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Old 10-05-2009, 09:59 PM   #1
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Default Back again.. Help bypassing heater core

My 3.1l Lumina (amazingly, still running) has the 3100 V6 which I hope is similar to the 3800.. I was wondering how to go about bypassing the heater core in my car? I've tried to fix everything I possibly could, yet this car still overheats, all that'* left is heater core and head gasket. I figure if I could bypass the heater core then I could at least see if the car runs fine.

I know I have to connect the two hoses, I just want to know the best way to go about doing this. Or is it possible to just clamp the hoses shut on each end? I'm already running the car without a thermostat, and it still heats up, so I'm running out of options.

If anyone has instructions or tips on how to bypass the heater core, they'd be greatly appreciated. (don't worry about measurements of the hoses or anything, I can figure all that out)

p.*. Sorry about posting this in this forum, I didn't know exactly where to put it. I figured the heater cores would be similar in the two cars.
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Old 10-05-2009, 11:44 PM   #2
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Disconnect the inlet and outlet hoses from the heater core and buy a fitting at Home Depot to connect them together. What have you tried to fix the overheating?
  • change the thermostat (usually they fail open but sometimes they fail closed
  • flush the radiator
  • confirmed the water pump is pumping (I worked on a car once where the shaft was spinning free inside the impellor)
  • confirm your electric fan is coming on at the correct temperature
  • confirm the engine coolant temperature sensor is working
  • bleed the system
If it is the 3.1 v-6, the air in the cooling system has to be bled out. There are 2 bleed points, one on top of the water line for the heater (which is the black tube that comes out of the top just above the water pump) and the other is at the upper radiator hose inlet on the thermostat housing (some models have a silver tube from this one to the coolant tank. If it has the tube, you only need to bleed from the first point). The fittings are 7 mm and slotted screw. Get the engine warm with the cap off, and open the bleed screw(*) until all the air is vented. Then shut the engine off, top up the coolant and install the cap.

Do not assume the water pump is functioning just because it is not leaking.

Finally, drain some rad fluid and see if there is any evidence of oil in it. Are you losing fluid but not seeing any drips on the driveway? Do you have any whitish smoke coming out of the exhaust?
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Old 10-06-2009, 01:15 AM   #3
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^^couldn't have said it better! Just to add to your original inquiry, the 3.1 is a 60* v6 and the 3.8 is a 90* v6 so there is very little in common. I do know that the the older 3.1 MPFI'* seem to be more reliable than their offspring, the 3100, 3400, 3500 series... usually, they need new LIMG'* and you can buy an upgraded aluminum gasket. Also, if ur car has an oil pressure gauge, how is it reading?
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Old 10-06-2009, 09:24 AM   #4
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There is no smoke from the exhaust and no coolant in the oil, I check all the time.
Also, I have replaced:
Thermostat (twice, didn't work, now running with stuck-open thermostat)
Water Pump
Intake Manifold Gasket
Radiator Cap

I'm just going to try to get the hoses together and see if the car runs any better.

Also, there'* a problem with bleeding the system;
There is no bleeder screw (top broken off) above the water pump, so I can't loosen it. Also, there is an extra-large bolt in the second bleeder screw location, because the first one literally blew off somewhere in the engine compartment. I can loosen that one, but not the one above the water pump. Any other way to try to get the air out? I'm really trying to avoid taking it to a shop, I don't plan on paying much to fix this car, it'* either a cheap fix or it'* gone.
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Old 10-06-2009, 09:52 AM   #5
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I don't know if these are still available, but I used to be able to buy a radiator flush kit that consisted of a "T" fitting with a cap, and 2 clamps. You install it in-line into the hose feeding your heater core and hook it up to your garden hose. I used to run my car with the the garden hose on full and let the overflow come out the rad until it was clear. Then, drain 50% of your cooling system'* capacity from the rad and replace it with un-mized antifreeze. I don't know if the water pressure would drive air out of your system, and I don't know if draining your rad to add the antifreeze would trap air into your system.

Have you checked to see the fan is coming on at the right temp?
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Old 10-06-2009, 10:06 AM   #6
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It does come on, although not at the right temp.
What happens is, the car runs cool, then suddenly heats up quickly.
I guess it heats up so quickly that it takes a second for the fan to heat up.
When I say it heats up quickly, I mean I can watch the needle go from about 120 degrees to 260 in literally under thirty seconds.
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Old 10-06-2009, 10:26 AM   #7
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That sounds like a blockage to me. When you drained the rad for other fixes, was there any crappage in the fluid? I am also starting to wonder about your engine coolant temperature sensor.
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Old 10-06-2009, 10:40 AM   #8
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There is some crap that I can see in the radiator reservoir, I already knew that.

I also thought the temp sensor might be off, but the car has symptoms to go with the overheating.
Film on the windshield, bad smell when the fan'* on, rough idle when it gets really warm, boiling over reservoir, foggy windows with defoggers on warm.

I'm hoping that just bypassing the heater core will be a temporary fix.
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Old 10-06-2009, 10:58 AM   #9
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Aside from your overheating issue, foggy windows with the defogger on warm is the sign of a leaking heater core.

A faulty ECT can give you operating issues like rough idle. The ECU uses input from the ECT to adjust operating parameters for the engine.

Crap in the coolant and rapid changes in temp are signs of a blockage in the coolant system.

Are you the orignal owner of the car? If not, a lot of the symptoms you mention could come back to someone adding Bars Leak or something like that to the rad to stop leaks. If that is the case, you may be able to clear it with a good flush.

So far, we are narrowing this down to a leaking heater core, possible blockage in the cooling system, and/or a faulty ECT sensor.

Without physically seeing your car, I obviously can't tell for sure what is going on. I can only theorize based on what you are telling me. I think starting with bypassing the heater core is a good plan of action.
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Old 10-06-2009, 12:07 PM   #10
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Suppose I was going to just somehow connect the inlet and outlet of the two.
Where exactly is the heater core located? What would it look like inside the engine bay?
Where do the hoses go from the engine to the core, and back to the radiator?
I may just get a longer hose and connect it from the engine right to the radiator.
Either way, I need to know where the connections for the hoses are
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