SLO dave

My sister-in-law has a 1991 4 cyl. 4wd pickup with the following symptoms:

1.starts normally.
2.after idling approx. 2 minutes the idle starts to lope.
3.as it lopes, the exhaust sounds like a "chug" as if a cylinder is missing.
4.at the same time you can begin to hear an air surge come out from the coolant reservoir breather.
5. if the truck is run for a long time (she had driven for 25 minutes when she first noticed this) the coolant boils and is vents out of the breather, all over the left wheelwell.
6. i checked the thermostat and the rubber gasket and seal were gummy and damaged from heat so i changed it.

i know it sounds like a bad valve/head/cylinder, but why would it take two minutes to show? plus, there is an audible "click" and change of idle speed very shortly before the loping starts (emissons control/vacume, etc.). any suggestions other than the worst case scenario of a bad valve/head/cylinder?

ekim121

I just changed the head gasket on my 22re and it had many of the same problems. It was loping at idle, was venting out of the coolant overflow, and the thermostat was all gummed up from excessive heat. The problem with mine was that the head gasket had gone bad and coolant was leaking into one of the cylinders where it was being burned. In return, exhaust gasses were getting into the cooling system and thus venting out the overflow. Hope that info helps.