Heater core How do you replace the heater core in 1986 Chevy G30 van

There are only diagrams for the 1988 onwards to 1992 models. They don't show a headlight fuse either.

https://www.google.com/search?q=1986+chevy+g30+fuse+box+diagram

No relay either. It is puzzling.
https://www.rockauto.com/en/catalog/chevrolet,1986,g30,4.3l+262cid+v6,1047934,electrical

..

Look for smaller coolant lines coming off the back of the block or going into the firewall pretty sure it's in the dash

go on line to rock auto parts .com

Yes, I would say the thermostat is likely stuck open.

Charlie

I find this vacuum diagrams for 1986 Chevrolet Truck G30 1 ton Van 5.7L 4BL 8cyl (click over pic for zoom)...



Fig. 136: 1986 5.7L engine-Federal with automatic transmission (G10, 20 and 30 models)



Fig. 137: 1986 5.0L and 5.7L engines-California with automatic transmission (G10, 20 and 30 models)



Fig. 138: 1986 5.7L engine-Federal with manual transmission (G30 heavy duty models)



Fig. 139: 1986 5.7L engine-Federal with automatic transmission (G30 heavy duty models)



Fig. 140: 1986 5.7L engine-California with manual transmission (G30 heavy duty models)



Fig. 141: 1986 5.7L engine-California with automatic transmission G30 (heavy duty models)


Hope this helps; keep us updated.

If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.
When a heater core leaks, a new heater core is installed or the old one repaired.
Heater Housing

• The heater housing is usually under the dash and must be removed to gain access to the heater core.
• Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.

The heater housing is disassembled to get to the heater core. Heater Core

• Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
• Remove the heater coolant hoses.
• Remove the cable and/or vacuum control lines (if equipped).
• Remove the heater core securing brackets and/or clamps.
• Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
• To reinstall the heater core, reverse the removal steps.

When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.

Heres your wiring diagram it shows the complete heater wiring. hope this helps you,

Heater Core Removal & Installation To Remove:

1. Drain the engine coolant.
2. Release and reposition the outlet heater hose clamp at the heater core.
3. Remove the outlet heater hose from the heater core.
4. Release and reposition the inlet heater hose clamp at the heater core.
5. Remove the inlet heater hose from the heater core.
6. Remove the screws that retain the cover to the heater case assembly.
7. Remove the straps that retain the heater core to the heater case assembly.
8. Remove the heater core from the vehicle.

To Install:

1. Installation is the reverse of removal.
2. Refill the cooling system.

I believe on a 1987 chevy van the heater core should be under the black plastic cover on the firewall on the left hand side as you are standing in front of the van.
I believe you can also get to it under the passenger side dash.
It is NOT fun. Unless you are a seasoned mechanic, I would not attempt it.
Otherwise stop by your local auto center, and get a HAYNES manual, they will be able to show how to.

the problem is probably the heater core, it can become clogged with dribris. this stops heat from the engine getting to it and then no heat.