Question about 1999 GMC Jimmy

1 Answer

1999 Gmc Jimmy water leak under the transmission

I found a leak of antifreeze under my truck (99 Jimmy). I thought it was my heater core but a friend of mine told me that if the heater core goes bad, it leaks in the inside of the truck. He told me it may be a hose, and he explained to me that as the car get hotter the leak get bigger (Which its true). My problem is that I can't find the leaking hose. The leak is located right above the transmission and leaks right under the driverside. Now I have followed the two main hoses that go to the transmission from the radiator, but they are connected under the passenger side, left side of the transmission. I have tried to use a mirror and a flashlight to look for the leak above the transmission, but I am not getting it. Am I going have to start taking parts out from under the vehicle to get a better view or am I going have to take the dash out? I am trying to do as much as I can to learn how to fix my truck. Do you think you can help me? I just don't know where to start. Thanks.

Posted by on

1 Answer

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Expert
  • 161 Answers

I believe the heater hoses are on the pass side on your truck, but have you checked where the heater hoses go into the truck? Otherwise on the driver side I would check 2 things after I checked the hoses 1. Intake manifold check it up and down they are bad for leaking at one of the corners. and it could be running down the back onto the ground. 2. check the freeze plugs. if you can go to autozone see if they will loan you a coolant press test kit other wise they are about 30$ for one .With the car off top the coolant off and press the system to what the rad cap is rated 15 or 16 ect. get your flash light and chase the drip. I would say the intake is your first shot at finding it. if you have a uv light you can also add dye to the system let it run and find it. First get some thing to stand on get on over the intake and find the coolant just remember it can leak from here and run and drop there. hoses , intake , freeze plugs

Posted on May 25, 2009

Testimonial: "Thanks! This information really help. I know its a little late but thank you so much. I did follow the leak and it was the head gasket. "

1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

4 Answers

Why would my 99 Yukon have antifreeze blow back in rear of truck

What do you mean "antifreeze is blowing in the back of the truck", that is not clear at all.

Feb 09, 2015 | 1999 GMC Yukon

1 Answer

How bad is it if the antifreeze is leaking through the floor of a 1991 gmc jimmy?

Your heater core is leaking.....Antifreeze is used to prevent rust in engine block among keeping water from freezing.... YOUR Engine will get hot and at one point it going to lock up on you because it got over heated... you can bypass core if you want to...

Sep 10, 2012 | Cars & Trucks

3 Answers

We just bought a 1999 GMC Jimmy and the heater doesn't work. The fan blows but there is no heat. The air conditioner works fine.

Could be that the heater core is disconnected, there are two hoses that attach to the heather core that come out of the engine, this provides hot water to the core thus making the heater work, when the heater core starts leaking water the quick and fast fix would be to bypass the heater core and connect the two hoses together, check under the hood on the left passenger side there should be two hoses about 1" thick see if there are connected together or of they seem to be connected to 2 outlets that come out of the inside of the vehicle. people do that specially if selling vehicle.

Sep 06, 2010 | 1999 GMC Jimmy

1 Answer

A/c blowing hot air and leaking antifreeze/coolant from heater duct. How do I locate problem?

Your heater core is out or you could have a leaky hose that connects to your heater core. Pain in the **** to get too but not too expensive.

Jul 20, 2010 | 1999 GMC Jimmy

1 Answer

I have a 99 jeep grand cherokee with water flowing from a what looks like a drain from the heater core area. the floor isnt wet and the heater works could the heat core have a crack

Is water coming out or is it antifreeze? If its antifreeze you have a heater core leaking. If its water than it's normal. The air conditioner is also a dehumidifier, and that is where the condensation comes out.

Jul 01, 2010 | 1999 Jeep Grand Cherokee

2 Answers

Wet floor on passenger side under carpet

Wet with water or wet with anti freeze? If its water, it could be from the a/c evaporator drain stopped up, if its antifreeze its from a heater core leaking.

Dec 15, 2009 | 2001 GMC Jimmy

2 Answers

Can i still drive my 99 dodge durango with a bad heater core?

well if the heater core is leaking then your coolant is leaking as well, heater cores leak on the inside of your car so your car will get water damage and will smell like antifreeze, so i wouldnt drive it

Sep 28, 2009 | 1999 Dodge Durango

1 Answer

Smelling antifreeze inside cab of 2000 gmc jimmy

Chanses are that little hole will turn into a big hole its only a matter of time, its not that hard, don't be inteminated by it, even if you have never done one before. Chk. the carpet on the pasengers side floor see if its wet, anyhow if you can smell antifreeze thats what it is heater core.

Jul 31, 2009 | 2000 GMC Jimmy

1 Answer

Antifreeze leak 1996 gmc jimmy 4.3

sounds like it may be coming from your heater core or one of the hoses that run to it to be leaking in that area

Jan 18, 2009 | 1999 GMC Jimmy

Not finding what you are looking for?
1999 GMC Jimmy Logo

451 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

75797 Answers


Level 3 Expert

1311 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22114 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides