Since the members of this club are some of the best gearheads on the planet, maybe you can help a brother out.

I have a 98 Aurora with 104,000 with the 4.0 "little Northstar". Several weeks back, it started to have cooling problems. After about 10-15 minutes of driving, the heat would quite suddenly go cold, then the coolant temp would climb to anywhere between 225 to 255ish. I have flushed the coolant, changed the t-stat twice, pulled and inspected the water pump, replaced the coolant cap, and examined all the spark plugs. Nothing.

I would assume it was a head problem, but for this: on a couple occasions when I was driving it and the above crap happened, before I could get to where I was going, just as suddenly, the heat would get hot again, and the engine temp would fall back down to 210-225 and stay there for a while, then 5 minutes later, no heat, temp would rise a little again, but only to about 230-ish, stay there and no heat. All this would happen on a trip home from the office, which means I'm moving 95% of the time, anywhere from 40-70mph.

I have driven the car probably 10 times since this started happening, and every time it will do most or all of the above like freaking clock work. With the problem coming and going like it does, it seems like it couldn't be a head problem, but I don't know what the heck else to look at now?

Ideas?

You might want to try and get ahold of Clayton. I think he drives an Aurora.

QUOTE (Headrage @ May 2 2005, 12:14 PM)

You might want to try and get ahold of Clayton. I think he drives an Aurora.

yup. twystd1 has an oldsmobubble...

Sudden temp swings back and forth means you are getting air around the temp sender.

Pressure test your cooling system - hopefully you have a small leak that you just don't see rather than a blown head gasket...

QUOTE (James Adams @ May 2 2005, 01:22 PM)

Sudden temp swings back and forth means you are getting air around the temp sender.

Thanks James. THATS what I'm talkin' 'bout with this crew.

I had considered something like that too, but then why does the heat go from hot to cold? Coolant flow has got to be stopping somehow, doesn't it? Could air be causing the flow into the heater core to stagnate?

Also check that the sender is operating properly. May be due for a new one. It's used for various engine management functions one of which may involve heater control. Also check operation of your cooling fans whether electric or belt driven, and kinking of radiator hoses.

QUOTE (914GT @ May 2 2005, 01:32 PM)

Also check that the sender is operating properly. May be due for a new one. It's used for various engine management functions one of which may involve heater control.  Also check operation of your cooling fans whether electric or belt driven, and kinking of radiator hoses.

hmmm,

Fans are functioning properly, but it does have the "hey-wow" thermostat controlled heat, with temp and blower automatically controlled based on whether the engine is warm yet. My buddy Stef has All-Data at his shop (monthly updated CD collection of shop manuals for literally any car newer than 1983), and the troubleshooting flow chart for overheating doesn't mention any steps related to senders, which I though was odd given how many things on the climate control are automatic. Maybe I better have a look at the troubleshooter for climate control.