Why so hot??

[79jasper]

If it immediately starts rising, you have a leaking head gasket, or possibly cracked cylinder wall or head.

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[SPR1NK]

It ran for a few minutes before it started riaing and rose really really slow, is that still an indicator of that?

 

[IDIBRONCO]

It ran for a few minutes before it started riaing and rose really really slow, is that still an indicator of that?

Probably not. There's a lot of pressure in a cylinder even on a gas engine. These have way more. High pressure goes through the cooling system quickly. When the coolant started running out, was it all coolant or was there any "air" pockets coming out too? Sticking to your previous testing, the numbers at the radiator inlet and outlet do indicate a coolant flow issue. Having it run cooler by removing the thermostat. almost eliminates the radiator for me. If you want to, you could remove the radiator and try running a garden hose through it. It's not real scientific, but if the radiator's upright and you run the hose in the inlet, the water should never back up inside and start coming out the inlet. Otherwise, I'd go along with the boiling your thermostat idea.

 

[Thewespaul]

How clean was the oil cooler when you had it out?

 

[Macrobb]

So, if you have the radiator cap off and it's idling, and you rev the motor, does the coolant level drop, then come back when you bring the RPMs back to idle?

If so, you've got air in the system. Make sure that you've removed the darned check ball in the upper thermostat housing, and that the 1/8" passage behind it is wide open on both sides.
That will allow you to easily bleed the system by just filling the radiator and done. The check ball... doesn't seem to work. And the 1/8" diameter passage bypassing the radiator... doesn't make any difference in warmup time.

 

[IDIBRONCO]

Make sure that you've removed the darned check ball in the upper thermostat housing,

The engines that I've had either didn't have this or it fell out and I didn't bother to replace it. I agree that it probably looked good to engineers (educated idiots), but doesn't really work out in practice.

 

[SPR1NK]

We cleaned the oil cooler when we rebuilt the engine

Looked like just antifreeze when it was spilling out, didnt see bubbles or anything

That check ball can be removed? I didnt know that, thought it had to stay in there...

 

[dgr]

Everyone should own a radiator fill funnel..like this one.
Lisle 24680 Spill-Free Funnel https://www.amazon.com/dp/B00A6AS6LY/ref=cm_sw_r_cp_apa_i_OsOGDb6HXGR5K

 

[Black dawg]

Also when its running that hot if we hop out and use the no contact thermos on the rad, its usually 190ish at the inlet and 80-100 at the outlet, thermo says 220 when we point it at the block, changed gauges to make sure we didnt have a bad gauge and still says same temps

radiator top tank temp should be very close to engine temp...….if coolant is flowing. Been a long time since I measured these temps on my truck, but I do remember that.