Thread: 2003 Gr Prix Heater Problem and other issues.

Originally Posted by kennn

2003 Grand Prix GT 3800 Series II Automatic

Heater Issues

Car doesn't heat or at times doesn't heat well. Going from my recollection of last year: depending on outside temp, heater would heat moderately when driving at high speeds, luke warm with continuous driving and cold as soon as the gas pedal released.

Heater inlet hose (lower) is hot after the car had warmed up (185 per temp gauge)

Initially heater outlet hose seemed cool even after the car had warmed up but eventually did warm up albeit at lower temp than inlet hose.

Air flow from heating unit significantly reduced when heater switch turned from cool to hot.

With the car idling and temp set on cool, and then turning from cool to heat, the car blows moderately warm air for thirty seconds or so and then cools with no significant heat.

When reversing the thermostat from heat to cool the temp gauge increases slightly to 4-7 degrees.

When engine was raced, air flow got warm for a short period of time and then cooled down

Other issues

1. Bottom of radiator cap and inside the fill port had small globs of gunk. Filled radiator last year and bled air out of system form top of engine, now requires refilling although surplus reservoir is approximately 1/3 to 1/2 full. Last year may have topped off with Preston AF Advancd Forumula for all metals (i think), wasn't aware that (maybe ???) you were suppose to put something else in it like Dexcool??? come to find out Dexcool appears to be very controversial and unsure if I should clean the system and replace with something else

2. Reved up the car to get the heater hot and engine rpms met abrupt resistance at 44K rpms, Beyond this point the engine seemed to struggle and car body shook. That was strange.

Any thoughts, resolutions and/or recommendations appreciated

you might want to put in a new thermostat. you can use dex-cool, but you have to change it every 3 years or at 50k miles. under no circumstance leave it in for 5 years or 150k like GM say's. you,re asking for trouble. you can also use a universal coolant as well. that's what i use.
it sound's like your thermostat is probably stuck open. have you put in a new lower intake manifold gasket yet. those engines eat them up after about 100k miles.

Originally Posted by gpbastard

you might want to put in a new thermostat. you can use dex-cool, but you have to change it every 3 years or at 50k miles. under no circumstance leave it in for 5 years or 150k like GM say's. you,re asking for trouble. you can also use a universal coolant as well. that's what i use.
it sound's like your thermostat is probably stuck open. have you put in a new lower intake manifold gasket yet. those engines eat them up after about 100k miles.

your post was a bit cryptic but are you losing coolant?