I'm trying to finish up my project.I have a 92 740 wagon, non-turbo. Recently replaced cylinder head and gaskets,plugs,wires,timing belt and soo much else.It now starts,idles kinda strange (hunting). It now has a check engine light that it didn't have before. shows code 123,so I bought a new coolant temp sensor and put it in.I could only hand- tighten it,but it sends an erratic signal to the gauge.The connector crumbled so I cut one off a 940 and spliced it on there best I could .I thought once i got the sensor on there the code would go away.Also the heater is slow to come on and the electric cooling fan isn't coming on either, the lower radiator hose gets way hotter than the top- thermostat stuck closed? Its a newer thermostat.Also have a newer water pump.I feel like all these symptoms are related and rather than tacking them individually, I should just zero in on the thing that's causing this. Any ideas? I need a fresh view because I'm out of ideas! Thanks a bunch !!

 

You have done so much, it's very hard to diagnose what could have gone wrong. And there are many possibilities. You have a cooling problem, obviously: an air pocket? No circulation, caused by the pocket, may be a thermostat... The coolant temp sensor doesn't sound right, hand tightened? spliced? Hard to evaluate...

 

I guess I'll replace the thermostat and see what happens. Thought about getting a new fan relay but I only have one relay on that side-I guess that's the noise suppression/fuel injector one. It doesn't operate the fan too, does it? If so ,maybe I'll replace that too. After that it's off to my Volvo guy's shop! Still= I keep thinking if I can tighten that temp sensor,that might bring me relief. I read all the threads about removing the manifold,etc. I dont wanna do that again! I'll go buy a new tool if I have to. In 4 months my 740 will be historical! I'll be hysterical......