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MG MGB Technical - Cooling Systems Problems? - Possible Solutions

This forum has been a great help to me in that past and I would like to contribute the following article.

Cooling Systems Problems? - Possible Solutions
MG “T” Series, MGAs and early MGBs

MGs in general are notorious for having cooling system problems. The original design was, at best, marginal, even for the cooler climates of the United Kingdom. These cars when driven in the southern third of America or in modern day traffic, anywhere, will likely experience overheating problems. So, what can be done to improve the overall cooling efficiency of the system? Before you begin to make improvements you must first verify that car’s radiator is clean, the hoses are leak free, the fan belt is tight, all ensuring that the stock cooling system is operating at maximum efficiency. Additionally, be sure that the timing and carburetor air/fuel ratio are set correctly as these too, will influence engine-operating temperatures. The improvements that can be made are as follows:

1. The most effective, but most costly, modification is to re-core the radiator with a modern high-efficiency 3-row tube design core replacing the stock two-row design. This greatly improves heat transfer and will, in itself, likely solve your overheating problems. Most radiator shops can re-core the “T” Series radiators. The downside is that it will require the removal of the radiator and will cost upwards of $400.
2. If your car’s only problem is overheating when operating in slow or in bumper–to-bumper traffic but otherwise okay, then a replacement fan may solve your problem. My understanding is that the 7-blade plastic fan (Moss p/n 434-340 - $76.46 at LBC) that is used on later model MGBs will fit the “T” Series cars. I do not have any personal experience with this fan, but it appears to be a sound approach to solving this specific problem.
3. The most cost-effective modification that you can make is to convert the current “open-to-atmosphere” cooling system to a pressurized coolant recovery system. Please see Building a Pressurized Coolant Recovery System” below. Water boils at 212 deg. F or 100 deg. C (Higher, with antifreeze added, but for the purpose of this paper, we will assume that water and the water/antifreeze mix coolant boils at the same temperature).

If, under all normally encountered driving conditions, your car operates at less than 212-degrees F, the open system is just fine. However, if on occasion, you exceed 212 degrees by even a small amount, the coolant in your radiator will boil, the steam generated will vent to atmosphere and when the engine cools it will contain less coolant and, hence, less cooling capacity. As this cycle is repeated, boiling will occur earlier in the cycle and with a greater coolant loss. If you do not top-up your radiator at frequent intervals, overheating will surely occur.

In an even worst scenario, assume that your cooling system is marginal for your car’s typical operating conditions. On a very hot day, you are driving on the freeway at 70 MPH and the coolant temperature increases to 212 degrees. The coolant will begin to boil, and steam will be created. Steam, being a poor heat transfer medium will exacerbate the cooling problem and, to make matters worse, the steam generated will be vented, resulting in less available coolant and a lower radiator cooling capacity. If the car is operated in this high speed, high ambient temperature, steady state condition, engine-operating temperatures will continuously increase and continuous coolant loss will occur. Unless you notice that the car is overheating and pull over to let that engine cool you will shortly exceed the critical temperature and the engine will seize. A very costly repair!!!

How can a pressurized coolant recovery system help? This type of system, in use since the 1960s, performs two functions. First, it pressurizes the system and second it allows for coolant that would normally be lost to be recovered. By pressurizing the system, to say 7-PSI to13-PSI (typical radiator cap ratings) above atmospheric pressure, the water’s boiling point will be increased to between 233 deg F to 246 deg. F. Additionally, when starting a cold engine and as it warms and reaches its normal operating temperature, the coolant in the radiator will expand. The expanded coolant will create positive pressure in the radiator and open the radiator cap’s bypass valve and coolant will flow into the car’s radiator coolant expansion tank (aka - radiator overflow tank). Later, when the engine is shut down and allowed to cools, a strong vacuum will develop in the radiator that will open the secondary bypass valve in the radiator cap. This permits coolant to be sucked back into the radiator, thus replenishing the coolant level. This cycle is repeated trip after trip.

With occasional minor overheating, the increased boiling point of the coolant will eliminate the generation of steam and, hence, minimize permanent coolant loss. The result is less frequent radiator top-ups and the reduced probability of future overheating problems.

If a temporary problem is present or if ambient temperatures are extremely high (e.g. a worst case scenario), the pressurized system will allow the engine to operate and an elevated temperature above the coolant’s normal boiling point. If the engine can reach an equilibrium temperature of 220 deg F or less, the engine will operate without catastrophic damage. Ideally, an engine should operate in a temperature range of 180 to 200 degrees. The occasional operation of up to 220 degrees is not desirable, but a far better alternative to overheating and an engine seize up.

4. To help detect a real-time overheating situation, you should consider adding a visual and/or audible alarm system. On my TD, the radiator has a 3/8-inch NPT (tapered) female fitting installed on the engine side or the radiator. I used this fitting and installed a temperature sensor normally used operate a modern-day temperature controlled, electric cooling fan. The sensor has an internal switch that closes at 204 deg. F. The sensor is wired to a dash light and a mutable alarm. If I am not attentive to the temperature gauge, the high-pitched alarm will certainly correct that situation. There are, of course, other ways to accomplish this idea. The objective is to install a sensor/switch in the cooling system and wire it to at, least, an audible alarm.

The temperature sensor switch that I used is NAPA P/N FS116 - $34.99. This switch has a 3/8-inch straight thread. It works, but you will be better off if you can find a switch with a tapered pipe thread. The mutable piezo alarm that I used was purchased from www.floydbell.com , P/N OC09-530-QO – $28.42.

(PS – I installed one of these alarms in parallel with the low fuel level warning light. I now have an audible and visual warning when the fuel level is low)

5. One last suggestion; there is a product called Water Wetter, made by Redline and available at Advanced Auto, Amazon.com and other places. The manufacturer claims that, when added to your radiator, your car will run up to 30 degrees F cooler. I don’t believe 30 degrees, but online testimonials claim actual cooler temperatures. It is most effective when used with water only (e.g. no antifreeze). It is supposed to contain anti corrosive and water pump lubrication agents. I have no personal experience with Water Wetter, but for under $10.00, it may be worth a try.



Building a Pressurized Coolant Recovery System

The design objective is to construct a small sealed chamber that can be pressurized by the stock cooling system. This pressurized chamber will act, in many ways, like a miniature radiator. Also included is a radiator coolant expansion tank that will store the overflow coolant.

The items required are as follows:

1. Two 2-inch copper plumbing end caps.
2. 3-inch section of 2-inch copper pipe. (Items 1 and 2 are used to make the pressurized chamber and can be purchased at a commercial plumbing supply house.)
3. Standard, small or large size, new or used brass filler-neck for a copper/brass radiator.
4. Mounting bracket made from a 1”x3” strip of brass or steel sheet metal with screw mounting holes drilled about 1/4-inch from each end.
5. 7-PSI to13-psi radiator cap, sized to fit the neck.
6. New or used small size coolant expansion tank. (A junk yard is a good source)
7. 2-inch length of 5/16”-copper tubing.
8. Two lengths of 5/16”-rubber fuel line (length to fit) and 4-hose clamps and a length of rubber tubing for the expansion tank’s outlet to atmosphere


To construct…

1. Drill a hole, with a size that matches the diameter of the radiator’s brass filler-neck (item3) in the flat end of one of the 2-inch copper end caps. (A spade-type wood boring drill bit will work)
2. Place the end caps over the copper pipe and solder together.
3. Drill a 5/16” hole in the side of the end cap without the hole for the radiator neck, about a ½-inch from the end. (This assumes that you will be mounting the chamber upright. If you are going to mount the chamber on its side, drill the hole in the bottom of the end cap)
4. Insert the 5/16-copper tubing (item 7) in the hole about half way and solder in place.
5. If mounting upright, solder the sheet metal mounting bracket (item 4) to the bottom of the chamber and centered on the end cap.
6. Insert the radiator neck (item 3) through the hole in the top end cap and solder in place.

The pressure chamber is now complete.

Assemble as follows:

1. Mount the pressure chamber at a convenient place in the engine compartment. I mounted mine on the topside of the passenger side frame rail.
2. Mount the expansion tank in an inconspicuous spot. On the front and right side of the toolbox, the backside of the frame cross member, just below the radiator are good places.
3. Using an appropriate length of rubber fuel line, connect the end of the radiator’s stock 5/16” overflow pipe to the 5/16” copper tubing installed in step 4 above. Secure in place with hose clamps.
4. Connect the Expansion tank to the 5/16-inch inlet/outlet pipe on the radiator neck (item 3 above) using the appropriate length of fuel line and secure with hose clamps.
5. Fill the expansion tank to the cool level mark. Fill the radiator to the bottom of the filler neck. Screw the original chrome radiator cap onto the radiator and the new 7-PSI or 13-psi radiator cap onto the copper pressure chamber.


You’re Done!!! Happy Motoring!!!

PS – If you have any questions, please call me at 843-838-0822 – Frank Grimaldi
Frank Grimaldi

"MGs in general are notorious for having cooling system problems. The original design was, at best, marginal, even for the cooler climates of the United Kingdom. These cars when driven in the southern third of America or in modern day traffic, anywhere, will likely experience overheating problems."

I really must dispute this. I've never had the slightest problem with my roadster in the UK or France in temperatures in the 90s, mostly with a rally plaque in front of the grill, and that is with the standard 3-bladed fan. Whilst I have no personal experience I know many people use MGBs in desert states and similarly have no problems. That isn't to say that *no one* has problems, some do, but it is a tiny proportion of the 500,000 cars sold and has to be down to faults and not design. Having said that rubber bumper models do seem to run hotter, but the later versions with the electric fans shouldn't have any problem, and should be capable of dealing with hotter conditions than the chrome bumper cars.

As far as coolant recovery goes if you are losing coolant you have faults or are over-filling it. In any case a coolant recovery system doesn't need to be pressurised, a simple catch-bottle with the standard overflow pipe going down to the bottom of the bottle and the original style of radiator cap is all that you need. As the engine cools down the low-pressure recovery valve in the cap will open and suck any coolant back up and into the radiator. I did have such a catch bottle on my V8 for a while as it was losing coolant due to a fault, until I resolved that fault.

I tried water wetter in my V8 but saw no difference on the gauge. I also fitted an up-rated radiator to my V8 (as cooling *is* more marginal on that than the 4-cylinder, but again mine never lost coolant purely from ambient temperature conditions even though it got as high as the red) but going from a 2 row to a 3 row or a 3 to a 4 isn't going to get you a mathmatical improvement. It is much less than that as it is the first row that provides most of the cooling, the next low significantly less and so on as progressively hotter air is being passed over them. On the V8 it made little noticeable difference. The biggest improvement came from improving the electrical connections to the twin fans, including adding local grounds at each fan where it mounted to the slam-panel rather than relying on the rather thin, long earth wire running back to near the fusebox. On the roadster fitting the foam seal to the radiator diaphragm made a noticeable difference to the temperature on the gauge in hot weather.

My 2 penn'orth.
Paul Hunt

Has anyone ever fitted a fan on their oil cooler in an effort to keeping the engine cooler rather than heavily modifying the water cooling system? If my system was stock and wasnt cooling effectively, and the engine was running well (Which was the case for me up until recently) Id first try and flush the system and get everything clean. Then I'd check the water pump for damage. (I did both of these things and now my car is spot on). If that didnt work, I'd try uprating the fan with a modern electric one, cause the stock electric one on mine for example leaves a lot to be desired, and sounds bloody awful when it turns on too. If that still doesn't work, then I'd start looking at uprating the oil cooler and putting a fan on it.
Ross Kelly

I fully agree with Paul regarding the cooling systems of MG being marginal. What people seen to overlook when they do have problems with the engines "overheating", is that they are driving a used vehicle that beyond being well used has probably been abused by lack of maintenance over the years. Any vehicle with a radiator that is 70% clogged and the coolant passages in the engine block obstructed with rust build up over the years is going to have a hard time shedding excess heat. The other thing that one has to realize, is that a car is NOT overheating as long as the coolant is not boiling (steam issuing forth and stumbling) while the car is moving, regardless of how high the temperature needle goes on the gauge.

The TC & TD could benefit from a pressurized cooling system, but our TD is run with a 50% antifreeze mixture, which pushes the boiling point up to 226°F and we have had the temperature needle on the dual oil pressure/temperature gauge nearly pointing into the oil pressure side of the gauge at times and have never had steam being coming out of the over flow tube or the engine start to stumble. This though is due to my having the radiator completely cleaned out and the engine coolant passages cleaned when I was restoring the car and making sure that I had the correct thermostat in place (I have more of a problem with slow warm up on cold winter days (even with a 185°F thermostat in place). As for the MGAs and early MGBs, they already have a pressurized cooling system and the same thing applies about having a clean, well functioning cooling system in place, including clan cooling passages in the engine block. Both of our cars have been driven in the hottest Southwest areas of the US on tours of the Southwestern US, where we drove the cars through deserts and over 14,000 foot passes during the summer months. The worst that has befallen us on any of those trips was a fouled plug on the TD one time.

I do agree with the addition of a coolant recovery system and have them in both cars, but they were installed as a convenience for checking coolant level than an attempt to combat over temperature conditions. I do like Frank's idea to pressurize the TD's cooling system and may try to incorporate that if I can find the required parts. Cheers - Dave
David DuBois

Cars with mechanical cooling fans already pull some air through the oil cooler before it goes through the radiator. Cars with electric cooling fans and the under-slung cooler don't have this, and in fact when stationary hot air from the engine compartment can only escape downwards, and a fair proportion of this comes forwards so the oil 'cooler' is sitting in *heated* air. It is this that contributes to falling oil pressure when idling for a long time, although it soon comes back up when you get underway again. It makes the oil cooler even less relevant on these cars, they were only provided as standard anyway to counteract complaints of oil pressure 'problems' on early cars.
Paul Hunt

So what do you reckon then? Is the oil cooler surplus to requirements and doesn't really do a lot? Or is it worth upgrading the oil cooler to a larger type possibly with a fan?
Ross Kelly

The existing cooler is pretty pointless in the UK and Ireland. A larger cooler, and especially one with its own cooling fan, would be even more pointless. If anything when people make changes to the oil cooler it is to fit a thermostatic valve to take it *out* of circuit unless really necessarily. And even then the benefits are marginal.
Paul Hunt

I have to agree with Paul, MGB cooling is a perfectly adequate system - if maintained properly.

British cars were once a mainstay of Australian motoring, well into late 50s early 60s. Certainly handled a range of temperatures here from extreme summer heat to winter alpine snow conditions.

My B runs at just a degree under N on the temperature dial since I poked around in the water passageways at the back of the block and moved a good deal of wet sludge-like material. I would rather it sat where it once did, centred on the N. I am considering some strategies to try and bring that about.

On the oil cooler, I tried my 69 without just last year - late Autumn to Spring/early Summer. Certainly my oil was running hotter, the oil pressure dial showed a tendency to swing from hot running (60-65) to hot idle (20-35)for the very first time in the eight something years I have owned it. Frankly, I got a little woried by the mid Summer at some of the shut-down sounds coming from the motor - suggestive of bearing 'rattle'. I chickened out and re-installed the oil cooler.

Sounds have gone away (crossed everything here!!) and oil dial has returned to its more limited range of movement. My thinking is that, given our summer temperatures here (up to 40C odd at extreme end), I will probably keep the oil cooler in and blank in full or part for winter running. I may use a slightly 'thinner' oil in winter to enhance flow at the lower temperatures.

Regards
Roger
Roger T

This thread was discussed between 26/05/2008 and 30/05/2008

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