denverdog

"93 ls400 with 247,000 miles. heater is just barely heating the air until out on road at 50 mph or more for a couple minutes, then heats up fine. as soon as you get to a red light, it cuts immediately back down to barely heating the air. as soon as you get up to speed, its fine again. no smells or leaks noticed. the cooling system seems to work fine; no fluctuation in the engine temperature. not running low on fluid. can't seem to find this problem in my searches. heater fan works fine, and flow changes appropriately with the buttons. any help?

acidfire52

You have air in your cooling system. Check out lexls.com tutorials about how to bleep it.

randal

I would agree with there being an air pocket in your system. That is the most likely issue especially if you recently changed coolant or refilled a low sytem (did you?).
However, there are other possible contributors. One being low coolant flow through the heater core because of a barely open heater valve. Or clogged heater hose. But an air pocket is the leading candidate at this point. You might want to replace the reservoir cap to ensure proper pressure on the system. Lots of threads on this subject.

deanshark

I would also have to say air in the system. Last week I posted, in a different thread, I had same symptoms after I changed my heater core. I bled mine and it seemed better, BUT, I can't tell ya if it fully worked b/c the car died a day later. Total different problem, not related to the heater core.

denverdog

i'm about due for a cooling system flush, so i'll see if that does it.

ntrsssgti8

is it actually the heat that goes away or does the fan slow down when you idle down?
my fan slows way down when the engine idles down to 400 rpm were it idles but that is alternator related or a drain in the system that the alternator can't power at idle.

V.I.P LS4

did you ever change your thermostat

oldskewel

iTrader: (1)

This question ^^^ really needs to be answered first. If the fan speed does not change, but the temp of the air coming out of the vents drops suddenly, yes, that probably points to air in the coolant. But if the fan stops, then it could be an electrical issue.

My '91 is similar to the one mentioned in the quote - when coming to a stop, the fan speed instantly slows, and then instantly picks up as soon as my foot hits the gas to start. I would guess this is a programmed electrical switch rather than just a drop in speed with reduced alternator output voltage. Anyone have more details on this feature?

denverdog

the fan is unaffected. the thermostat was changed about 5 years ago. this problem just started hapening about a month ago.

billydpowe

iTrader: (1)

replace your thermostat and be SURE to get ALL the air out and you will have a working heater (I hope) (core could be blocked, but not likely)

deanshark

Like ya said "not likely" about the heater core being blocked. If it was there would be NO heat at all. 99% it's just air.

onyx10

How does one bleed the system? I'm having the exact same issue...also do these cars take longer to warm up over time or is that just another symptom of air in the system?

deanshark

There is a 17mm bolt ontop of the thermostat housing you can loosen while the car is running to let the air out. Pic 5 of this http://www.lexls.com/tutorials/cooling/coolant.html shows the bolt out, don't take it all the way out or coolant WILL flow everywhere.

randal

Depends on the year. 97 on down use the 17mm bolt, 98-00 use a 10mm hex bolt. You may not even have to mess with the bolt to bleed the air. The easiest way is to raise the front of the vehicle a foot or so. You could use ramps, jack or even park on a hill. This gets the radiator top (where it transfers to the reservoir) higher than the heater core for more effective purging.

deanshark

First words in the first post, "93 ls400 with 247,000 miles". I usually jack it up, just to have it that much higher, and loosen the 17mm bolt till I don't see any more bubbles come out. Then, it's good to go. I always used to get air in mine b/c of a leaking heater core. (fixed)