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MG TD TF 1500 - Overheating, carb damper caps

Took off in the ’53 stock TD this morning at about 10am for a drive up the side of the Blue Ridge Mountains and down the Blue Ridge Parkway. Granted, by the time we (about 40 LBCs) started really climbing the ambient temp was up to about 94F but still I felt that I should have been able to make it up the 7-10% grade switchbacks without any problems. Ahh, but not to be. After the first good long pull the gauge was reading around 225F and I was beginning to worry. I pulled over, shut it down and opened the bonnet to let it cool down. After the gauge dropped to about 195F I opened the cap and added about ½ gallon of water to top it off (I had topped it off with 50/50 antifreeze just before starting) and took off to complete the climb to the top of that section. It made it to the top of that section but on the next steep part it again overheated. I tried running in 2nd gear to reduce the load on the engine and increase the fan speed but when the gauge again hit 225F I chickened out and pulled over again. Lots of boiling and water spewing out of the overflow. Cool down for about 10 minutes and added another ½ gallon of water. That got me up to the Parkway where the climbs aren’t as steep and we made it to the Pisgah Inn for lunch and a well deserved cool adult beverage.

When I got back to the car to add another quart+ of water I noticed that both carburetor damper caps had come completely unscrewed. The car had been, except for the overheating, running fine so my questions are (I’ll address the cause of and remedy for the overheating later):
1. Why would overheating cause the carburetor damper caps to unscrew?
2. Would the damper caps being unscrewed cause overheating (I can’t imagine that to be the case but I’m just asking)?

The total drive was about 150 miles and the drive back was 80% downhill so the car ran great and the temp remained stable all the way even at 60mph on the open highway in 94F ambient.

Thanks for your thoughts. Jud

J. K. Chapin

Maybe it was just one of those unrelated coincidences because after the 70+ mile non-overheating drive home I found the damper cap on the rear carb had come unscrewed again. So the real question is, why do the damper caps come unscrewed? Thanks. Jud
J. K. Chapin

The caps do that sometimes when the threads get a bit of wear. It will not cause overheating though, just a possible brief and slight lean mixture on hard acceleration. Not enough to affect temperature. A bit of goo on the threads, or a bit of teflon tape, should keep them in place.

I've seen a lot of T-Types that overheat, and a lot more that run cool in all weather. There are many, many variables, but if the car never used to get hot then the very first thing I would do is have the radiator rodded out, or at the very least flushed. Beyond that a timing issue could certainly cause this. Check timing at 3500RPM and make sure you're advancing enough. By far, those are the two most common issues with running hot. It's also possible for the waterways in the block to get clogged up over a long period of time. Removing the rear plate from the head often shows the general condition of the block's ability to circulate water. And to a lesser degree, changing your ratio to 80% water / 20% antifreeze can make a few degree difference, although you will boil at a slightly lower temperature so maybe don't do this until you remedy the hot running.

With the comparatively massive radiator, TDs (as well as TABC) should not have problems with hot weather if all is healthy and clean. Good luck!
Steve Simmons

There is a hole behind the front and rear right side block core plugs that allows coolant to pass through the inner and outer water jackets. These can be cleared with a drill bit When these become plugged with scale and muck overheating can occur. I would also suspect that your thermostat may not be functioning properly. You can check it’s operation on a stovetop in boiling water. If it is an malfunctioning original I would also suggest an aftermarket thermostat housing made from stainless steel with a modern replaceable thermostat from Tom Lange or AS. Avoid housings made from aluminum as there have been recent discussions regarding corrosion and failures of these items in short order
W A Chasser

I have Tom's thermostat housing and a new thermostat but I'll check the 'stat anyway 'cause that's simple. I'm concerned about the flow through block and through the radiator and also whether the water pump is pumping efficiently.

Is there a reasonable way to test the efficiency of the water pump in situ?

Thanks.

Jud
J. K. Chapin

I think there is a water pump available in the U.K. with more vanes to move more volume.

No more info at fingertips.

Peter
P G Gilvarry

The upgraded impellers are bronze and have six vanes instead of four. One problem with modern thermostats is that they don't address the bypass like the originals. You have a gaping hole for water to bypass the radiator at all temperatures, which was designed to be blocked off by a sliding bellows. You'll get differing opinions on this, but when using a modern thermostat (without sliding bellows) I like to close down that hole a bit, and ensure there is a bleed hole in the thermostat itself. Or if in a warm climate you can remove the thermostat altogether and eliminate the bypass line completely, either with a solid gasket or a blanking plate. The less coolant you allow to bypass the radiator, the better your cooling will be in hot weather.
Steve Simmons

Remember, the faster you move coolant through the radiator, the less effective it becomes, in a running hot situation like this there is a strong possibility that the block has restrictions in it due to years of rust buildup. I have an International tractor that has no water pump or thermostat, it circulates by convection only, it will work all day in 95 degree heat and never run hot because the coolant circulates at a slower pace. Just sayin. PJ
PJ Jennings

Exactly PJ. Back in you younger days I helped a fellow a couple of years in racing his sprint car. Of course they used small block chevy engines and some guys would totally remove the thermostats and the engine would overhead. The fix was to put a brass disk in place of the thermostat with a smaller hole to reduce the flow and allow the water to pull the heat out of the cylinder walls. Higher flow isn't always better.

Respectfully
Bill TD24570
Bill Brown


Anyone have any experience with the Reproduction Radiator MOSS sells. Do they fit and is there an improvement in cooling because they advertise it as being a heavy duty core?
Richard Cameron

I agree completely regarding there being an ideal speed of circulation, except that the uprated vanes that have been available the past 20 years do not pump water too fast. My TC is currently running no thermostat and an uprated impeller, with bypass blocked off. It runs cooler than just about any other T-Series I've come across, and has handled 115F temps many times without issue. But the radiator is flushed periodically and the block was thoroughly cleaned internally at the last rebuild.

I also have an antique tractor which uses thermo-syphon, as well as a stock Model T. The reason these systems work so well is that the vehicles were designed for it, and with a lot of overhead. The tractor has a 120-pound radiator for a 2-cylinder (albeit 5.3L) engine putting out under 40HP, and 3" radiator hoses on both ends. The Model T has a radiator about the size of a TD radiator for its 3-litre 4 banger with a whopping 22.5 HP. So it's not just a matter of design, but also of power output versus cooling ability. If you removed the water pump from a T-Series M.G., it would definitely overheat. But open up the water passages 50%, block off a few passages to ensure water circulates fully, then double the radiator size, and it might be fine.
Steve Simmons

Is this(see attached image) the bypass that y'all are talking about blocking off to increase flow through the radiator?

Jud

J. K. Chapin

Yes, but I've found the easiest way to do it is at the upper elbow. Just change the gasket between the little elbow and the thermostat housing for a solid one. No one will ever know by looking at it that anything has changed. Or to clean things up and go away from factory originality, replace the little elbow with a blanking plate and replace the lower metal pipe in your photo with one that doesn't have the bypass portion. Or replace the pipe and two hoses with one solid hose. Or just remove the bypass hose and cap the pipe. Lots of ways to skin this cat.

BUT... don't do this if you have a thermostat installed. If you have an original type sliding thermostat then don't touch a thing, it's perfect already. If you have a modern thermostat then you can reduce the flow by installing a gasket with a smaller hole in it. But when the thermostat is closed (cold engine) you need the coolant to flow through there so don't reduce it too much. I don't know what the limit is before you create a problem, but I've heard of them being reduced by maybe 50%.
Steve Simmons

Interesting. This is the fitting that was on the car when I acquired it in 2012. I replaced it with the bypass pipe when I bought the new thermostat housing from Tom.

Jud

J. K. Chapin

This thread was discussed between 05/09/2019 and 07/09/2019

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