That depends on your model and year. Older rigs definately have a valve to open flow to the heater core. newer rigs with climate control have full flow. Not sure on diesels or newer base models though.
It is a 93 LWB 4.2 v8, know offhand? I can't seem to find any indication of a valve in the shop manual coolant section.
Ahh I found this sentence in the shop manual: As water is circulated through the radiator continuously, selection of hot or cold air achieved by the operation of air flaps which direct the air flow through the unit.
This explains the recommendations to replace the HC as a preventative measure as there really isn't a very easy way to bypass it. Any idea what the life expectancy of the heater core is in a 93? I am a little wary of mine being that I just replaced the radiator due to a leak... I'm considering do the HC as well but not looking forward to disassembling the dash and heating unit.
When I bought my 1993 LWB over a year ago the heater core had been bypassed. I assume it gave up the ghost and leaked all over the passenger side floor. When they go it can be a mess.
I have not replaced mine as is does not usually get very cold in south Texas in the winter. However, there were quite a few days last year that I really could have used it. I had planned to replace this fall. I just am not very excited about taking the dash apart and putting it back together. I still have the rear airbags to replace and a renewal of the EAS valve system to do and I figure that is more important since it really doesn't get cold here until January/February.
I would recommend when replacing your radiator to replace all of your hoses as well.
Thanks Parker, I did do all the hoses and radiator the only "weak points" left that weren't done are the water pump, head gasket, and heater core. Pressure tested and all was OK, a few days later developed a little leak from what appears to be the water pump gasket (definitely coming from the the vicinity of the water pump). Just a few drops I see every once in a while that have fallen down past the belts and onto the trans cooler lines, looking up with a flashlight I can see droplets on one of the "brackets" connected to the water pump near the very bottom corner of it (right side if looking at engine from front). The pump was done as a DIY job by the previous owner about 4 yrs / 12k miles ago, I am thinking he didn't torque it down enough or didn't seal the gasket or it looks like he re-used the bolts so maybe that is the reason.
I'm fatigued by repairs so I'm just going to monitor the situation and take action if it gets worse. So far the heater core hasn't shown any signs of weakness but who knows. I think I am just going to wait and see how many miles I can get out of it. I'll update you all when it blows!
Did you replace the small hoses near the distributor. The small hoses in that location can leak and make it appear that it is coming from the water pump area. I would get the truck up to temp, keep it running and pop the hood and take a look and listen for small pin hole leaks. Turn it off and do the same. You may be suprised where the leak is coming from. And it could be a easy fix.
As far as the heater core is concerned. I would keep a length of heater hose in the truck with some clamps so that if it goes you can cut the hoses on top of the engine and put the bypass on the inlet to heater core and outlet from the heater core. Maybe about a foot and a half of hose , make a loop and a few clamps to clamp it down. If you don't bypass coolant will keep coming in through the leak in your heater core on to your pretty carpet.