Engine running too cool
 

Hi all,
I have a MarkIV 454 in my ‘68 K10. It has a 180* thermostat, cheap 2 core radiator, and 2 temperature sending units on the back of the intake manifold. Now that the weather has cooled way off, I’ve noticed that the engine temp is dropping down to 140-150* at highway speeds. If the truck is just idling in park it will warm up to 180+ but it takes a very long time. I don’t believe it’s a sending unit issue because both gauges read within 5* of each other at all times.

I’m guessing the thermostat is stuck open, but before I go through the hassle of ripping into and replacing the thermostat I wanted a second opinion. Thoughts?

Re: Engine running too cool
 

My guess is same as yours -- t-stat stuck open. Check the specs for that engine though, I suspect a 180* might be too cool. A 190* or better yet a 195* might be a better choice, especially in Michigan in winter. And it won't make your engine overheat in summer.

Re: Engine running too cool
 

It can also be your electric fan on to much as well as a stuck tsat
my trucks only get a 195 stat year around

Re: Engine running too cool
 

180 Deg stat was the norm for years. Then it was raised to reduce emissions.

Re: Engine running too cool
 

If you have two temperature sending units in the back of the intake are you sure you’re not running way hotter than what your gauge says.

Re: Engine running too cool
 

I agree . I have all the mechanical sensors in the head , temps can be 20 to 30 degrees hotter in the head . My Chevelle reads 205 when the electric fans kick in they are Controlled by a sensor in the radiator that kicks on the fans at 195 water temp .

Re: Engine running too cool
 

Where is the stock sending unit location? If I understand the cooling system correctly, there shouldn’t be any coolant flowing through the upper radiator hose until the thermostat has opened. So if the thermostat is stuck open and I start the truck after it’s been sitting all night, I should feel coolant moving through the upper radiator hose, right?

Re: Engine running too cool
 

Driver side head by #1 plug.

LockDoc

Re: Engine running too cool
 

Correct. You will feel it getting warm way before the 180° is reached.

Re: Engine running too cool
 

That's on an SBC, right? Because my (70) BBC has the temp sender on the passenger's side, and the wiring appears to be stock.

Re: Engine running too cool
 

Yup, Brain fart on my part...:)..:(

LockDoc

Re: Engine running too cool
 

Well, I never noticed that the sender was on the driver's side on the SBC, so there you go. :lol: And to think that I worked on these things for many years. I worked for my BiL starting at age 15 ('67) on the weekends doing basic mechanical work. I know that they were all pretty much stock in those days, and we only fixed things, and didn't do anything custom.

Re: Engine running too cool
 

Do a search Steve.
Some bbc had the temp sensor between #3 and #5.
69 L78 did.
Factory valve covers had a clip on them to hold the wire for the sensor.

The tall deck motors had it too.

http://67-72chevytrucks.com/vboard/s...d.php?t=437017