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Cooling the T-Series Engine
by Skip Burns (TB 0304)

As a displaced San Diegan living in San Antonio, Texas my unique location in a hot weather region has provided some insights (and solutions) into the problems that plague our engines in hot weather climates. Summertime temperatures in Texas regularly exceed 100 ° Fahrenheit. Because the XPAG engine was designed for cooler United Kingdom temperatures—not the hot, arid conditions of the American West and South-west—our stock radiators and fans often fail to provide adequate cooling during the summer months.

Assuming the ignition timing is correct and that your car’s engine has otherwise been tuned properly, the principal parts that can cause overheating problems are the radiator, fan, and the exhaust manifold (vapor lock). Other causes like excessive rust in the cooling system, leaking hoses, etc., are beyond the scope of this paper. The intent here is to attack those areas that have plagued T-Series owners for years and which can be readily fixed.

Radiator: When I was racing my TB in England in the early ‘70s, the word was that our stock radiators were originally manufactured for light trucks. I don’t know. Perhaps the story is apocryphal. The point is, the stock radiator doesn’t hack it in the States. I changed out my stock radiator two years ago for a new, three-core, high efficiency radiator, even transferring the brass patent plate affixed to the back of the stock radiator from the old to the new radiator. The price was $226 (Alamo area price in December 1998). I defy anyone looking at it to tell the difference between the new and the old. Before then, it was common to see 90° C or more on the temp gauge during a hot, fast run. Several times, at parade speeds, I experienced boil over. Since installing the three-core radiator— and while cruising at speeds above 30-35 mph, even at 70 mph (where the fan plays no role)—the highest temperature I’ve seen has been 83° C and that’s on a really hot day. My stock thermostat is set at 72° C and that’s what I’m accustomed to. Ergo, go out and get a three-core radiator! It’ll solve most if not all of your cruise-speed heating problems. And don’t forget to tell your radiator specialist to maintain the original core’s length; otherwise, you may not be able to get the radiator cap on over the shell.

Fan: Ah, the fan, that puny stock fan—or what passes for one. Countless articles have been written suggesting various fixes. Before doing a mod to my fan, the water temp would literally shoot up at stop signs and in slow traffic. One mod I seriously considered adding a stock, non-offset blade to the existing pair of blades resulting in six, rather that four, blades. Skip Kelsey of Shadetree Motors has had one of these on his car for several years and swears by it, having driven his car all over the country without problems. But I looked at it and decided against it. Stock fan blades are subject to fatigue failures (Boy, do I know! I had one). Given a blade weight of about a third of a pound, when it fails, it’s going to do a job on your radiator and anything else that’s nested up front...with high odds for punching a new ventilation hole in your bonnet. In addition, installing the third blade required machine work, which I wasn’t up to. What I sought was something light that would pull heavy drafts of air through the radiator at stop signs and at slow speeds, and that wouldn’t require the skills of a machinist to produce; in other words, a bolt on-bolt off exchange fan. There’s good news. MGB fan (Moss Part No. 434-340/Rover Stock No. 12H 4744), is a plastic fan with seven blades. Here’s a comparison of your stock blades with the MGB fan blades:

                     Stock Fan          MGB Fan
Material             Steel                  Plastic
Blades               4 (non-offset)         7 (offset)
Total Weight         22.34 oz. or 1.4 lb.   6 oz. or 0.375 lb.
Weight Difference    Plus 1 lb. for the stock fan
Blade Weight         5.59 oz. or 1/3 lb.    0.86 oz. or 1/20 lb.
Blade Length         4 inches               4 inches plus
Blade Shape          Rectangular            Ovoid with flat tips
Blade Spacing        Regular                Irregular
Blade angle at hub   Less than MGB fan      Greater than stock fan
Blade angle at tip   Same as MGB            Same as stock
Hub thickness where  0.34 inches            1.215 inches
   blades attach

The irregular spacing of the MGB blades attenuates fan noise. The blade angles are (in degrees): 47.48, 55.92, 54.89, 47.64, 44.42, 63.78, and 45.87, respectively. The plastic is yellow. I painted my fan black.

This fan is a direct replacement for the stock fan on the TA/TB/TC (more about the TD/TF in a minute). The work is best done—troublesome, I know—with the radiator off; in other words, while your radiator is down at the shop being re-cored. Installation is straight forward, while taking note of the following.

The boss hole in the MGB fan fits nicely over the pulley boss with about 8 thou clearance around the edge. It may be that Rover is sourcing its fans in Taiwan, because the fan’s boss hole is not exactly round. Does this sound familiar? In any case, it doesn’t matter. What does matter is that the fan boltholes are centered precisely around the pivot point of the fan. Or at least they appear to be. And they line up nicely with the holes in the pulley. There are small differences, though. The plastic fan holes have metal inserts in them whose holes are slightly larger than the pulley boltholes. In addition, the radial distance of their respective holes from the central pivot point is different; the fan boltholes are a tad more distant. Closer investigation with the bolts installed reveals that their shafts butt up against the inner rim of the fan boltholes, centering everything up...well, almost. With the bolts loosely fitted, the fan can be adjusted slightly and moved a thou or two in one direction or another over the pulley boss. By tightening and spinning the pulley by hand (pulley installed), then loosening and adjusting as necessary, the fan can be centered within tolerable tolerances. I’m somewhat hamfisted, so if I can center mine perfectly—you can, too. Remember that this is a very lightweight fan, so being off center a thou or two shouldn’t create problems. When the installation is finished, don’t forget to check for any interference with hoses, etc.

With the radiator back in place, I was able to insert a 1/4-inch wrench with a 3/8 socket attached between the blades. Lock washers were added as a safety measure. With the bolts loosened, I was able to reach in and remove them by hand. When reinstalling the bolts, look for the bolt hole on the back side of the pulley boss to help locate your position. Perenthetically, using your fingers, the larger holes in the fan hub enable you to easily find (blind) the hole in the fan, then move the bolt around a bit to locate the smaller pulley hole. My hands are like catchers’ gloves. If I did it, you can do it.

I wasn’t able to check the MGB fan installation on the TD or TF. Given the thickness of the fan hub that holds the blades and the additional spacer on the TD/TF, the fan may wind up too close to the radiator. But I don’t think so. Eyeballing it, it looks like it will take the new fan with the spacer installed. If not, two alternative suggest themselves: 1) remove the spacer and see if the pulling power of the seven-bladed fan is still an improvement, even when farther away from the radiator; or, 2) reduce the height of the spacer to allow room enough to get your fingers and a 1/4-inch socket wrench with a 5/16 socket into the space. I leave it to a TD/TF owner to play with and let us know.

Vapor Lock: Leave the car in the parking lot for five minutes on a hot day after a long run and chances are the gas in the float bowls will have vaporized. The car may start, but you’ll wind up looking like a thirteen year-old learning how to use a manual clutch with the car bucking its way out of the lot as little drips of fuel get through the carb. Only when enough cooling air has passed over the carbs does the problem go away. There is a solution.

Any numbers of heat shields are available. I like the one from Brown & Gammon in the UK (email: The shield is made from heavy-gauge, machined aluminum giving it a nice, finished look. Copper riveted to the back is a thin layer of asbestos; itself shielded with a layer of aluminum. This is the layer closest to the manifold. The closest distance of the manifold to a float bowl is 1.2 inches, while the manifold clamp is even closer—just over a half-an-inch. Radiant heat is the main culprit here, as most of the conductive heat is blown away by the fan. As installed, a nice extra is the tunneling effect of the shield, keeping the conductive heat between the heat shield and the manifold and blowing it along the tunnel to the rear.

You may have to do a little Dremeling in spots, as the spaces in the shield through which the manifold clamps protrude aren’t quite large enough. Ten minutes with a Dremel are all that’s needed. In addition, the nut on the end of the throttle arm that connects with the bottom of the throttle link may hang up on the bottom edge of the shield. Don’t want any hang-ups there. Two fixes: Dremel a little vertical channel in the bottom of the shield to allow the nut to pass freely; second, move the throttle return spring clamp that’s attached to the inner bolt of the starter to the outer, right-hand bolt. If you keep it on the inner bolt, it tends to pull the throttle arm in toward the shield. Moving it to the right has the opposite effect. After doing this, you’ll find the throttle return spring too long. Any automotive store will have a throttle return spring that you can size to fit.

Finally, if you want to go the distance and fix all potential cooling problems, make two more changes. First, don’t use the Moss fan belt. It’s too short. Moss knows this but refuses to get the correct belt. Instead, order a belt (part no. 434-120; Goodyear stock number 22394) from Skip Kelsey at Shadetree Motors [(925) 846-1309l—email:]. This notched belt is slightly longer, moves your generator farther into the bulge on your bonnet and so, opens the space between the tach reduction gear housing and the distributor. Keep your belt loose—just enough to turn the generator—to avoid overtaxing the bearings in your generator.

In addition, consider installing a radiator overflow tank. I found a used MGB overflow tank—all brass with an inflow/outflow tube and an overflow tube attached. It holds 2.5 pints of water, more than enough. After wire-brushing all the crud off and repainting the attaching strap (don’t forget to get that, too), I polished it up and installed it on the inside, upper, forward edge of the firewall—in other words, at a 45 degree angle inside the firewall. It comes with its own radiator cap, so you must remove the rubber seal on the end of the cap to allow overflow water to escape out the overflow tube in the neck without pressure behind it. Route two hoses: one from the radiator overflow tube to the inflow/outflow connection on the overflow tank, another from the tank’s own overflow tube back out the firewall and down somewhere toward the tranny.

Making these modifications to your cooling system should make you, your significant other and your car’s engine very happy.

Cheers, Skip

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