileage on long high speed journeys, then it may well be desirable to keep the oil from getting too hot. If you fit a cooler, it MUST be fitted with a thermostat so that the cooler is not in circuit until the oil gets hot enough to need cooling! If you run with permanently overcooled oil it will cause as much engine wear as overheated oil. If you have a cooler with thermostat, it may not often open to cool the oil, but the fitment can do NO harm, and will do some good when it is needed to cool the oil. You will probably never know how often that is unless you have an oil temperature gauge (quite easily plumbed in when fitting a cooler) or by checking the temperature of the cooler hoses after a run to see if the thermostat has opened.
There is an alternative that some companies like Volvo and VW have used on a regular basis, that is, IMHO the ideal solution. This is an oil/water intercooler. This is a straightforward heat exchanger between the engine coolant and the oil. You can get LOTS of oil cooling by fitting downstream of the radiator, but most are fitted to the HOT side, or somewhere in the heater or manifold circuits. As the coolant warms up quicker than the oil, this tends to warm the oil up (a good thing) but as the cooling system keeps the coolant temperature below 100 degrees, prevents oil from getting too hot.

A Mocal Laminova oil/water cooler like this?
JOhn

That's one way to do it. However there are other much neater square box-shaped ones which fit between filter take-off housing and filter (VW type) or circular flat plate types between block and filter (earlier Volvos).
There was also similar neat one fitted to MG Metros.
These probably have a rather smaller heating/cooling surface, but this should be sufficient for road use rather than extreme racing.
I think that some of these "square box" ones are also used for auto gearbox oil coolers (as sometimes required for towing etc).

Now you just need to tap in to the cooling circuit and take a feed off to the washer bottle and we can kill two threads with one stone!

The ideal temperature for your oil in normal operation is about 90deg C. Any less and the oil is not circulating properly and will not do its job (increased wear). If the oil temperature is consistently over 110 degs C then the oil is likely to start to break down. In normal use on your Stag the lubrication system has been designed to cope with the needs of the standar engine and you should not need any extra cooling (nor is it recommended). If you race it or perhaps tow at the maximum towing weight then you might want to consider it. But even so, you MUST fit an oilstat to prevent running too cold. Ergo - it's not worth the cost for a standard car.

Well if you fit a thermostatic switch in the oil cooler circuit it will cool the oil to whatever the thermostat is set to.

To get back to the original question, Stag overheating resulted from problems with water circulation and cooling via the rad it wasn't really caused by overheated oil.

Auto versions have an oil cooler but that's for the gearbox.

If you want to ensure against overheating make sure the engine and rad are well flushed out, have no superfluous metal sand or any other residue of original or subsequent work and then repeat on a regular basis.

There are higher efficiency rads around and various water wetters and other additives that can help and also electric fans although the Kenlowe on mine seems to inhibit cooling initially until it kicks in. I ran into a traffic jam on the M25 with temp gauge almost in the red after cruising on the legal limit on a hot July evening but by the time I got off after 45 minutes in the jam(J23 to J24) the gauge was reading normal so I am not convinced how good they are.

Some of the problems with electric fans is their effect on airflow through the radiator when running at speed but without fan switched on. Apparently a "windmilling" fan can block a larger area of radiator from "proper" airflow than the physical area of the blades. (More like the area of the "outline" of the whole fan assembly?)
However, an engine block and its coolant are quite a large heatsink, and if suddenly deprived of airflow by reaching a traffic jam on the motorway (and with a lower rate of coolant flow through the radiator because of low water pump speed at tickover) there is suddenly a "backlog" of surplus heat to dispose of and this is the worst case scenario for any cooling system. It seems to me that your situation might be improved by lowering the cut in temperature of the Kenlowe. Once the fan is switched on, raising the tickover to perhaps 1200-1500 rpm by suitable application of right foot may help to bring coolant temp down a bit quicker.

CHris,
I'm sure you're right about the 'heat sink', though I think a better term is 'thermal inertia'.
And reaosn hwy an electric water pump may help. The mechanicla one is optimised to work at 3-4K, so circulation will be minimal at tickover. An electric pump, esp. if you run it with a thermostat, will kick in at optimal flow whenever indicated.

That, and 'thermal inertia, is another reason why an electric pump is a popular racing mod - you can leave it switched on after you stop, circulating water and preventing hot spots developing in the engine as heat soaks through into the smaller water passages, possibly boiling them.

John

Section : Engine

Fitting An Oil Cooler

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Fitting An Oil Cooler

Fitting An Oil Cooler

Fitting An Oil Cooler