The vehicle owner never catches damage to the heater core nearly 100 percent of the time before it actually happens. Unlike other engine components, the heater core on the S15 sits quietly tucked away under the dashboard until theres a problem with it. The sweet smell of sugar inside of your truck definitely isnt that new air freshener. The heater core has ruptured and that smell is coolant leaking all over the passenger-side floor area. Replacing the heater core on your 1990 GMC S15 can be done right at home with a few simple tools. The repair should take you 40 minutes or less even if its your first attempt at auto repair.
Instructions
- 1
Raise the hood on your S15 and remove the radiator cap. Position a coolant drain pan under the trucks radiator in-line with the coolant drain cock. Open the drain cock and allow half of the coolant to drain, and then close the drain cock. While the coolant's draining, instead of looking down into the radiator to see when you have reached the halfway point of coolant in the radiator, count to 45 and then close the drain cock.
2Loosen the retaining clamps on the heater core hoses at the firewall with a flat-head screwdriver. Then pull the retaining clamps back on the hoses approximately six inches. If your heater core hoses have spring-tension clamps, use a pair of pliers to squeeze the clamp tabs together to move them back on the hoses.
3Pull both of the heater core hoses off the inner and outer heater core tubes. Position the hoses so theyre pointed upward to avoid the bit of coolant still in them from spilling.
4Open the passenger door and identify the heater core housing cover beneath the dashboard at the firewall. The cover is black and shaped like an odd rectangle.
5Remove the five bolts from the heater core cover with a socket wrench. Do not misplace the bolts; place them in the cup holder and then remove the cover from its position.
6Remove the bottom bolt on the left and the one on the right securing the metal retaining straps on the heater core. Slowly and carefully, bend each of the straps upward away from the heater core. Each strap also has a bolt at the top of them. You do not have to remove their top bolts, but if you feel more comfortable doing so rather than bending the straps, do so.
7Remove the heater core by pulling it toward you two inches and then lower it from under the dashboard. The heater core still has coolant inside of it. Be careful so you dont spill any more coolant in the truck. Install the new heater core by completely reversing the removal process exactly. Use a funnel to refill your radiator with the coolant in the drain pan.
