I just got my car back on the road and I noticed a problem the other day on the highway. My autometer gauge was pegged at 250 degrees while driving on the highway. I took a look at the coolant temp on my laptop and it read 170 (hooked up to the sensor on top of the intake through my FAST ECU). I thought it was weird and figured maybe I burnt the wire for the gauge near the headers or something. well yesterday, I watched the gauge again and after 5 minutes of driving ( 30 degrress out in the morning) the needle started climbing to 250. The display on my laptop for the FAST setup showed a steady climb as well but it was about 20-30 degrees behind the gauge. The display went to 222.2 and then stopped climbing. Then all of sudden, the gauge just started going back the other way and finally stopped around 170. the display on the laptop did the same. I drove the rest of the way home on the highway and it never got past 200 until I hit the city. Then it started all over again. What gets me is that if I go open the hood, it isnt that hot under there and the water isnt boiling or anything. Whats even weirder is that it overheats 5 minutes after starting it up in the morning as I am driving on the highway and its only 30 degrees out. 5 minutes later, she runs fine while cruising on the highway. What gives here? my entire cooling system is new and I am running a Proform electric water pump which does work.

 

Sounds like an air pocket has developed (or never got released) in the cooling system. As for the gauge and why it is giving different readings, where is the sensor located?

 

the sensor fo rthe gauge is on thje drivers head the sensor for the FAST is on the top of the intake just under the TB. I t used to be on the passenger head but the wire kept burning becuase it was so close to the header pipe. So, witht he sensor sitting up high near the front of the engine it will get a slightly low temp reading then the one on the head

 

Is the sending unit still in the head?Did you try using a fibeglass jacket on the wire?Or you could use NiChrome(nickel/chrome)wire.Stekman has a very good point on the air pocket.They will cause symptoms like your having.

 

Ichecked out the cooling system this morning and I needed to add a little bit of water to it. I also let theengine run with the cap off the radiator. Hopefully, any air got it if there was any in there. Iwill have to wait and see when I go for ride later.

 

For kicks and giggles, swap the 2 sensor locations if you can and check the readings again.

 

Thats not an option. The wiring will have to be lenghtened and I am not cutting the connectors off

 

The I would try to find a way to isolate the sensor from the exhaust heat.

 

well I was thinking about this today and when I change my oil, I am going to get in there and put some fire sleeving on the sensor and the wire and see what happens

 

On a side note, try bleeding the system, perhaps try drilling a smalll hole in the thermostat and reinstalling it.

 

I thought the system in our cars constantly bleeds intself since the system is not sealed.

 

I did too, until my old Caprice with the cooling system off my Camaro did the exact same thing, got REAL hot, REAL fast, then after a few minutes, dropped to normal temps - every time I ran it. Drilled a 1/8" hole in the stat and reinstalled it, problem gone. It happens.

However, I have to think the main problem is the false reading the aftermarket gauge is reading, rather than an actual air pocket.

 

Just remove your thermostat. This will keep the antifreeze running through your engine the whole time your engine is on. Or you can just go out and buy a lower thermostat.

 

And that would be even worse off than he is now.

 

Make sure that your air dam is in place. Lost mine and the temps went wild. Okay on the highway with air flowing, overheating in the city at lights.

Reinstalled the air dam. No problems.

Jim.

 

Cool on the highway and hot in the city Q; 1.Is your fan coming on? 2. Do you have the thermoustat installed upside-down? 3. Have you had the intake off and used the wrong gaskets that might not match the water ports between the heads and the intake? 3. What condition is your radiator hoses in. Your new electric water pump may be overpowering your bottom hose if it's weak and colapsing it when the therm. opens and reducing the coolant flow. OR, you could just have a partialy blocked radiator core thats just not cooling fast enough in city driving but manages to do better at highway speeds from the increased air flow.

 

I think I fixed the problem. I ran the engine with the cap off for a little while and then re topped off the radiator and overflow. Im thinking there was air in the system. When I orignally put water in the engine and ran it, I never had my heater hooked up and I bet the air was being trapped in the heater hoses and heater core. I could be wrong but hey, I fixed the problem. Thanks for the tips guys.