Okay guys, I have another question. As many of you know, I recently did a 305 to 355 swap in my 1986 K10. After many set backs I finally have it running, thanks to some great help on this site, and my next door neighbor! Yesterday, I put all the hoses on and finished hooking things up. All it needs now is the clutch slave cylinder bled out and she's good to go other than some tuning.
The question I have stems around the initial start up and camshaft run in for the first 20 minutes. I started it up, ran it right up to 2,000 and never let it under that or idle. After about 2 minutes of run time, the temp gauge started climbing up towards the 220* mark. Another minute it was just past 240*, so I immediately shut it down! I let it cool back down, but I felt the upper hose, and it was still cold! The thermostat hadn't opened up yet, and I saw NO obvious signs of overheating.
So, I let it set until it was completely cold, and decided to make a second run at it. My neighbor had just come over at this point. Same thing. Gauge started going in the red, but my neighbor was standing there holding the upper hose in his hand, as the thermostat had JUST at that point opened and the upper hose was just starting to get warm. I had the heater on full blast while I had it running. The heater hoses were too warm to hang on to, much warmer than the radiator hoses. Strange to me, since the 305 that I had in it never had any overheating problems, and the 355 just didn't seem to me to be running hot, but I hated to take a chance on a fresh build. It has a brand new 192* thermostat in it that I installed during the build.
So, what I did today was go to O'Reilly and pick up a new Mr. Gasket radiator cap that has a thermometer built into it just like this one:
http://www.oreillyauto.com/site/c/detail/MRG2/2471S/03357.oap?year=1986&make=Chevrolet&model=K10%2BPickup%2B4WD&vi=1300587&ck=Search_C2021_1300587_259&showStores=true#at I put it on, and had my oldest son stand in front and watch the thermometer in the radiator cap while I tried the cam break in. I told him if it got to 230* yell and let me know so that I could shut it down. He watched it the whole 20 minutes that I ran it. It never got above 200*. So, after I ran the cam in, I let it idle, and it dropped back down between the 180*-190* range. However, the temp gauge in the cab is beyond spiked, but I still have no obvious signs of overheating!
This 350 is out of a 1973 Chevrolet Impala. The temp sending unit out of my 1986 305 head would not fit the 1973 993 casting head since it was way too small in diameter. So what I did was go to O'Reilly and get a temp sending unit for a 1978 truck with gauges.
Question is, could the earlier temp sending unit be incompatible with the later wiring harness? One other thing that I can think of is that when I put the sending unit in the head I used Teflon tape to make sure that I didn't have any leaks. But now I'm wondering if doing that may be causing it to not read right, and in turn be causing the gauge to be out of whack? I know it's not been overheated since the thermometer in the radiator confirmed that, so what gives here? ...Joe
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