1990 GMC Sierra idling rough and guzzling coolant. Why?

65

Asked by Jan 03, 2015 at 10:20 PM about the 1990 GMC Sierra 1500

Question type: Maintenance & Repair

Truck has started idling really rough when, say, stopped at a light. The idle continues to
be rough when I pick up speed, but it tends to even out a little. On top of that, my coolant
has been disappearing a matter of hours after filling it up. Even though  coolant seems to
be disappearing, I haven't yet overheated, so I'm assuming that is one positive about my
situation.
Any ideas?

11 Answers

101,415

Do you see where it is leaking from? No sign of a leak? Check oil. Does is look like a milkshake? Any white smoke out exhaust? If can't locate where coolant is going you might have a blown head gasket.

2 out of 2 people think this is helpful.
65

Oh wow, ok. So I topped up on oil about 250-300km ago, and my dipstick is showing nothing. To clarify with my coolant, I noticed it had sprayed all over my motor and pretty much everywhere underneath the hood. Didn't notice anything off about the exhaust at all.

1 out of 1 people think this is helpful.
101,415

Might want to do a pressure test on your cooling system. This will show you where the coolant is going. If you notice a drop in the pressure gauge but not seeing any leaks remove the spark plugs and see if coolant is on them.

2 out of 2 people think this is helpful.
65

Will do, thank you for your help! I was hoping it might be something more simple like a water pump or spark plug issue alone, but if guess it's not sounding quite like that.

1 out of 1 people think this is helpful.
101,415

Might be something simple. Like the coolant is spraying on something that's just not liking to be wet. When leak is repaired the other issues might take care of themselves.

1 out of 1 people think this is helpful.
56,655

Exactly, if the ignition system (distributor cap, or spark plug wires) is getting wet from the coolant leak that'll definitely cause a poorly running engine. HTH. -Jim

1 out of 1 people think this is helpful.
65

Thanks for your input, guys. Really appreciated!

1 out of 1 people think this is helpful.
56,655

You're welcome. Glad to help. -Jim

1 out of 1 people think this is helpful.
65

Thanks again guys! Found out I actually have a small hole in my radiator, and I need to replace one spark plug wire!

2 out of 2 people think this is helpful.
101,415

That's great. Something simple.

1 out of 1 people think this is helpful.
56,655

Glad to hear that! You're welcome. Glad to help. -Jim

1 out of 1 people think this is helpful.

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