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The engine generally ran too cool unless really pushed. Oil pressure was also quite high.
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Thus, the need for a thermostat.
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Regarding oil cooler thermostats, Revington TR specifically recommends against them. They question the benefit and reliability. Revington TR know these cars well.
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Yes, Neil makes an argument against oil coolers in general, not just thermostats. William's book (which, I agree w/you, contains a few errors and even opinions I sometimes have to disagree with, but is generally quite good) does present Neil's case: He prefers to add oil cooling in a more passive way by modifying the stock sump pan with a couple sizeable tubes running front to rear and welded in, increasing air flow and cooling.
However, done right this also means cutting holes in the structural frame cross member just ahead of the sump, in order to route air into those sump tubes. Since the large cross member supports the weight of the engine and the stresses of the front suspension, punching holes in it makes me a little nervous! And, while I would guess there's not enough cooling added by this method to cause a problem, there is no control over how much cooling is effected (as a thermostat would do). So perhaps in some situations over-cooling might occur. Finally, this method also reduces the amount of oil in the sump (unless it's bumped out to the side to add some capacity back, also).
Keep in mind that Neil's emphasis is on rally cars. He owns two of the four original factory rally TR4s, and has regularly competed in historic events with at least one of them. Rally cars are often driven on gravel and rough dirt roads, where an oil cooler that gets holed by a rock can knock the car completely out of the running. So, for this sort of competition, an oil cooler might not be the best option. Neil's exhaust systems and many of his other parts also tend to be designed from this particular point of view. I'm not suggesting this design and development perspective is a bad thing, just that it's something to think about in relation to how you will be using your car.
For example, folks like Kas Kastner, Ken Gillanders and many, many others - some of whom who have probably been building and working on TRs about twice as long as Neil Revington - all use oil coolers on these cars on a regular basis. Lessons learned while rallying might be very applicable to the typical driving experience on the narrow lanes and roundabouts throughout Neil's England.
The guys on this side of the big pond (Kas, Ken, etc.) generally built cars for endurance (Sebring) and SCCA road racing, which I would argue might be more applicable to driving in the U.S.
In really broad terms, I think there's a lot more cruising at sustained mid-to-high rpms in U.S. driving, while there's more working up and down the gears, accelerating and decelerating in Britain. Note: Although some have no posted speed limit, by comparison the "M" motorways in England are relatively new and nowhere near as extensive as the U.S. system of freeways and fairly high-speed secondary highways.
Also, ambient summer temperatures across most of the U.S. tend to be higher than in England. A *lot* higher in some cases.
All this steers me toward using an oil cooler (w/thermostat), but I would certainly agree with Revington on one issue: The older and still most common style of oil cooler thermostat is mounted inline requiring 4 additional hose connections in the cooler's hose circuit (for a total of 8, minimum).
Each added connection is an opportunity for something to loosen and leak. This is one reason I personally like the combined take-off and thermostat now offered by Mocal (part SP1T at
www.racerpartswholesale.com) which doesn't add any connection points, because the thermostat and bypass do their thing ahead of any of the hoses. Perhaps some other manufacturers offer something similar, I dunno. The Mocal is just the only one I'm familiar with.
Best case scenario, the thermostat works correctly and oil temps are kept within a more ideal operating range, helping maintain optimal oil viscosity, extend oil life and even moderate general engine temps to some degree. Middling case, an oil cooler thermostat fails closed: The oil bypasses the cooler and runs at the same temp it would have done without any oil cooler installed. Worst case, the thermostat fails partly or fully open and there might be some over-cooling of the oil for a while until the thermostat is fixed.
Oil coolers were factory/dealer options on all TR models, and are options or standard equipment on all manner of cars and trucks, both new and old. The technology has been around quite a while and is pretty well proven.
My biggest concern about an oil cooler is effecting a complete oil change. There will be some old oil trapped in the cooler all of the time (especially as it's now mounted on my car). But, on the bright side, the cooler increases the total oil system capacity a bit, which is never a bad thing.
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...the engine frequently ran too hot.... made an aluminum shroud to fit it, added an electric fan and punched louvers in the bonnet.
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Very interesting! So, in other words, improved shrouding, an electric fan and engine compartment venting worked well enough that the oil cooler (w/o a thermostat) was "overkill", even with a hotter/modified engine.... I'm making similar engine mods in my TR4, and will be going through the same sort of efforts to keep engine compartment temps under control. Glad to hear I'm on track!
Maybe when I get my TR4 back on the road, I'll buy one of those laser thermometer thingies and temporarily disconnect the oil cooler to measure the differences, and be able to give a more real-life comparison.
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