Coolant flush troubles, quickly boiling over?

I recently swapped in a 4.6L stroker in my 89' XJ from another 90' XJ. It was in running condition and I drove it 5 miles home.

I swapped it in and used my original closed system radiator and overfill bottle. I drilled 2 holes at 12 and 6 on the new T-stat and installed it. I then filled the overfill bottle and radiator with fresh water and a little bottle of Prestone flush. I also jacked up the rear end to tip the front end forward. I ran it a 5 times or so in 20 minute increments where I allowed it to fill the overflow to the tip, shut off the engine, and slowly removed the coolant sensor. I replaced the coolant sensor and then let it "burp" out into the overflow tank.

Problem is that I have done this over 5 times and if I let it run for more than 1 minute it just boils over and violently blows out the overflow bottle. If I shut it off it slowly boils out and pulls some coolant back down.

I even hooked the sensor back up and it isn't even halfway up the temp gauge. The radiator is even pretty cool, I can lay my hands on it with no issues. Hoses are warm, so it seems that coolant is flowing through. I have a large fan in front of the radiator to keep things cool also.

Am I missing something here?

I don't have much respect for the 15 minute flushes. Try a radiator cleaning agent, the kind you run for 3-6 hours.

Is the pressure bottle cap sealing? If you don't have pressure on the coolant the boiling point is going to be lowered.

I run a Stant 10244 cap, from a 700 series Volvo 2.3 L pressure bottle. Seals better than OEM or standard aftermarket caps, lower profile so it doesn't hit the underside of the hood when the bottle expands, and has a higher pressure rating to raise the boiling point higher.

Don't forget that the pressure bottle shouldn't be more than 1/3 full WHEN COLD.

You could have air trapped, the closed system must be deliberately burped, sounds like you tried to do that, and you drilled the holes so that should be good.

Try a cap change and post up your results.

joe_peters said:

Is the pressure bottle cap sealing? If you don't have pressure on the coolant the boiling point is going to be lowered.

Click to expand...

I think you just found my problem. I always thought you burped coolant systems with the cap off so that's how I've been doing it. That makes sense that the water would quickly boil over without the cap on.

I will go ahead and pick up one of those caps as an upgrade whether I need it or not, sounds like a winner.

Thanks! I knew it was just me doing something dumb :yelclap:

I have taken it for several test drives and everytime it comes back the overflow is filled to the brim and it looked like it was about ready to pop.

When I slowly took the cap off it burped up several air bubbles. The last drive I took was about 10 minutes and it made it to just under the red zone on the temp gauge. After a few minutes I untwisted the cap a little and it just pounded out air bubbles for about 2 minutes straight.

Is this trapped air that is STILL in the engine? Am I missing something again? I figured it would all be out by now....

It really sounds like the thermostat isn't opening or the water pump isn't circulating the coolant. I'd probably change them out on general principal (if it were mine) and refill. While it's apart, garden hose the radiator to verify it is not blocked as well.

Thermostat was brand new, but that could very well be it. Could the water pump be tested any way?

Did you feel the radiator hoses to see if coolant is circulating?

Sounds like way too many air bubbles in coolant--test for combustion gasses in the cooling system.

Lower radiator hose was always pretty hot. Upper one was warm most of the time.

How do I test for combustion gases in the cooling system? Is that leaning towards a bad head gasket?

I also jacked up the rear end to tip the front end forward

lift the front end, not the rear.

There are at least two approaches to gettting air out of the system, raising the front or rear. I like the front better cause I live on a steep hill!

I try to fill everything before closing the system up. I will fill the radiator with the upper hose disconnected so I can see the coolant coming out of the t-stat housing. then button up the top hose. I also make sure the heater system is full as well. top off the radiator and overflow tank.

The other item you may want to check is the spring in the lower hose. If there isn't one, how do you know the hose is not collapsing when driving? Did you verify coolant flow in the top hose? It can be warm without flow. Activity in the overflow tank will not verify flow either. Does the heater work normally? That might be a good indicator.

Front end up--works for open systems with a cap on the radiator at the front of the vehicle.

Front end down--works for closed systems where you need to pull the temperature gauge sending unit from the rear of the head.

I didn't have a chance to try all your guys's suggestions tonight, I just had about 15 minutes to drive it 6 blocks and back. Same deal as before, crack the cap and it violenty boils out of the bottom of the overflow tank.

I checked over the hoses and radiator and found that the lower hose was very hot, I could barely touch it. The top hose was warm near the radiator end and extremely hot near the engine end. I was also able to touch the middle of the radiator and it wasn't too terribly hot, just warm.

Sort of sounds like it's not fully circulating the radiator, right? Why would the upper radiator hose be super hot on the engine side and slightly hot on the radiator side?

It sounds like you pulled or replaced the thermostat. Any chance you got it in backwards?

You know, that very well could be a possibility. I don't recall how I did install it, I thought it was straightforward and didn't require much thought. Apparently it does

I think I may just pull off the t-stat housing and install it back without the t-stat to completely eliminate that as a possibility as a start

Make sure the bottle is over half full... Plus make sure you have the heater hoses on right..Don't ask me how i know this...My heater core went out so i ran mine right thru the bottle and back to the motor..In thru the top and out thru the bottom..
HTH..

Did a little work on it tonight. Pulled the t-stat completely out and blew out the radiator with the garden hose, seemed to have good waterflow to me.

I guess I don't understand the proper "burping" technique. From what I have heard I need to jack up the rear so the air goes to the back of the head where the coolant sensor is, right? Open the coolant sensor and fill the overflow tank until it spills out the coolant sensor hole. Put the coolant sensor back in and run it, right?

Then what? After the coolant jug starts getting full I have been cracking the coolant sensor open to allow the air to escape from the back of the head. I also crack the coolant overflow lid to allow pressure to "push" the air out of the back of the head. Am I doing this right? Do I need to continue to do it?

Thanks for all the help, I'm slowly getting to the point of understanding the closed coolant system concept....I think...

If you have a closed OEM system, as you posted earlier, you don't have an overflow, you have a pressure bottle mounted on the passenger's side firewall.

Terminology is important as it gets everyone on the same page.

Ok, A**uming you have the OEM 89 closed system, radiator w/o cap, pressure bottle on firewall. You want to "burp" the air out you need to park it NOSE DOWN, putting the temperature gauge sensor as high as possible in relation to the radiator, thermostat, and most of the rest of the engine. Once you have established that relationship, pull the temperature gauge/idiot light sender from the head, driver's side rear. Be careful not to break it, and set it aside. Now, at the pressure bottle mounted on the firewall start adding coolant. In theory, and hopefully in practice, the coolant entering the pressure bottle (which is slightly higher than the sender port in the head) will push the coolant through the system and force the nasty air bubbles out of the sender port. Once you have a good flow of coolant reinstall the sending unit. That should take care of it. Those two holes you drilled in the thermostat flange, if done correctly, will assist in passing coolant and air through the engine.

Now, the pressure bottle should be about 1/3 full when COLD. This will leave room for the expanded hot coolant to fill. Unlike an open system where coolant leaves the system and is stored in the recovery/overflow reservoir, coolant in the closed system remains in the system under pressure.

Good luck.

Yes, I have a OEM 89' closed system, radiator w/o cap, and pressure bottle on firewall.

I think the only way I may have deviated from the instructions is that I put the coolant sensor back in the head immediately after the coolant flowed through the top. Should I let it run out about 10 seconds or so? My pressure bottle was also between 1/3 and 1/2 full so I need to remove some there also.

I have had a few water pumps fail, all of them either bearing or seal wise, until a year ago I had never seen one with the vanes on the impeller gone. This was on a 98 and we would top of the radiator and use one of those big funnels that attaches to the radiator filler, after about 3 minutes it would start boiling over. The radiator was new, cap new, belt new and adjusted correctly, pulled the water pump and the vanes were non existent. The water in my area is very hard and does a number on copper pipes, I have always used distilled water in my cooling systems so I never ran into it. Replaced the water pump and all was well.

Tried again last night. Jacked the rear end waay up, pull the coolant sensor, and kept filling with water for about 20 seconds while it poured out of the back of the head. Stuck the sensor back in and tightened the coolant jug cap down. I let it idle and even wrapped it up to about 2-3k rpms a few times to add some flow and heat. Went at least 15 minutes with the temps slowly climbing just slightly over 220 with the primary electric cooling fan whirring away. Coolant jug kept near the top but never filled to the brim, a first since I swapped engines

I don't feel so bad about driving it now, time to slap the header panel back on and give it a real test drive

Is it advised to jack up the rear one more time and go through the burping motions again?