from previous post:
Crazy..My dash gauge will show the temps going all the way up to 240* or so within 2 min of me starting the car from a cold start. Then it starts fluctuating up and down and within a minute it sometimes goes back down to 150*. Meanwhile my DFI temp guage (laptop) is pretty steady between 160 and 180 (back and forth) which would make sense because that's how I have the fans set. While my dash guage is showing 240*, I open the hood and feel the radiator, It's barely even warm and no overflow in the tank. Are these two gauges running off different sensors? Where is the sensor located for the dash guage? Where does the DFI pull it's data from??? Thanks!

Decided to try burping again....

I checked the overflow and it was at correct cold level. undid rad cap and started car. let it warm up and raised rpms to 2K level went down and kept filling...and filling...and put in 3/4 gal of fluid until to top of fill area. Put cap on turned off car. started up and it was much cooler. Took it for a cruise..never got above 170*. Came back shut it down. started up again and let it idle...went up to 220* and stayed there. WTF?? Could my t-stat be F'd? I think my guage temp sensor is ok now. When I turned the car off, I hear air escaping from the cap. Is that normal? Sorry for long post.

 

"When I turned the car off, I hear air escaping from the cap."
Not to my knowledge is that normal. Otherwise, you don't have sufficient pressure in the system. At very least, sounds like a new cap is needed. That doesn't solve the fluctuating temps tho. And something's off if it's up at 220 w/in 2 minutes (I know, master of the obvious...).

 

Would an air pocket in the head cause this? If the head is not getting any coolant for some reason, is that the temp the sensor would show? Again, the ECM coolant temp was normal. When I got the Guage temp down to 160 or so, it matched perfectly with the ECM temp.

 

Already you're starting off better than yesterday.Remember how a thermostat works and what it does. Ir cannot control how hot the engine will run, only how cool it can run. Not exceeding 170°, driving down the road, makes me think your stat may be stuck open. It SHOULD run hotter than that. The 220° you saw, sitting still and idling is really NOT a problem. I suspect the air you heard escaping from the radiator cap was excess pressure (over 15#) as the engine heat soaked. It should have been water going to the overflow tank not air, but I believe you hadn't finished "burping" the engine yet.

I think that is a pretty good indication that I wasn't TOO far off, yesterday.

Check your stat, and continue burping. After I burp mine, as you did yours, I like to keep pulling the rad cap after it cools after each warm up, and see if I can squeeze any more coolant into it. Like tightening header bolts, you will soon realize when it is no longer necessary.

RACE ON!!!

 

Try inclining the front end-and burp again.

 

Thanks all. I will keep burping it. I just don't understand why while driving steady on the highway, the temp is fine for 10 minutes and all of the sudden I look down and it starts moving up 1 degree a second until it hits 220+ or so? Would an air pocket cause this?

 

Dave,

The dash is pulling your temp from the sensor in the front of your manifold, down low and in the front. Just below the one water outlet that runs to the heater core.

The ECM pulls the temp from the one sensor on the side of your head.

Now the way your system is wired up, it might be reversed, but these are the two locations.

When I drove your car it stayed VERY cool, remember me commenting on it. Even the radiator stayed cool, but you have that large aftermarket radiator so I don't think that is a big issue.

As for getting all the air out of your system, the easiest way to do this and what I always did with no problem, is get the car start and let it idle with the rad cap off. Eventually when the temp hits about 160-170, you will see the fluid inside the radiator start to really flow through. This means the T-stat opened and fluid is now moving through the system. With a container ready to fill the system with, reach up and rev the motor to about 2.5k and as you do this, your water pump will speed up with the motor. YOu should see the level of the fluid drop down when you rev up the motor. Keep it revved and pout the water into it until the radiator is completely full. Don't leave off the throttle until you put the cap on, or it will all pour out. Put the cap on and let off the throttle. At that point all the air will be out of the system and the coolant system will be "packed".

Take it for a ride and see if its better.

If it still acts up, put a new T-stat in it. Dads in his chevelle went this past year after putting in a new one and its pretty obvoius when this happens. Fluid will be pouring out everwhere and the motor sounds like a pressure cooker about to explode! so I don't think this is your problem.

Probably either air or just a bad sensor. The bad sensor seems like the probable cause since the DFI sensor is reading normal through the entire event, as I read it. But try to pack the system first, that is free and pretty easy.

Good luck.

 

Bass ackwards. The gauge sensor is in one of the heads. The side varies with the year of the car. In his 1989, it is in the right head. ALL L98's have the ECT sensor for the ECM in the front of the intake manifold.


That is if the stat fails-closed. He can drive a 170°. That means that either he has a very cool (too cool) of a stat installed, or that it has failed in the open position.

RACE ON!!!