[dieselfumez]

Still trying to figure my old truck out, but I did run across something. I was checking it with a snap on scanner, when started up it ran open loop until about 125 degreesthen went closed , but while at operating temp (185-190) it switched back to open loop. I was told by another mechanic he did not think that it was supposed to do that. Anyone know what loop it should be in and if it is wrong what would cause it? No codes are present, 88 1/2 ton 2wd 350 tbi. Thanks for any help!!