Operating under temp.

Hi all I having an issue with my 77 K10. The truck will warm up to 190° at when not moving. As I drive it cools down to 160°.

I've been fixing this truck up over the last couple months so here's what I've replaced.

New Radiator (Old one was leaking)
New T Stat- 195°, replaced again tonight, just to ensure that wasn't the issue.
New hoses
New Mechanical Temp gauge, wanted to ensure it wasn't a bad reading on the factory gauge.
New heater core (old one was leaking)
It had a flex fan on it, went to the bone yard last weekend and got a clutched fan from a 80's square body
Builds and holds pressure
Makes good heat when sitting and getting to 190°, makes poor heat when driving and cools down to 160°.

I'm in Ohio and it's about 20° outside tonight.

I even blocked half the radiator off with cardboard. Now when driving it runs about 170°

Any help with this issue would be appreciated, Thanks!

Also I should add, I installed a new timing chain, plugs and wires.

I just double checked the timing and firing order. No issues there. At the moment the truck is running great and has no issues other than not holding temp driving.

Thanks!

You said you installed a new radiator which is almost definitely aluminum (aluminum exchanges heat better than brass/copper), and you also said it's about 20 degrees out, and the "problem" only happens when driving. Pretty sure there's your answer. You have cold air flowing through a nice new radiator, and well, it's bringing down the temperature of your coolant. You even said it cools less when you block off part of the radiator, so you solved the mystery on your own!

Obviously timing and firing order would have nothing to do with your cooling system. Dude, it's cold out. It's gonna make your engine cooler too. Good thing it's not overheating. Don't worry about it, your truck is doing what its supposed to be doing. If you want it to run hotter, block off more of the radiator

My 77 k10 calls for 180° therm. And at 20° mine runs cooler like that.But my heater works fine enough

Got ne Pix noob?

either guage is innacurate or thermostat is opening for too long or too far, (try another one, especially if its a cheapo crap one?) or that radiator really cools extra well. the thermostat is a 190 one right? is the water pump stock flowor a high volume? if its a HV one thenyou may want to go to a stock one with that alum radiator. other than this i have no idea.

good to get rid of the flex fan.. those things are useless and dangerous. clutch fans are the best.

Yes it is a 195 T-Stat, and a normal flow water pump. The only thing I found to be odd was when I ordered the rad. I ordered one Without AC; 28 1/4 inch x 19 inch Core. When I went to install it, it was too large. Ended up getting a 28 1/4 inch x 17 inch Core; With AC. That seemed to be an exact fit. Maybe the wrong one? I don't have A/C.

I don't have much to add other than my 79 runs really cold, like it rarely comes off of the "C" mark, and my truck kicks out the heat like you wouldn't believe. Maybe check that everything is proper after the heater core replacement?

Maybe 195° is insufficient in your neck of the woods. They make a 210° or similar temp thermostat..

I found a 210°, I'm gonna give that a try here soon. Right now it is about 15° outside. I have the radiator almost completely block off with cardboard. Sitting at an idle it'll get to 195°. Driving down the road it'll drop to about 185°. Which I'm happy with. Still shouldn't be required to block the rad off that much, I wouldn't think.

I agree, it strikes me as unusual BUT! that IS awfully cold. There's no harm found in running a 210, heck, it might run better.

Running a 210* thermostat will allow your oil to get a smidge warmer and evaporate any water moisture in it. As long as you have the right mix of coolant, 210 is fine.

I think a Tuned Port Injection thermostat is factory 210°.

Where'd that dead horse run off to?

before changing thermostats, block off the entire radiator. I lived in Alaska for 8 years and half of that time was in Keni and Nome. We always shoved a piece of cardboard in front of the radiator for 100% blockage for winter driving.

When you have the coolant drained again,you could check your temp sending unit.I’m sure it’s ok...check it anyway.I’ve never keep up with original gauges,but my temp unit is plumbed into the head.Not sure if placement has much to do with it