89, heat blows cold at idle

[MattStrike]

History: Last year I was having an issue with coolant disappearing on the '89 LeSabre. This obviously was causing the heater to not work. So this fall I ended up replacing the leaking LIM gaskets, water pump, thermostat, and a few other things to prep the car for winter duty.

Apparently, the leaking LIM gaskets were not the only leak. I can still smell coolant leaking under the hood after driving it. I don't see any witness of the leak, nothing in the oil which appears is also being consumed. The only other symptom is that at idle the air turns cold out the heater. As soon as you get on the throttle, heat come back full force, even after I just topped off and bled the system again. Which doesn't make sense to me because the servo uses vacuum to pull the airmix to hot, and is spring loaded return to cold; and at idle is when vacuum is the strongest. And it can't be a rotted water pump vane, because it's brand new.

So now I get to park it over some white paper to try and isolate where the leaks are. Unless it's a head gasket?

[RJolly87]

I would check the PCV system (bad/misplaced o-rings do funny things) for oil consumption, and take a close look at the coolant bypass system that I think runs under/behind the alternator. That leak can be fun to track down because it may leak intermittently.

[MattStrike]

I'm going to guess I have some sort of restriction in the heater core. One hose goes cold while idling and the other seems to stay hot.

[RJolly87]

If you have ruled out all possibilities of air being trapped in the cooling system, you may be correct. You know how them 3800's like to hold their air!

[96 SSEi]

IS the waterpump working well? I see it replaced - if the revs drop, the flow will drop, dropping vent temp. was the pump new and the correct part?

you can get a 4l bottle of CLR and fill to almost full of 50/50 in the core through the hose ( so the hoses to core are disconnected at the tensioner) and let it sit for about an hour or 2 - then get compressed air and put it in the hose and blow the core blockage free. works great for sediment, rust - repeat till you get good flow.

[Wes]

CLR soak works ok for the core, but what works best is to cycle it with a pond pump. I hooked up the Expy's cores to a pond pump in a bucket and let it cycle overnight. It was a world of difference vs just letting it sit. If you suspect a restriction in the core, that is about the best you can do short of replacing it.

[rustyroger]

The thermostat opening early or stuck open could also give you your poor heater symptoms. How cold is Michigan right now?.

Roger.

[Wes]

The thermostat opening early or stuck open could also give you your poor heater symptoms. How cold is Michigan right now?.

Roger.

Arctic circle cold.

[MattStrike]

Michigan is -6F right now. But that's not the issue, the lower radiator hose at idle is hot to the touch, it's only the heater core that's not playing nice. The infrared thermometer is indicating 185-195F at various points on the block (when I get home from work), and if I let it idle for more than 1 minute the fans turn on.

Interesting to note, the overflow was empty yesterday again, so I topped it off (while hot. I did try to pop the radiator cap slightly to check the level, knowing what can happen.. It was definitely under pressure and sent a healthy surge of coolant spraying). All day today the heat was working amazing, uncomfortably so, even at idle. The sun was out, so sunload wasn't helping. But not sure how the cooling system can hold that kind of pressure yet still have issues with cold air at idle.

And to answer any question about the water pump... Yes, it was the correct part. It's the less desirable stamped steel impeller design, for stupid reasons, but every 3800 ever has the same water pump. The cast impeller design is 'better', but I've had both designs on both my '86 LeSabre and my '89 Electra, the '93 SE and my fake racecar '93 SSEi both have the stamped impeller, and my '97 LeSabre and my truck have the cast impeller. Only my '89 LeSabre has had any issues, so I think I can rule out the water pump.

[MKMike]

The task is much faster and easier with a cooling system pressure tester.
Not only are you not burning yourself on hot engine parts and hoses but the escaping coolant won't evaporate when it sprays onto a cold engine or exhaust pipe.
Some parts stores lend them for free or you can buy your own from Rockauto or Amazon.
http://www.rockauto.com/en/tools/coolin ... ng+kit,249.
It appears that Gates manufactures the tool for Stant.
The tool is very easy to use.
The only caveat is to not exceed the pressure rating stamped on the radiator cap.

The heat issue is caused by the coolant leak. It keeps adding air to the cooling system.

[RJolly87]

Or air is already trapped, causing the issue. Next time it's hot and pressurized, crack the bleeder screw open on the thermostat housing until coolant comes out, and make sure the overflow has plenty in it. Keep doing this each trip until you consistently get only coolant. If trapped air is to blame, the coolant level should stabilize

[MKMike]

Or air is already trapped, causing the issue. Next time it's hot and pressurized, crack the bleeder screw open on the thermostat housing until coolant comes out, and make sure the overflow has plenty in it. Keep doing this each trip until you consistently get only coolant. If trapped air is to blame, the coolant level should stabilize

I would agree if not for the smell of coolant and the repeated, significant coolant loss.

In any case, I successfully eliminate the trapped air by doing the following:

First, I use the ACDelco OE thermostats which have a small hole pre-drilled.
There are thermostats that have no such hole, so drill a small 1/16" - 3/32" bleed hole in the very broad, flat part of the thermostat.

Here's the factory service manual cooling system bleeding procedure with my added step of opening the bleeder screw and squeezing the hose, then closing it prior to starting the car.


1)Open the bleeder valve.
Fill radiator to base of filler neck. I then squeeze the upper radiator hose a few times to help purge air out of the bleeder screw.
Wait 2 minutes, then add coolant, as needed.

2)Close the bleeder and install radiator cap with the arrows facing the coolant overflow reservoir tube.

3)Put heater and AC controls in any position except Max and set the temperature at the highest setting.

4)Start engine and allow to idle until the hose from radiator to water pump is hot.

5)Cycle engine speed up to 2500-3000 RPM and back down about 5 times.
Slowly open the bleed valve for approximately 15 seconds to expel any trapped air.

6)Close bleed valve and shut car off.
When cooled to ambient temps, ensure that both the reservoir and the radiator are at proper levels.