My current build is overheating after I drive it for 20 minutes.. From what I can tell it blows about a gallow of coolant out the overflow, Once enough coolant is lost it overheats...

The build is a mildly cammed 6.2 liter in a C10. The cooling system is starts with a Coldcase radiator running a full shroud and 2 fans. Thermostat is a 160. Radiator cap is 16#'s.

I have "burped" the system while on a steep hill and I'm confident there isn't an air pocket.

The water pump is new and I can see plenty of flow thru the radiator once the t-stat opens at temp.

It WILL NOT overheat at idle, I've run it at temp for 10 minutes, stays at 180 ish.

It runs down the road at 180ish for about 10-15 minutes before it starts to climb toward 220ish. And this isn't stop and go type driving, mostly 30-50 MPH cruising.

Both FANS work as expected

Any ideas on what I should be looking for or how to test it?

Could I have a defective radiator somehow?

Are the FANS not up to the task?

ANY HELP would be great!

 

Little more info....

Just double checked and at idle it is NOT blowing fluid out the overflow.

Take it for a short ride and it shoots coolant out the overflow, enough to spray the underside of the hood! It's the RPM/LOAD that triggers the ejection of coolant.

Could this be a Head Gasket? Combustion leaking into the coolant and pressureizing the system?

Man wouldn't that suck...

 

Perhaps you have a blown head gasket or cracked head pushing compression in the cooling system?

 

The more I think about it that’s what’s going on.

oil level is okay but that doesn’t mean combustion gas isn’t going the other way.

picking up a coolant test kit now just to double check

 

Are you positive you have all of the air out th system? Air can be a major pain in the *** sometimes. I'd like it run with the cap off and the front jacked up for a good 30-45 minutes and squeeze the bottom hose a few times to make sure to push the air out.

 

ALMOST 100% …

Thats why I’m getting the tester

I have the perfect hill to burp a cooling system and yeah you gotta let it get good and “angry” for sure.

So pretty sure Its gonna be the head gasket. It has all the signs and no way this hobby is gonna let me off the hook with a bad radiator cap so back into the shop she goes! Damit

 

honestly man I thought the same thing with my truck once before, it would do the same thing and I swore it was the head gasket and it ended up being air trapped. Can you crack the hose that hooks to the steam ports and let some coolant flow through like that?

 

So on my earlier LS swaps I would get the engine up to temp. Pressure in the colling system. Then I crack open the temp sensor in the left head to bleed off any air. Be careful its hot and sprays around a bit.
But I finally broke down and bought a "Maddox" MH-1B cooling and refill kit from Harbor Freight. Works like a champ. It sucks all the air out of cooling system. I think a few years ago it was $70?

 

Its kills me everyone working so hard to burp a cooling system when amazon has a vacuum filler for so cheap. I fill my car with a vacuum filler and have never once had a burping problem. Sometimes your money ahead buying the right tool. Just saying.

 

How many miles are on your current build?

 

Less than 1000 miles since I got it out of the machine shop… it’s been going on a long time, like 400-500 miles. I’ve been chasing it as a leak. Also been checking the oil frequently (because it’s a new build) nothing extra on the stick.

This however tells a different story… She’s coming apart, again.. Note the car in the pic has a different issue and already has the heads off and in the shop.

 

That sucks... seems like you have alot of head/gasket issues...operator or builder issue?

 

Pretty sure this a head issue.. can’t say for certain but for sure don’t want it to be the block so the heads are going to the shop later this week.

The Nova had old 799’s that needed help so they are in the shop turning into rebuilt 317’s to bring compression down about a point. Should be picking them up end of the week.

Installing heads is pretty basic assuming you can read, I can read, it ain’t me.

 

MLS headgaskets simply don’t fail that easy. I’d look at a head being cracked or even a sleeve issue. A lot of times you can see a crack in a sleeve better from the water jacket side (behind the sleeve) than if you’re looking directly at the cylinders. Use a good LED penlight and carefully examine all the water jackets down around the cylinders. The aluminum shows bulges or cracks pretty well. Maybe this thing was previously hurt and you weren’t told about it…I hope I’m wrong about it all for your sake.

 

OKAY.....

Long story short, head gasket failure. #4 hole was very clean when I got her apart. Thought the head might be an issue so I had both of them tested by the shop that did the work on them to start with.... about 1000 miles ago.

NOPE, not the head... wasn't sure how I felt about that BUT when I brought the heads to the shop I brought the gaskets and despite the fact he might as well be blind the guy was convinced there was a head gasket issue. So I threw the heads back on a BLOCK that went thru the shop 1000 miles ago with half of me (the old half) thinking this is a stupid idea and the other half (you know what half this is) telling my to send it...

Truck fired right up and went striaght to 220 on a 180 t-stat... WTAF is going on?? I had her on a hill and burped her like I do... TRY IT AGAIN.... Are you shitting me, right to 220 again. Oddly enough the cooling system does not test for combustion gas nor is the oil level rising... BUT THIS HAS TO BE THE BLOCK RIGHT... CRAP!!! So I go to bed, don't sleep great, decide to do everything except deal with the truck all day.

Okay it's the next day late afternoon and I'm finally convinced I'm buying a long block from TSP with expidited build/shipping.added in and yeah I was still was ready to pull the trigger and buy my way out of this frigging disaster... so at this point I figure I have nothing to lose and try burping/testing her one more time. HEY.... She's holding at 185 with no combustion gas detected, take her for a short drive, 192 max.. let her idle for 10 minutes, 185... HOLY CRAP

WHAT CHANGED, the hill I used to burp her on... I couldn't use my "go to hill" due to some workers were in the way so I used a hill in my field instead.That resulted in roughly 24 hours of anger, not great. So to the guy saying I should buy another "suitcase tool" (I have like 20 of them and was not keen on another) to vacume fill the coolant you are right, ordered it before I wrote this.

 

Weird

 

The good news is the truck is up and running great. Put about 40 miles on her today in the heat and nothing is complaining.

 

glad that you found the problem.. I also had a overheating issue very similar to you. mine turned out to be a defective waterpump!. it was a weird deal as well, the pump would be fine at idle, but under load it would not work correctly. EVERYONE & I mean everyone, said bad gasket and the heads needed to be pulled. my engine guy swore up & down that the gaskets were correct. he finally did the work & sent me picture of the pulled heads, put new gaskets on and ..... same issue. he finally just "for fun" put a new WP on (actually a used that he KNEW was good &... EUREKA!! the heating issue was fixed. he put a new pump on & I have been "heat free" for 5500 miles!! this was on a '86 C10 with a 2011 sub 5.3 factory rebuild. I drive the truck every day.

good luck!!