QuestionQUESTION: Hi Howard,
First I want to thank you for past answers to my questions. You have been very helpful.
I finally fired up my 1980 MGB after an engine rebuild. I have 2 questions:
1. After running for a few minutes, the temp gauge went to almost in the red zone and then I shut the engine off. The electric fans never turned on. I found a blown fuse which controls the fans - the spec says is 17 amp (35 amp blow). The local auto parts store doesn't have 17 amp fuses. Only 15 and 20. Would a 20 amp fuse be ok? Also would this blown fuse have anything to do with no heat getting to the heater. When I had the engine out I ran water with a hose through the heater core and it ran continous so it's not clogged. Is there air trapped in there or something?
2. I also noticed after running the engine for those few minutes that the coil was extremely hot to the touch. Is this normal?
Thanks for your help.
ANSWER: 1. A 35 amp fuse would be more appropriate. Install a 35 amp fuse and turn the ignition to "ON". Then short across the two pins of the thermo switch wires in the radiator to active the fans (Green to Black/Green)to see that they are operational. Recheck your coolant level as air pockets often cause problems on new rebuilds. The fans are turned on at 200 deg F and off when the temp lowers to 180 deg. F. As far as the heater goes you need to check to see that the heater control valve is opening. If you still have a heating of the engine problem remove the thermostat and look to see that it either has a small "jiggle valve" in it's base or it has a 1/8 inch hole in the base plate. If it don't have either, drill a 1/8 in hole in it's base plate. Some aftermarket thermostats didn't have either. Don't run it with no thermostat in it. Also look closely at the lower hose when you rev the engine quickly to see if you see signs of it contracting. Also it is a good idea to first run the engine with the radiator cap off and as you see the temp come up put a meat thermometer in the radiator and compare the readings with the gauge.
2. No the coil should not get very hot. It will get warm but not hot. It is usually written on the coil if it is suppose to be used with a ballast resister or not. A coil that requires a ballast resister when run without one will get so hot you can't touch it.
Let me know,
Howard
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QUESTION: Hello Howard,
I installed a 35 amp fuse, then jumpered the wires and the fans run - they are just a little squeally - they were like that before the rebuild - can they (or should they) be lubricated?
But the cooling system doesn't function right. The temp gauge goes up to hot and there is little change in the temp of the top hose to the radiator (from the thermostat) and even less on the bottom hose. Heater hoses do not get hot, fan blows cold air, and electric fans don't kick on. After I turn the engine off (when the temp gauge reads at the start of the red zone, all hoses get hot, fan blows warm air. So I think I have a full system without air pockets.
Prior to doing all of this I drained all coolant and refilled while I had the return hose to the engine from the heater split. After I filled the block and radiator I held the hose going to the engine up higher than the heater, and poured antifreeze in it until antifreeze came out of the other hose end of where I split and then put the hoses together with a brass connector and clamps. I feel this would have eliminated any air pockets while filling up the heater core. I checked the thermostat and it DOES have that jiggle valve in the base. I actually replaced the thermostat with another one I had lying around that I believe was good when I replaced it. The lower hose does not seem to show any contraction when engine is revved. The radiator does not have a cap. I fill through the thermostat housing.
The coil has not gotten hot either as I have been running the engine for testing. I could not find out for sure if it requires a ballast resistor. It is a Lucas Sport DLB105. From info I found, if it requires the ballast resistor it is another model - like 110 or something. I read somewhere that the coil could get hot while engine is idling from improper dwell angle setting. I don't have equipment to set timing and dwell, I was going to get that done along with a few other things when I take it for state inspection. It starts really easily - almost immediately. So I am not worrying about the coil for now.
But what about the cooling system? I don't know what else to try? I thought maybe the water pump?
ANSWER: I don't have a good test for a water pump but I have seen some mechanics claim the test they use is rough but effective. Temporarily remove the thermostat and drain your coolant into what ever you need to save it in. then fill the system with water and remove the upper hose from the radiator. (this needs to be done outside) hold the hose straight up and start the engine and rev the engine up. It only takes one rev up. The water should come out of the upper hose very fast. The contention is that if a water pump has broken off it's impeller or the impeller is spinning on the shaft the water will not come out of the hose. This is a rough test of the capabilities of the water pump to push coolant.
If it is good, replace the thermostat, drain the water out and put your antifreeze back in. A true test of a thermostat is to put it in a pan of water on the stove and use a meat thermometer to see that it opens all the way at within 10 deg. of the temp written on the thermostat.
Next run the engine until you have a temp on the gauge with the radiator cap off and a meat thermometer in the radiator and compare the gauge reading with the reading reading on a meat thermometer. This is a good test of the gauge.
Don't throw money at it until you have a target. The only way you can get a target is to test.
Let me know.
Howard
---------- FOLLOW-UP ----------
QUESTION: I performed the test you recommended for the water pump. Water came out fast when the engine was revved.
I tested the 2 thermostats in a pan of water with a thermometer. They both opened at around 18o F or 190 F which is right - they are rated 82 C which is 180.
I put it all back together with thermostat and antifreeze and it still runs the same - get to red zone and no electric fans. Upper radiator hose gets hot, lower and heater hoses not so hot.
I am not quite sure how to test the gauge, The radiator does not have a cap. Should I run the engine without the plug on top of the thermostat cover off, and attempt to get temp readings there?
Could a clogged hose to the expansion tank cause these problems?
Thanks.
ANSWER: Yes, that plug in the thermostat housing is a good place to check. But, first run the engine until you get at least a warm reading on the gauge and then remove the expansion tank cap to relieve the pressure and then remove the plug and put a meat thermometer in to get a reading and compare that with the gauge.
The electrical gauges are always suspect on over heating when the overflow is not spraying out steam and the fans have not kicked on.
Your test of the water pump and the thermostat are good so you can eliminate them.
Another test for a blown head gasket is to remove the expansion tank cap and fill the tank to the top and with the cap off start the engine. If you have a blown head gasket, the coolant will overflow the expansion very rapidly. (this is a preliminary test and if a car fails this test we would proceed with a combustion chamber pressure test using compressed air) If it fails this test let me know and I will detail how to run the test but you will need a air compressor to do the 100% test of the combustion chamber.
The upper hose should be hot to the touch and the lower hose should be warm but not quite as hot as the upper hose. You need to test the heater control valve to see if it is actually opening or not.
Yes a lower hose can have an inner lining separate and close up upon suction from the water pump.
You can check it but I have never seen an expansion tank hose clog up.
Let me know,
Howard
---------- FOLLOW-UP ----------
QUESTION: I removed the expansion tank cap, filled the tank, started the engine, and antifreeze did not overflow at all. I ran the engine about 30 seconds. Is that long enough? I hope that eliminates a blown head gasket problem - I just had the engine rebuilt.
Then I started the engine, got a warm reading (there are no marks on the gauge for temp, just a redline at the top of the scale). I removed the expansion tank cap (really wasn't any pressure to relieve), then removed the plug on the thermostat cover and inserted a meat thermometer. I never got to 180 on the thermometer, the gauge was redlined. I was afraid to keep running the engine. I suspect the thermostat was just starting to open.
I do know that the sending unit (screwed into the head below the thermostat) is new. The guy that rebuilt my engine broke the electrical connector off of the original. He got me a new one - the part came after I got the engine back, and I installed it. I have the box and it is a Standard TS233. I will try to find out if this in fact the right sending unit, but even if it is, is this what needs replaced?
Thanks.
AnswerGreat,I am comfortable that you have no blown head gasket. I am also sure you do not have an overheating problem as your gauge reading of redline at a 180 deg reading from the meat thermometer makes the gauge reading wrong. Add in the fact that the sending unit is a aftermarket sending unit I am sure you have a false gauge reading.
Before you condemn the sending unit unless you find they gave you the wrong part number. Check the voltage stabilizer mounted behind the Tach and by checking the voltage supplied to the gauge with everything connected to see that the voltage is less than 12v to the gauge. As I remember the reading should be around 10v TO the gauge. and a rough test of the gauge was to turn on the ignition and look at the gauge reading and remove the wire from the sending unit and read the gauge. It should deflect the needle in one direction all the way and then just momentarily touch the wire to ground on the engine and the needle should deflect all the way to the opposite end. That was a rough test we used in the dealership to see if a problem was gauge or sending unit.
I bet your sending unit is the wrong one. That is a guess so far but I feel that you car is ok and the hot reading is false.
Let me know.
Howard
