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Joel, GM Dealer Technician
Category: Pontiac
Satisfied Customers: 1603
Experience:  18 years plus at same GM dealer.
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Pontiac Montana: 2004 Pontiac Montana: original problem was

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2004 Pontiac Montana: original problem was heat would go to luke warm when idiling, and fine while driving. it would be low on coolant. i'd fill it up and would be fine.

took it in to find out why it was going low on coolant, and ended up being intake manifold gasket. they replace that along with thermostat and heater core. got it back and no heat to front of van at all, fine in the rear. 7-10 days later after no heat to front of van, now every once in awhile the front heat will be fine, then on the way home from running errands, again back to barely even warm air blowing. it seems like the air is warmer on lower fan speeds when it does work, and turning the fan up higher turns it to colder air blowing out. the couple of times the front heat did work, it was like the original problem of low heat when idiling at a red light and fine when you are driving. i need diagnostic help to rely to the shop that is literary leaving me in the cold help so i can get my wife heat taking our kids to and from school

Hello and welcome.

It does sound like you are still getting air in the cooling system. The problem of no or little heat at idle is a result of air pockets. When the engine is at a higher RPM, more coolant is flowing, so more heat.

The low coolant because of a leaking intake manifold gasket is a VERY common problem, but sometimes the shop overlooks the fact that there may be additional problems, namely- the rear head gasket.

When they fail, it give the exact problem you are talking about.

Joel and 3 other Pontiac Specialists are ready to help you
Customer: replied 4 years ago.

so why is the heat to the rear fine?

For some reason the air pockets never make it back to the rear heater core. I believe it has to do with the way the hoses are run, the air always gets into the front core.

You may be able to see air bubbles in the coolant with the cap off and running at idle. Removing the passenger side rear spark plug may show signs of burning coolant.