Something not right...

[hilltopfarm]

I finally started my new engine up yesterday with no issue's other than the one I am about to describe!

So I started it and the usual knocking occurred for about 2 min while everything seated, then went away. I noticed that the coolant temp started to go up very quickly (w/in about 30 sec of start) then it continued to go up to almost the redline before I shut it off. Felt the upper radiator hose and it was cool, engine was not that hot either... Put in a new thermostat when I put the engine together. Also replaced both of those coolant temp sensors and the housing. My thoughts are that maybe there is something wrong with one of those sensors (or maybe its the wrong one!?)... Any thoughts anyone??

Thanks!!!

 

[snake]

It didn't get that hot that quick so either it has an air pocket in the cooling system or the sensor is whacked. Or the one we all dread- the head gasket was wrong and it blocked a water passage...

 

[hilltopfarm]

It didn't get that hot that quick so either it has an air pocket in the cooling system or the sensor is whacked. Or the one we all dread- the head gasket was wrong and it blocked a water passage...

It better not be the latter. The heads were installed by the company that re-manufactured the engine...

 

[hilltopfarm]

What would be the easiest way to "burp" the system? Leave the rad cap off and run the engine??

 

[Mac]

The way I have used before is to leave the cap off, recommended to run a garden hose in there and open up the drain valve and with v-8 at least, keep the rpm's up to 1200-1500 rpm, forget how long They do tend to get a bit hot.

 

[hilltopfarm]

So I don't risk overheating the block (and heads) during this process do I? Are there any precautions I need to take? I guess just do it till it no longer bubbles?

Thanks

 

[wildbill23c]

One way I have to do it on my 2.8L is to take one of the hoses off the heater core and let the truck run until it starts pushing coolant out of the heater core. Most likely that's where your air pocket is, which is why its heating up so fast. If you just got the engine, remember that engine is dry, its gonna take a bit to get the coolant through all the passages, if there is air trapped in there its going to take a bit to push it out.

 

[adsm08]

I like to fill the radiator with coolant and then once it is topped up I pop a heater hose and pour some coolant down there until it comes back up out of the heater core. This pushes most of the air in the system up out through the high point of the system and eliminates the bubble issue most of the time.

I would tend to agree that your temp gauge running to the top was not an actual overheating issue. Keep in mind that there is almost no coolant circulation through the upper rad hose until the engine gets to it's operating temp, and overheating temp is 50* to 100* past that. If the upper hose was cold, it wasn't overheating.

The coolant temp sensor on the other hand is not meant to read air temps. It is meant to read water temp. If you expose it to air and ask it for the temperature it will give you a reading that is drastically higher than accurate. That is actually how I know that the 4.0 Explorers have pushed the bubble out when I do radiators on them. I'll fill them up, let them come up to temp at idle in the lot, and then cap it and go drive until I see the temp gauge spike like that. Once the bubble passes out into the radiator the needle comes back down and I top it off.

 

[hilltopfarm]

Thanks for all the helpful replies!

I got the think bled out, ended up running it with the cap off for a while with the heater on "hot" until I saw air bubbles coming out...it took a little while, probably about two-three minutes to get them all out.

After that I took it for a drive and did the things that the engine remanufacturer recommended to break it in. I let it sit overnight and checked the radiator in the morning and sure enough it was down three-four inches...

 

[RonD]

Cooling systems with overflow tanks(pretty much all of them these days) are self purging unless there is an air lock, which is probably what you had to start with.

The rad cap has 2 valves in it, the larger one is the positive pressure valve usually set for 14-16 psi, this holds pressure in the cooling system until the rated pressure is reached and above that pressure coolant is allowed to flow into the overflow tank, coolant expands as it heats up, that's where the pressure comes from.
The pressure in the system raises the boiling point of the coolant.

The smaller valve inside the larger valve on the rad cap is the negative pressure valve.
As coolant temp goes down so does the pressure, coolant contracts, when the pressure inside the cooling system gets below 0 psi(relative) the air pressure(15 psi at sea level) in the overflow tank pushes the coolant back into the rad via the smaller valve.

So any air in the system will find it's way to the top of the rad, and at the next heat cycle the air will be the first thing to be pushed into the overflow tank where it will bubble to the top and be out of the system.

Pretty simple system.

But it does rely on both valves working and that the overflow tank is never dry, that's why there is a "Cold" level mark, if the overflow hose is cracked or tank is dry it will suck air back into the cooling system, air is easier to pull in than fluid.

So your rad being down 2-3 inches would mean either the overflow tank was empty, the overflow hose is cracked or the small valve is bad.

Collapsed rad hoses on cold engine are a sign of a bad small valve or blocked overflow, pressure can't be equalized.
Overflow tank can get debris inside, coolant can come in but can't return because debris settles at the bottom and blocks the return.

 

[hilltopfarm]

In my case the overflow tank was empty. The system has new hoses and new rad cap, so it wouldn't be those... Thanks for the helpful info!!

 

[Road Angels]

Good write up RonD I also back fill the heater hoses but I also use a safety themostat and hand operate it, and drill a small bleed hole in it even if it has one already, I have even let them sit over night and had the water level go down as well as park them up hill or on ramps to help purge air out

 

[85_Ranger4x4]

I fill it up nearly full and squeeze the upper hose to sort of pump the coolant that way. I get in another easy half a gallon doing that, I don't seem to have any bubble problems in the either the stock 2.8 system or the morphadite system currently in my truck.

Don't fill it too full or it will come out the fill hole when you squeeze it. I fill the reserviour (from a '93 Explorer) to the cold line so if it wants more it can get it too. My stock puke tank didn't have a hole to fill it from so you had to baby it in through the overflow hose... it was a pita.

 

[hilltopfarm]

Thanks for the helpful info!