Engine Runs Warm, Need Help with Cooling System

[dgheinen]

My 68 C10 was originally a straight six. One of the previous owners put in a 350 sbc from a 72 K10 (I checked the block code) and I believe he must have used the straight six frame mounting locations. The engine sits pretty close to the firewall, much tighter than my 78 Corvette does. Also, the front of the fan is about 3 inches away from the rad shroud. It usually runs about 190-195 degrees when driving down the road and has reached about 210 once or twice when sitting in traffic.

Last Friday it was really warm here in Seattle, and the temp rose to about 230 before I could pull over. I shut it off and waited for everything to cool to about 160 degrees and pulled the rad cap. The radiator was about half full. I checked the dip stick and it looked perfect, no frothy, milky substance in the oil at all. I topped it back off and drove the rest of the way home (about 15 mintues) and the temp was hovering around 190-200 the whole time without ever really coming down or going up from there. When I got home and let it sit, the radiator is lower by about 1/3 again. Somewhere, I'm losing coolant. When I popped the hood originally on the side of the freeway, there was some small pockets of coolant on top of the intake at the front next to the heater hose. I'm thinking I may have a couple of issues here.

1) Fan needs to be ~1/2 in the shroud. I think the best solution is to extend the shroud, rather than moving the drivetrain forward and needing a new driveshaft.

2) Thermostat may be a higher temp (not a 180) or may not be opening all the way, which may explain why the motor likes to hover around 190.

3) Coolant leak somewhere. I'm thinking not a head gasket as the oil looks very clean. Could it be an intake gasket? Or possibly a crack in the heater hose.

What do yall think is the best approach to figuring this problem out? Thanks in advance.

Damon

[davepl]

If it's cooling OK when rolling down the road then it's a shroud/fan issue of some kind. Make sure your shroud is installed, 1/2 in as you say above, and well-sealed to the radiator (I use weatrerstripping, that might be overkill).

A head gasket leak wouldn't show up in the oil (or anywhere, really) although it could be detected in the coolant via a sniffer or sometimes as bubbles. But if it's not overheating once rolling, you're probably not looking at a head gasket.

Get the fan/shroud/thermostat up to at least 1970 factory condition and you'll likely be OK, but even if not, that'll give us all known starting point.

[dgheinen]

I just did a couple things to work on the truck. I replaced the thermostat, in case it was failing to open all the way. It was a very old looking Stant 195 degree thermostat. I noticed that the water neck flange was also chipped, and had caused a fairly substantial leak. Also, the heater hose was leaking as I suspected, and was made much easier to diagnose by cleaning up the intake. I filled the radiator back up and replaced the thermostat with a 180 degree thermostat, and the truck runs well now. No smoke, temp stays around 170. I believe my temp sensor is off. Stant's website says their thermostats open around 10 to 15 degrees warmer than the advertised temp. That also makes sense as to why the coolant was boiling at only 230 degrees. I checked with a infrared digital thermometer and it was reading right around 180. So I think I'm good there. While I was at it I also replaced the old radiator cap with a new one, just in case. I'm sure we've all had a case of the "eh, might as well".

[Stocker]

Sounds like you're on the right track. Be sure to get the fan into the shroud outlet, one way or another.

Other suggestions: If you don't have a good clutch fan, get one. Flex fans and fixed-blade fans aren't nearly as effective. Also, get a coolant recovery tank (requires a radiator cap for a sealed system) so the radiator will always be full. Once the system is leak-free and working well, make sure it has a 50/50 mix of water & antifreeze.