QuestionQUESTION: i just got a 1979 MG Midget 1500 4 days ago. on day one i drove it for approx 3-4 miles and it seemed fine, not hot. i noticed after that drive a small drip out of the hose that goes from the bottom of the carburetor to a pipe that runs along the block and tees off to the heating unit.the next day i disconnected leaking hose and got replacement because it was totally blocked with gunk. i also noticed that the part of pipe that is was connected to was also clogged with gunk. i cleaned it out. i lost some antifreeze during this process. i drove it after this change and it totally overheated about 2 miles down the road. i stopped and checked it out and a second hose was now leaking so i waiting for cool down and returned home and replaced that hose. i lost a little more antifreeze.(not a lot) since then, i cannot go more than 2 miles without overheating. the water pump seems fine as it is not leaking. the thermostat was supposedly changed recently by the prior owner and the radiator flushed. being that you cannot see into the radiator itself, i don't know how to tell if it is full. the metal expansion tank is half full and coolant looks nice and clean and green. i also removed hose from thermo housing to radiator and blew into it and got antifreeze out of thermo housing so i assume there is no clog there and should have flow.
so, what can i check next? need to figure out how/why it is running so hot. prev owner insists it never was hot. however i don't know how much it was actually driven since inspection sticker is from 1997. work done recently was, new altenator, new zenith carb, new fuel pump, new thermo, new air filter. please advise and i appreciate your help/advise/knowledge
ANSWER: Hi Cherie,
The procedure I use for testing for overheating is to first confirm the gauge reading. This is easier then it sounds. When the gauge reads hotter then normal just take a household meat thermometer and place the prob against the thermostat housing and note the reading. It does not have to exactly match the gauge but if it is just close and you are getting coolant in the overflow tank then go to the next check which is to get the dye from any auto parts store that tests for CO (carbon monoxide) in the coolant. The instructions will tell you what color you should see from the dye added to the coolant. This tests for any leakage of the head gasket or a crack in a combustion chamber.
Don't forget to check the fan clutch to see that it is not free spinning and not turning the fan fast enough. Also the fan belt tension. Another point is, did it overheat when driving on the highway or below 35 MPH on secondary streets? A faulty fan clutch will show signs of overheating at the lower speeds (Below 35 MPH) but not over heat on highway cruise speeds.
A sticking thermostat or a failed thermostat will cause overheating and you should not depend on what a former owner tells you. We often had customers come to us and say "They just installed a new thermostat so that is not the problem." We learned to test it anyway. You can test it by removing it and read the temp number printed on the end and suspend it in a pot of water on your stove top and with a meat thermometer you can watch it open and note the temp that it starts and is fully open. When fully open it should closely match the number stamped on the end of the thermostat. It should start to open about 10 to 20 degrees before the stamped number.
If all that tests ok and it is overheating at any speed, you should consider having the radiator tested and cleaned, also check to see that the water pump impeller is tight on the water pump shaft.
Other things we have found that cause over heating are, lower radiator hose collapsing, incorrect ignition timing and the carburetor mixture set too lean.
Howard
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thermo
QUESTION: thank you for your ideas/instruction. i have tested thermo and it works and i have a new radiator, hoses and thermo housing that will be in tomorrow and tuesday. i removed the old radiator and thermo housing cover and removed the thermostat. under the thermostat at the bottom of the thermostat there is a hole going down toward the water pump. there is some metal (possibly lead?) in that hole. i have attached a picture. my question is... is that hole supposed to be plugged up? is it supposed to be open? it that metal supposed to be there? should i remove it or leave it? and what is that hole from or too? what is its function?
AnswerHi Cherie,
I can't tell from your picture but there should not be a connection between the two chambers in the water pump housing that go into the cylinder head. You may have to remove the water pump housing from the head and look closely at the two chambers. One chamber should come from the lower radiator hose to the center of the water pump impeller and from outer edge of the water pump impeller and go to the Cylinder head. The other chamber should should come from the head to the thermostat housing and bottom of the thermostat.
Inside the water pump housing there must not be a connection between the two chambers. I can't tell from your picture but it looks like a second hole connecting the two chambers. You will have to pull that water pump housing off of the head and remove the water pump from the housing and look to see that there is no connection between the two chambers.
Howard
