Expansion Tank

[poko]

I have a 1990 RRC with the white/opaque expansion tank, it has the coolant sensor in the cap combination. My question is: why would the coolant liquid be blowing out past the cap? Bad cap? I looked at it and cleaned it, seems to be okay. I don't have an overheating problem, the truck is running good, no evidence of water in the oil, what do you all think?

[kevin-ct]

Question?

Is the top radiator hose hard as a rock when the engine is running or is it soft?

If it's soft then it might be a bad cap. If it's hard as a rock, then you might have internal problems.

Normal, is a semi hard hose.

Let us know what you find.

[Terrys]

It may be that the cap is bad, but more likely you are over-pressurizing your cooling system because you have a head gasket leak allowing combustion pressures to escape into the cooling system. The most obvious symptom to check is if the top hose is hard as a rock after running at speed for a short duration. If this is the case, either go to a service station that has an exhaust gas anylizer and have them 'sniff' the cooling system (either at the top radiator plug, or expansion tank) for hydrocarbon levels higher than 12-15 ppm,or, get a "Block Test Kit" from Carquest, or NAPA, and do it yourself. The kit consists of a vial, filled with a chemical which will change color when Hydrocarbons levels are presesnt, when you draw air through the vial with a vacuum sueeze bulb.
If the tests confirm the presence of exhaust gasses, you'll have to pull the heads at a minimum, and change the gaskets. While the heads are off, have the heads crack checked, as it isn't rare to find a crack in the exhaust valve pocket, which will allow gases to escape into the cooling system. The last reason, is the all too overpopularized cylinder liner issues, though these are far more rare than the urban legends would have you believe.

[poko]

The top hose is not hard. I'll get the block test kit today and check it out, thanks.

[kevin-ct]

If you live in lower Ct you can use mine.