QuestionMy 1970 MGB GT overheats. When it starts up the oil pressure reads about 10-15 at idle, picks up a little when driving then drops to almost nothing. After about 2 miles the car misses/loses a lot of power and then the temperature begins to climb. How can I begin to troubleshoot with symptoms pointing in different directions?
AnswerHi Ted,
I thought i answered this one but it is showing up as still pending so here it is again.
Low oil pressure is an indication of a bearing problem but to be sure you should connect a known good hydraulic gauge to the engine. connection is at the right rear side of the block next to the rear oil cooler line. First be sure the oil is not contaminated with fuel (very thin) The pressure at idle should be 25 to 35 PSI and at 3000 RPM it should be 50 to 80 PSI. If you have good oil pressure at high RPM but very low pressure at idle check the pressure regulator valve in the side of the block to see that it is seating and the spring is good. MGs rarely ever have oil pump problems. The only other thing is to pull the pan and see that the pump pick-up screen is not clogged due to the lack of oil changes.
As far as overheating, the most common is a leaking head gasket. The easiest test is to get dye that you put in the cooling system to test for CO. (available at most auto parts stores)
A 100% sure test is to get a fitting to adapt an air hose (if you have air available) to the spark plug hole.
Place the piston at TDC of the compression stroke, put the hand brake on hard and shift lever in 4th gear and apply air pressure to the combustion chamber. Remove the coolant cap and watch the coolant level. If there is even the slightest leak the level will raise.
(This is also a 100% test of both valves by listening at the carbs and at the tail pipe for a hissing sound. The slightest leak will hiss)
If there is no CO in the coolant then you could have a bad thermostat, partial stopped up radiator, loose impeller on the water pump, collapsing lower hose or fans not operating.
let me know,
Howard
