I am really happy with the power of the truck. With all motor mods. The gears seam to be good. As does the speedo gear to seem to be pretty close.

My question is that ever since I did the motor work it gets hot. Not over heating but when it goes over 2500rpms it moves almost all the way to the hot line. I slow down and it backs off. I didn't have this problem before.

It seems like there is not enough fluid in the rad but its full and I've ran it with the cap off to make sure I'm getting flow, which I am. Could it be my fan clutch? Should I go to a fixed or flex fan?

 

You may save yourself some money by purchasing a mechanical temp gauge so you know how hot it really is. The factory gauge is not usually known for being accurate.

 

Big question, is the advance in the distributor working correctly? When you get a mechanical gauge, you might see if there is a way to read the left side (drivers) of your radiator to see what kind of inlet temp you have. If you are at speed (over 45-50mph) the fan clutch shouldn't be a concern, it's main function is low speed cooling.

 

It's related to engine rpm. Not speed. Anything below 2500 is fine. Anything over is starting to warm up. The vacuum advance is working. All the parts.

 

Dumb question, the head gaskets aren't on backwards by any chance? I have seen it done by very experienced mechanics. How hot is the air coming through the radiator? It should be noticeably hotter than the ambient air if the radiator is working properly.

 

To add to that, the top hose should be noticeably warmer than the bottom hose.

 

I did the head gaskets then put 2000 miles on it towing 15k lbs. I didn't touch the heads to put he manifold on.

I won't say 100% that they are right but at least 99%

Buy coming through do you mean internally or passing through for cooling.

Meaning it's cooling the coolant as it passes through right?

 

Yes.

I agree with the first step being verifying things with a known-accurate thermometer, go from there.

 

Another dumb question.. or two.

What pressure radiator cap are you running?
Is there a spring in your lower radiator hose?

 

An inexpensive non-contact IR thermometer is really all you need.
ABSOLUTE accuracy is pretty unimportant.
A cheap model like this one from Harbor Freight for $13
Non-Contact Pocket Thermometer
Will tell you a lot, if you know how to use it.
With fixed emissivity you need to measure like surfaces. (upper and lower rubber hoses, or various points of just the radiator itself)

A more expensive one can also tell you if one or more of the cylinders is running hot by measuring at each port of the exhaust manifold.
Non-Contact Infrared Laser Thermometer
This one reads to almost 1000*F.

 

Well my gauge held still before my mods. Now after its hotter.

I'll get a thermometer later, however using where the gauge was as a baseline should my mods have created a hotter motor?

I checked and squeezed all my lines. I did get some air bubbles out. Added some coolant. Still a little warm. The upper and lower hoses are new and the lower has the spring in it.

The lower is cooler than the upper but not a huge amount its hard to tell with your bare hands.

There is no mixture of coolant and oil either in the pan or the radiator. Also whaen it's running there is no exhaust in the rad.

 

The gauge works by grounding through the intake manifold.
New gaskets, thread sealant, whatever, can and will change your baseline.
Even the voltage regulator in the instrument panel will affect the factory gauge.

This is why it was suggested to get thermometer.
Then at least you have a number to go by.

The radiator cap will raise the boiling point by ~3* per PSI.
ie, a 15# cap will bring the boiling point up about 45*F.
You might not think about that, but hotspots will boil and vapor is a poor coolant. It's a vicious cycle.

I had a vacuum leak at tree in the back of my manifold.
The lean mixture in one cylinder was enough to raise coolant temp and thin my oil enough to drop pressure.
Never heard any knock, and the truck ran fine.
That's why I suggested reading each exhaust port.

 

Exactly!!!

 

Alright I'm convinced. I'll get the thermometer and report back.

also about he rad cap. is a higher boiling point a good thing? Please explain.

 

It's not about raising the temperature.
More pressure (to a point) will keep coolant from boiling and leaving hot spots in the heads.
It can't do it's job as a vapor.
IIRC my 460 calls for a 14 Psi cap.

But you're not even sure that you have an overheating problem without measuring.
The fan isn't really needed on the highway. There should be enough air flow at those speeds regardless of engine rpm.
What are the ambient temps right now where you live?