I just finished flushing the cooling system refilled it and purged the air out with the fittings on the thermostat housing and below the throttle body. When I first started it the digital gauge said 142 and the service engine light was on. I let it run for a bit and the light went out and the temp dropped to something I could believe. I figured I still had air in the lines so I burped it again, got a little air but not much. After doing this several times it still starts off at 142 degrees with the check engine and after just letting it run for a bit I noticed when it hits 220 the fans come on and the temp drops to 142 stays there with the check engine light back on again. After noticing this I watch on startup and the fans come on right away then too.

Is it normal for the fans to come on right away on startup with the AC off? Is 142 some sort of code and not what the sensor is reporting? Any ideas what might be going on here? I could not find anything helpful in the FSM or in a search so I am at a bit of a loss right now. I guess the next step would be to drive it around burping the system once in a while but I do not like the idea of the ECM getting the wrong temp reported and not knowing how hot every thing really is. The analog gauge stays fairly normal.

Sorry it’s so long but I sure could use some help with this one.

Thanks.

 

With both fans coming on at start up, I'll bet you have a sensor not connected correctly. I'd check your connection on the IAC and CTS since they are both in the area you were working on. The ECM is setting codes so you could pull them if all else fails. If it was running OK before the work, it is probably something this simple.

 

That makes a lot of sense, Whats a IAC and CTS and where are they?

 

would drilling the holes in the thermostat really get rid of this problem ?

 

Fans coming on at startup is not normal, only in test/diag mode. When your burping, did you raise the front up, helps, keep idle @ 2500 thru process and until you cap the radiator, check the sensor at the radiator and make sure still connected.... check for error codes, reset, startup and check again..

 

The CTS is the coolant temp sender and is mounted on the front of the water pump. The IAC is the idle air control on the r/side of the throttle body. Also check the air temp sensor which is mounted in the side of the air horn. As stated above the car is going into diagnostic mode on start up which indicates possibily a unhooked sensor. Did you remove the knock sensors to drain the block? If so check the connectors on both of them. Like I said, if all else fail, pull the codes.

 

I checked the sensors and they were all still hooked up but I wiggled the connection anyway. Then I started up the car and it started and ran normally until the temp reached 194, I Think that’s when the thermostat opens up. Well after sitting at 194 for a minute or so the temperature started jumping around fairly wildly, about 160 to 190 then went back to 142 with the check engine light back on. I went out and wiggled the connectors again but it did not help. I will be pulling the codes next weekend and hopefully they will tell me something.

 

There you go. Pull the codes and report back.