Wierd coolant temp condition
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
Wierd coolant temp condition
Here is a wired one. I started the new motor and let it fun for about 5 minutes or so. The car is still up on stands because I had a coolant leak. Ok here is the wierd part. I'm in the car watching the oil pressure and coolant temp. I run a 180 stat and have my fans set to come on at 185 degrees. The coolant display on the dash kept climbing past 200F up to 210F and the fans were not coming on. I shut off the motor and checked to see if the fan relay got knocked loose or something. It was OK so I started the car again. No fans on again. Then I noticed that on Diacom, the reported temperature was 175 degrees. So I had 175 on the scanner and 200+ on the dash.
I think the sensor the the dash is the one screwed into the intake water jacket and the one for the ECM is located in the passenger side head. Is this correct? I am running a single plane EFI intake by Jeb Burnett and my coolant temp sensor is now in the rear of the intake and not the front like on a TPI base. Could this be because of an air pocket in the rear of the heads causing poor circulation that needs to burp out?
I think the sensor the the dash is the one screwed into the intake water jacket and the one for the ECM is located in the passenger side head. Is this correct? I am running a single plane EFI intake by Jeb Burnett and my coolant temp sensor is now in the rear of the intake and not the front like on a TPI base. Could this be because of an air pocket in the rear of the heads causing poor circulation that needs to burp out?
Last edited by 89vette; Sep 28, 2007 at 11:38 AM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The dash digital temp gauge uses a sensor on the right side of the block between cylinders 6 & 8. the computer turns on the fan relay based on the sensor normally on the front of the block by the MAF. You definitely need to burp your cooling system!!!!
Team Owner
Joined: Feb 2006
Posts: 24,460
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From: sw Ohio
Theres another one that just reads the temp on the driver's side too.
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
Thanks for the clarification on what sensor does what. With my old AFR heads, I always had a higher temperature on the dash than on the scanner. I figured that the one up front was for the dash because the coolant would be hotter exiting the heads compared to the coolant in the block.
Or maybe the fact that the ECM sensor is located in the rear of the manifold and not in the front where coolant is flowing past it, it is reading low. I hope this is not going to be an issue.
Or maybe the fact that the ECM sensor is located in the rear of the manifold and not in the front where coolant is flowing past it, it is reading low. I hope this is not going to be an issue.
Last edited by 89vette; Sep 28, 2007 at 03:33 PM.
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
Yes you are correct. That operates the Aux fan. I actually wired the ground for the aux fan relay to the primary fan relay. This way when the ECM turns on the Primay fan, it pulls in the aux fan relay also.
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,388
Likes: 42
From: Murrysville PA
The problem turned out to be an air pocket. I don't want to take any chances so I'm removing the intake and welding in a 3/8" bung in the front thermostat housing to mount the sensor. This way there is always coolant flowing past and there is no chance of an air pocket. Most other users of Jeb's intake have two pipe bungs in the front as well as the rear. I only have one in the front for the coolant outlet to the heater core becasue he fabricated it the cross over. One good thing is that it only takes a few minutes to get the intake off.
