The Stovebolt Site Forums The Shop Area Engine Shop 250 running warm

Hi guys,

I have not posted in a loooong time, but I have been reading the forums regularly. I'd love some input on a minor problem I'm having with a '78 250 in my wife's '67 Chevelle (not a truck, I know, but hey, it is a Stovebolt 6!).

I recently got this puppy up and running as this is going to be my wife's daily driver. Engine is a replacement out of a 78 Chevy truck and is in great shape. It was running rough and running very hot--I would shut it off at 240 deg. Reading posts here, I determined it could be: bad timing, vacuum leaks, bad distributor. Sure enough, found a leaky intake manifold so I replaced the gasket and properly torqued it. Then I timed it to max vacuum at idle (with vac advance line to dist. plugged). Wow, what an improvement! Finally, I replaced the stock dizzy (which was an HEI on the 78 motor) with one of those coil-in-cap HEI jobs off of Amazon.com. Drove it today, and wow, it runs like new--very smooth, tons of acceleration! Here's my only problem (and maybe it's not even a problem): I have a 180 deg. thermostat in it (with two 1/8" bleeder holes drilled, as I had earlier experienced problems with air bubbles), and now it wants to run quite warm, around 210-220 degrees once it's warmed up. I'm thinking this is too high and it should be running at or under 200 (stock thermostat was 195). Earlier I had pulled the thermostat (this was after the new manifold gasket and re-timing, before the new dizzy) and of course it ran very cool--took forever to move the temp needle and barely got up to 140 maybe (this with ambient temps in the 20s). This confirmed to me that there are no problems with the water pump, radiator, blocked hoses, etc.

So here's my dilemma: known good (I had previously tested it) 180 deg. thermostat is making it run what seems too warm, but no thermostat is running way too cool. Is there a better/ wider opening thermostat I can run? Should I try a 160 deg. thermostat?

Any suggestions would be greatly appreciated!

Is the coolant boiling and coming out of the radiator vent tube? If not, the engine is not overheating. The temp in the 200 degree range isn't excessive as long as you've got a good pressure cap. A 14 lb. cap will raise the boiling point of the coolant to 254 degrees F. at sea level. You could easily run 220 degrees or so with no damage to the engine. Chances are the radiator is a little dirty or your temp gauge is lying to you. I'd suggest using a laser pointer temp gauge and checking the temperature of the thermostat housing above and below the thermostat. Then check the temp of the water pump inlet to see how efficiently the radiator is functioning. A good radiator will drop the coolant temp around 50 degrees or a little more. Do you have a fan shroud on the car?

Jerry

Where on the engine is the temp sender for the gauge?

I ask because my 250 always ran hotter then I liked till I moved the sender out of the head and placed it right under the thermostat. I now runs 15 degrees cooler! When in the head, the sender is very close to #1 and # cylinders. When working on the water pump, be careful of the upper right bolt, its right by the first head bolt and there is barely enough metal there for both of them. Head bolt torques to 85, water pump bolt is just tight enough not to leak.

Try another therm. A lot of the therm. we get are not good. I stopped replacing therms. as a regular maintenance item. If it is working good I reuse it.
George

Thanks, Jerry!

Coolant is not boiling over and coming out the overflow, and there is no fan shroud. It is a new aluminum radiator. I believe the PSI on the cap is 14. I don't have a laser temp gun, but maybe it's time to invest in one!

Joe,

Temp sender is in the head, right by 1 and 2 cylinders, so maybe it's just what you mentioned. Based on this and what others have said, I'm going to stay calm and not mess with it, as long as it stays below 220. Thanks!

Thats where mine was. I would always see the gauge rise way up to around 210 or so the fall back to thermostat. It did this overtime it was parked and had time to cool off. Once I moved sender, the temp always stays right at thermostat. I believe the water is much hotter right at the cylinders but mixes with cooler water coming around the back side of the head, by the time it all gets to the thermostat housing it has averaged out. My housing had a port that wasn't drilled or tapped, but that was easy enough to fix.

That is what I'd do, Tyler. My 235 (with a 160 degree thermostat) runs between 175/180 (cold day) and up to 185/190 in traffic on a hot day (known good mechanical temp gauge). I have an aluminum radiator (3 core) with a fitted shroud and a 2700 cfm cooling fan in a puller orientation with a temp controlled switch.