1979 MGB running "hot" (in a bad way)

I have a 1979 MGB with 35,000 original miles and I am the original owner. I live in upstate New York and the car is stored 7 month a year (the cold months). I have it regularly serviced from the dealer that I bought it from in 1979, and I drive it on sunny days for pleasure. (Not many sunny days in upstate NY). The elusive problem I am having is as follows: For the last couple of years the engine is running hot (the car doesn?t overheat, but it runs much hotter than normal especially at slow speed stop and go conditions).

I have tried all of the following with no results:

1. Flushed the cooling system.

2. Replaced the water pump and belt.

3. Replaced the heater control valve.

4. Replaced thermostat with a 160 stat.

5. Replaced all the hoses.

6. Replaced the radiator.

7. Replaced both electric fan motors.

8. Replaced the fan(s) control switch and relay.

9. Replaced the temperature sending unit.

10. Adjusted the timing to factory spec 10 degrees BTDC.

11. Replaced Plugs, Wires and Distributer Cap (all OEM).

None of this has solved the problem. I have a couple of ?new? ideas but I thought I would ask for some expert advise first. My first idea involves adjusting the valves (although I don?t think this will solve the problem, but what the heck?). My second idea / theory is that the exhaust is partially blocked. The current ?Midas? exhaust system (the second aftermarket system) has been on the car for 14 years. It looks new from the outside but who knows what?s going on inside. The original catalytic converter only has about 5000 miles on it. I took it off in 1980 (replaced it with a bypass pipe) and re-installed it several years ago. The car ran fine after that. So what do you guys think ? Should I invoke my lifetime Midas warranty or try something else ?

Assuming a new radiator cap was included, a pressure test of the coolant system is step 1, compression test would be step 2. You have had all the probable candidates taken care of. I fear it may be head gaskets.

If there are no signs of overheating or coolant loss (does it have a coolant recovery system, an overflow tank?) then perhaps the gauge itself is the problem. Do the cooling fans operate normally? Why did you replace the fans if they were working??

It does havea coolant recovery system. No signs of leaks. The cooling fans operate normally. They were replaced at the dealers suggestion becayse they were almost 30 years old and he thought they might be running slow.

How do you know Midas will agree to cut the bait on your fishing trip?

Verify (with something other than the gague in the car) just what temp the car is operating at.

Exhaust back pressure can be checked without replacing parts…Usually, when this occurs, there is a very noticeable power loss. Overheating is not the main symptom. Especially at low/slow speeds…Put some tape over the gauge and drive on…Or try this. Make sure the gauge has a good ground and or hot wire connection. You said you replaced the sending unit, so it must be an electric gauge, right? My old MG had a direct reading mechanical gauge…

Stop throwing parts at it. Measure the ACTUAL temperature of the coolant. The gauge on the dashboard is ballpark at best, and may be faulty (it is, after all, an MG).

Besides measureing the temp (one of those infrared thermometers would be good for this) have you pressure tested the system and the cap?

I think a partially blocked exhaust system may, as others have suggested, be a place to look. The fictional mechanic, Gus Wilson, in “Tales from the Model Garage” which appeared in old issues of Popular Science magazine (1970 and earlier) found this the cause of overheating in an MG in one of the issues from the 1950’s or early 1960’s. I don’t know if these stories by Martin Bunn were based on someone’s actual experience, but it does sound plausible.

Can you get the exhaust off without ruining it to test your theory? OTOH, I would think that you would be way down on power & performance if you had a blocked exhaust. Adjusting the valves? Always a good idea on an MG . . . well, not adjusting, but checking and then if needed, adjusting. My mind goes cloudy on some subjects (maybe because the MGs that I owned were a source of constant repair), but I recall valve checking/adjustment was critical, and even then were prone to more than average valve job service. One more thing . . . not mentioned anyway. How are your brakes? Dragging perhaps? A car that sits around for most of the year might have a problem with dragging/partially engaged brakes, both primary and parking. Also not mentioned is air flow to through the grill . . . is it blocked at all? You covered a lot of the basic stuff, just thought I’d mention a few more. Rocketman

Thanks, you sparked an idea. With everything else I replaced, I never replaced the radiator cap. The system always seemed to have pressure so I never thought of replacing the inexpensive cap.

You’re right. This seems to be a theme in many of the replys. I need to get the actual collant temp wuth a reliable instrument. Most of the parts I replaced were 30 years old but not necessarily bad. OK I’m done fishing, Thanks.