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

118,955

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 of 2 people found this 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 of 1 people found this helpful.
118,955

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 of 2 people found this 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 of 1 people found this helpful.
118,955

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 of 1 people found this helpful.
75,685

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 of 1 people found this helpful.
65

Thanks for your input, guys. Really appreciated!

1 of 1 people found this helpful.
75,685

You're welcome. Glad to help. -Jim

1 of 1 people found this 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 of 2 people found this helpful.
118,955

That's great. Something simple.

1 of 1 people found this helpful.
75,685

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

1 of 1 people found this helpful.

Your Answer

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 61,758 nationwide Sierra 1500 listings starting at $1,295.

ZIP:

GMC Sierra 1500 Experts

  • #1
    dragonflyoffshore
    Reputation
    5,530
  • #2
    John Saffrahn
    Reputation
    3,820
  • #3
    Glenn Clingenpeel
    Reputation
    3,570
View All

Related Models For Sale

Used Ford F-150
2,998 Great Deals out of 230,655 listings starting at $1,300
Used Chevrolet Camaro
372 Great Deals out of 31,404 listings starting at $3,495
Used Ford Mustang
344 Great Deals out of 41,950 listings starting at $1,488

Used Cars For Sale

2018 GMC Sierra 1500 For Sale
9 Great Deals out of 29,959 listings starting at $22,639
2017 GMC Sierra 1500 For Sale
82 Great Deals out of 5,704 listings starting at $20,999
2016 GMC Sierra 1500 For Sale
115 Great Deals out of 3,467 listings starting at $14,500
2015 GMC Sierra 1500 For Sale
175 Great Deals out of 5,659 listings starting at $13,500
2014 GMC Sierra 1500 For Sale
187 Great Deals out of 4,257 listings starting at $9,995

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.