OT GM fullsize with no heat

[Young Ed]

I know a few of you had some knowledge of these things before so hopefully someone will chime in again. Car is a 97 bonneville. Besides its other issues the heat has stopped working. Now its not my car so my friend brings it over and leaves it for me to look at. I get in to move it and the heat is fine. So I drive it to work this morning and the heat is gone again. Fan blows fine its just cold air. I gotta think with the heat I had yesterday the heater core is good. What else to check?

[Plymouthy Adams]

air lock...I have been know to fix these by hand filling the heater hoses..else it could be a directional style thermostat that was recently replaced in incorrect possition..some cars are this way..this model I do not know about...check the shop manual or online forum...

The air lock I know sounds funky but with a lot of cars today...the heater inlet is so much higher than the engine...

[Young Ed]

I've got a worry that this thing needs the intake plenum that goes on EVERY 3.8L GM car. My moms car needed one at about 50K. This thing has 140K. Might needs its second one already. I think a couple times its been low on water and been filled back up. That could perhaps explain an airlock.

[greg g]

By pass the heater temp valve. If you have heat with the valve bypassed, its probably the valve, many of these were vacuum operated and the diaphram or the vacuum line might be suspect, leaving the valve in the closed position. See if the hose to the valve is hot. If not could be the problem that Tim mentioned.

[Young Ed]

Greg Any ideas where to look for this valve? I didn't look at it much last night as the heat started working but I couldn't even find the heater hoses last night! Lots of stuff under there

[Young Ed]

Well after a little research on the net I found this. Sounds like a likely culprit and not a fun fix.

http://www.bonnevilleclub.com/forum/viewtopic.php?t=15360&highlight=

[1just4don]

TOTALLY unfamiliar with this car BUT here is what a friend told me the other day when his granddaughters acted strange. His granddaughter would drive someplace(close, not like 100 miles away) like to school and back 3-4 miles. It got hot and boiled water out the radiator something fierce.(Every day this was happening) he took it to a fix it place where he gets his work done and they ran all pertinent diagnoses,,,turns out to be a BAD radiator cap. He was mad as a wet hen when he got the bill for 100 dollar radiator cap. They said to prevent it furthermore,,, to replace them every year needed or NOT!!!

Not to say that is exact prob of your car BUT if its low on water/antifreexe, then heater dont work causes maybe thermostat to overheat and warp, stick etc. OR like been said maybe the water control valve.

BYW I see LOTS of people who just fill there overflow jug when the radiator gets low,,,thinking thats all they have to do when it wont suck it in there and still gets hot,,,BUT some of those cars didnt even have a radiator cap on them,,,how those fill the radiator from say an all empty condition,,,I will never know!!

[Plymouthy Adams]

trust me they work..I do not have a radiator cap on the radiator of 4 cars I own..they are remote located about 4 feet away on the reservoir itself..

When servicing these...I do two things...first is drill a small hole in the thermostat flange to air bleed the block...when filling I have a bleeder ahead of the hole that I open...I fill the reservoir, start engine, keep rreservoir at good level till I see a steady stream of water fromt he bleed port..shut off port (similar to brake bleeder) and drive..

If you have a vacuum ported hot water valve and you suspect it..there should be a lever in view that you can hand operate and wire in this position while testing the flow...

On my Chrylser with AutoTemp..there is a calibration procedure..this will drive all doors and servos to full open and close extention/retraction...and will calibrate the unit...takes about 3 minutes to run...if errors in the device and unable to calibrate..will display a fault code...but of course..this is a Chrysler...

[Ed Griffin]

I've got a worry that this thing needs the intake plenum that goes on EVERY 3.8L GM car. My moms car needed one at about 50K. This thing has 140K. Might needs its second one already. I think a couple times its been low on water and been filled back up. That could perhaps explain an airlock.

You may already know this but as with any leak like the one mentioned above it can be found by spraying wd40, etc. around the plenum to see if you have an actual leak with it. Also as you prob. know it will rise in rpm's if you find the leak. Went through this on a 95 Riviera but there was no heat problem. Erratic idle and loss of power but no heat problem. Dont you just love those new hard plastic gaskets they make for those?

Sounds as though you got some good ideas on where to look for the heat issue.

[Paul Beard]

Have you checked for a bleeder valve near the thermostat. I had a 2000 Bonneville that I was told most newer cars all have to have the air bled out of cooling system or they would not put out any heat.

[Young Ed]

The heat does work sometimes and then not others so I've kinda ruled out the airlocked thing. Seems that would be permanent or would stay gone once gone. Radiator is full and I was happy to see good old green antifreeze in there.