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MG MGB Technical - Engine overheating

I recently bought my 1970 MGB and have installed new plugs, points, condenser, adjusted valves, etc. Since the weather has warmed up I notice the engine gets warmer that I like (almost to the maximum mark) when I am driving around town. I have set timing to specs and when I am on the road I have no problem. It happens in stop and go traffic. Thinking I may need to have the radiator "rodded out" and see if that helps. Also planning to install a coolant overflow reservoir. Any thoughts?

John
John King

Hi John.

Quite a common problem, there is LOTS about this in the archive.

A gunged-up radiator is quite a common cause.
Some people fit upgraded rads.

HTH.. Don
Don

John. Y'all anint in yankee land where these here cars was made to run. Deys runs hot in this here SouthLand. (Just to show that, I, too can speak another language and "Ebonics" is not the only variation produced on the English language.)

Here in Arizona, the temperature gauge regularly shows 3/4 or higher during our summers. When in stop and go traffic, the indicated temperatures can run almost to the H mark with some minor rough engine running. All of these seem to be fairly common "problems" with MGs.

My solution has, so far, been to run a 25% anti-freeze-75% water mixture (more efficient at transferring heat away from the engine than a 50-50 mixture). A 160 degree thermostat (might not actually help all cars, but does not hurt anything in summer and it may help some cars). A flushed cooling system, good water pump, good pressure cap, good hoses and a pressure test of both the cap and cooling system.

Steve S. has been gathering information about the use of the Modine radiator cores in the MGB, attempting to come up with the "best fits" for the various years. The Modine core has been tried by several people, over the years, all reporting good results. So bottom line:

MGBs run hot in summer as the outside air temps rise. If the outside are is over 80 degrees F and you are not seeing some higher gauge readings, be concerned. How hot the engine can get and still not show damage has not been determined. Boiling over of a properly cleaned, inspected and set up cooling system is a bad thing. Regular running at 3/4 to 7/8 of the gauge, without boiling over, does not seem to have hurt my 68 GT for six+ years now.

You can optimise the cooling system, including trying Water Wetter (some find it works, some are less sure) and, if you wish, have the radiator re-cored with a more efficient core. But, for right now, you may simply want to observe and see what is happening and whether the system is boiling over. Les
Les Bengtson

Les and Don are correct. Just keep in mind that an engine is not overheating as long as it is not boiling (steam coming out) or the engine is not missing while the car is moving. My one point of disagreement with Les is the thermostat (and this is a very minor point), the thermostat only sets the minimum temperature that the engine will run at and has very little to do with the maximum temperature. The maximum temperature is determined by condition of the cooling system, including the radiator and the cooling passages of the block, the timing and the general health of the engine. I run a 195° thermostat in our MGB year around and the temperature goes right up to 195° and stays there unless we are in very heavy summer time traffic down in southern California or going over long, steep grades. Even then it has never gone above around 210° and has come right back down to 195° when the car is again moving on level ground. The lower temperature thermostat will allow the engine to cool down further when the load is removed if the conditions of the system is such that it will run cooler. There is a point, however, where the engine will be running too cool, which will cause poor running and excessive wear. Our MGB doesn't like to run well below about 185°, which is why I keep the higher thermostat in, allowing the engine to reach operating temperature quicker.

I don't have the exact figures for 25% anti-freeze mixture, but at 33% and in a system pressurized to 8PSI, the boiling point is 240°. Below that point, you are not going to do any damage to the engine. The pressure of the system actually affect the boiling point more than the concentration of anti-freeze.

I don't think that you will find any shops today that will rod out a radiator (it is an expensive and iffy procedure). Most will re-core the radiator and this is fine as long as they use the correct core. The Modine 4 row, L type core is the correct (and original) core to be used. Modine now has a upgraded core that works very well according to all reports, but I don't know what to ask for on that one (perhaps Steve S. can tell you). A definite DO NOY DO, is to replace the radiator with one of the replacements sold by Moss or Victoria British even though they are cheaper than a re-core. These replacements are junk and will really cause a overheating problem.

Another thing that some people have been doing to good advantage is to install the blanking sleeve (available from Moss) below the thermostat to block off most of the bypass flow. The original thermostats in the MGB (no longer available), came with a sleeve that blocked off bypass flow when the thermostat opened.

Regarding a coolant overflow reservoir, unless you are worried about the environment (and want to keep coolant off of the pavement), don't bother. If you are talking about a coolant recovery system, that is a different story. A coolant recovery system will catch the coolant that is expelled when the system is hot and allow it to be drawn back in when things cool down, thus keeping all the air out of the cooling system. It works much the same as a expansion tank, but does not require a pressurized reservoir. I can send you information and some pictures on a recovery system if you are interested.
Good luck - Dave
David DuBois

I to had the same problem. My gage ran just below red on my 1977 mgb .I have a 160 stat a rodded out Radiator new water pump, new hoses, and properly tuned motor. And it still runs just below red only when the out side temp is higher then 85 or 90 degrees. With lower temps out side it will run at ½.I had the great fortune to take my car to Less and he put a infer red temp gage on my motor. And we discovered the just below red on the gage was a reading of 183 degrees. For my own sanity I put in a after market temp gage with its own sending unit. And now can watch my temp by the number reading not low mid high. I have found that it will run at 185 normal operating temp and rise to 190 – 200 when the engine is shut off. It is a great comfort to read the numbers.
Gerry. www.gerrysmgb.com
Gerry

John. Just had to make a trip in the 68GT. As mentioned, I run the 25%AF-75% distilled water mixture. Outside air temp is 103 deg F in my back yard right now. Temps on the blacktop roads are showing 120+ deg. Temp gauge was showing over 3/4. Use the infared thermometer that Gerry mentioned to determine actual cylinder head temps. The front was 187 deg. F and the rear was 189 deg. F. Coolest part of the radiator was 164 deg. F.

Since I am an "advanced hobbyist", I have been assembling some of this more "specialized" test equipment which is allowing me a much better understanding of what is actually happening. The infared thermometer I purchased was a $200+ unit from Snap-On. You can, however, pick up a significantly less expensive unit for about $70. (The $70 unit goes up to 500 deg. F, while mine goes up to 999 deg. F which allows me to check out the functioning of cat converters.)

Drain and flush your cooling system, use the 25%-75% mixture and you should have no problems. (If you are not aware, anti-freeze is only 60% as efficient at removing and transferring heat as pure water. A 50-50 mix of AF and Water results in a cooling system effectiveness of 80% as opposed to running pure water. The 25-75 mix results in a 90% system effectiveness, possibly even better if Water Wetter is used.) There is more information on my website, www.custompistols.com/ under the MG and articles section. That should answer most of your questions. Les
Les Bengtson

I've fought overheating problems too on
several cars (not just MGs). But John says
the temp. is ok on the highway, and much
higher in town. This problem sounds more
like insufficient cooling from the fan, rather
than a clogged radiator. (Although the radiator
is still suspect.) I assume the original mechanical
fan is in place.

Is the fan belt tight enough and not slipping?
(about 1/2" deflection at longest point.)
Is the fan mounted in the right direction?
Is the water pump in good condition?

If all the above check out, a new radiator core
might indeed be needed. I couldn't get the Modine
core supplied locally, but did get a Godan
"MX" core that works well.
Ronald

Probably the key things I have found for a an effective cooling system in the MGB are the following.

1) a cleaned out cooling system - passages clean, debris removed, even the odd bit of sand casting (for the blocks) reinforcement wire removed, should you find any. I have often wondered if the reason some folks have chronic hot running is because they were unlucky enough to have one of those MG engines that had casting debris in the coolant passages. You may not, but I pulled a 3" piece of casting wire out of mine years ago, and several others on this BBS have claimed to have done so too.

2) a properly working water pump of a good design. Generally, most folks have found that the OE cast impeller pumps simply work better and with less cavitation, etc than the cheaper sheet metal impeller units available from some suppliers. If you have an old cast iron unit, you can have rebuilt.

3) The use of a blanking sleeve with what is called a "balanced" type thermostat (a design marketed by Robertshaw (I think a number for them is 330 followed by the number of degrees Farenheit they open (330-195)

4) The use of a coolant with is largely water such as Les Bengtson has mentioned.

5) The use of an electric cooling fan rather than the mechanical ones. Why? because they force more cooling air thru the radiator at zero mph sitting in traffic than the engine driven fans do, thus helping to stave off the accumulation of heat even when the car is at rest.

6) An unobstructed air flow to the radiator (an open grille) and a means of causing a depression of air pressure under the car, so as to suck air thru the engine compartment. One good means is a front spoiler or air dam. I chose the factory design, but I am sure some of the other options can also do as good a job of pulling air thru.

7) the use of Water wetter if I feel the car needs some "headroom" in its heat transfer capacity. All the Water Wetter seems to do is to allow the water to not form bubbles on the surfaces it is trying to transfer heat from or to.

Bob Muenchausen

FWIW- Using the IR toy I snagged at Napa one day, I documented a 13 degree drop using water wetter. Had an existing (+/-) 50-50 mix in the rad filled to 1/2 way up top resevoir. Dumped in the Water Wetter, drove about 1/2 hour and noticed the temp gauge just to the left of the dots. Earlier, before WW, same day, same area, the temp was, as always on the x-flow, past mid-way to "Hot"-red. I say WW works. Vic
vem myers

Or you could just convert to an electric fan. If you buy a Kit from (for instance ) Kenlowe, you can set the temperature at which it cuts in. You could use a 'Pull' fan and replace the mechanical one, or a 'Push' type and use it as a backup- set the temperature at the highest point you feel happy with. About £110 over here I think.
Dave

If you replace a mechanical with an electric fan, be aware that not all MGBs have the same distances between the nose of the water pumps and the core of the radiator. Simply taking off the mechanical fan does not ensure you that you will have enough room to house a puller type fan installation in some years of MGBs.

I have been using a pusher arrangement out of the above necessity for some years, and altho I don't doubt that a puller would be better, at least the pusher has done the job asked of it with reasonable satisfaction even in 105 F weather here in the American Outback. FWIW.
Bob Muenchausen

This thread was discussed between 05/06/2004 and 07/06/2004

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