New engine build getting too hot

Is it normal for a new motor with a fresh hone to run extra hot while it's breaking in? Or should I be concerned there's a cooling issue? I've never broken in a new motor with 0 miles on it, so I don't know what's normal or not.

It's going to the dyno in a few days, so I'll find out one way or another then if it's going to overheat. That's where I'm going to do the proper break-in and

I've got my new motor built, and started it up for the first time, and ran it at a high idle to break in the cams. I'm concerned about the temps it's hitting. I started it up once more to do some more idle testing and rough the idle control just well enough so that it doesn't stall when I let go of the pedal. And I logged it both times, and the temps aren't normal compared to my old motor.

My old motor used to idle stable at 93C. This one from cold got up to 94.5C and stabilized there for 20 seconds, then it started slowly creeping up again. It reached 98.5C before I shut it off, and it was still rising.

get tuned.

Has the cooling system been bled correctly? Thermostat mounted in the correct orientation? All of the hoses connected in the right order?

What does the radiator temperature do? Is it getting hot or staying cool?

Also, what thermostat temperature are you using, is it the same engine sender, is it the same vehicle's gauge/display?

I once had freshly built engine going too hot at idle at first start up - the reason was broken wire to one of the radiator fans, it just wouldn't kick off...

The rad fans are working fine, and all plumbing is correct.

The t-stat is advertised as 180F, so about 82C.

It's just using pure distilled water with water wetter added. And the system was vacuum bled, there is no air in the system for sure.

I take it from the responses so far, that it's not normal for a new engine build to run hotter initially.

I've never seen an engine run hotter because it was newly built.

Even if I vacuum bleed the system after a new build, I still use the funnel (https://www.lislecorp.com/specialty-tools/24780-spill-free-funnel-18-pc) and make sure there's no air left in the system. Sometimes there is. Also could help indicate if there are cylinder pressure going in the cooling system.

It's vacuum bled AND it's a self-bleeding coolant system. There is no cap on the radiator, just on the reservoir. You could say that this system is it's own funnel.

The way it works is there's a pair air bubble lines from different points in the system that lead back to the reservoir. As long as coolant is flowing, any trapped air will work itself out. All I have to do is keep the level up in the reservoir.

Have you double checked cam and ignition timing?

Hi Matt,

As the other members have stated, A new motor should not overheat. Even though the cooling system was Vac-bled during the initial fill, it does not mean the system is completely air free. The vacuum bleeders are helpful; however not 100% effective.

On stubborn vehicles, I will still use the funnel fill adaptor on the reservoir as it moves the high point upwards in the cooling system and sometimes tilt the vehicle's nose a few degrees upward to coax any remaining air pockets forward.

I think I figured out the problem. The problem is me installing every "go-fast" part I could get my hands on.

I installed an underdrive crank pulley AND an underdrive water pump pulley. So the pump was being double underdriven. So at idle there was insufficient coolant flow, but revved up to 3000rpm and above it cooled fine.

I'll put the regular w/p pulley back on, and I expect that will solve it.