xjallseasons

Hey 5-90, what are your thoughts on a 96 xj non-renix cooling system? Reason for my question is that this past week I blew my top rad hose from over heating. When I replaced with "new" parts the cooling system 2 years back, I flushed and reflushed along with 50/50 peak coolant. Although I did not buy a fan clutch everything else was new. Since it is NOT a daily driver and I have only put 9000 miles on it in 5 years, I havent been too concerned about it over heating. I do have an SE so it has the dummy/idiot gauges and I cannot see how close I am getting to over hearting. When it blew its lid, brown chunky coolant went everywhere which I refilled and got home with no problems. I had the AC running at the time and it was about 106 outside. I am not absolutely certain that my efan was working but it is new and I have seen it go on.
Any suggestions would be helpful.

djb383

How does coolant temp shoot up at start-up? Why would air be much hotter than coolant? Coolant flows thru the head like water thru a fire hose the moment the motor starts.....fast flowing water enters the rear of the head from the rear of the block. Sounds like the cooling system was improperly filled.......just because the rad appears full when re-filling doesn't mean the block/head r full. It's got to be filled very slowly and once the rad is full the motor should be idled with the rad cap off and keeping the rad full while idling.

cruiser54

I believe that with the cap OFF on a Renix system it will bleed just fine.

djb383

I'd bet either closed or open systems will bleed just fine when properly filled and the motor is idled with either type cap off.

cruiser54

Agreed.

SuperRA

The temp rises into the red zone. Not particularly fast, but it gets there when it shouldn't have. This is my theory. The air is NOT hotter than the coolant, but the absence of coolant keeps the sender from reading properly. The heat conducted from the metal head (which is not being cooled by coolant) gets hotter than it should. Thus the higher readings on the gauge. Also from what I recall when I had the head off, that there are coolant passages from block to the head along the whole length of the engine, not just the rear. Why do you believe the water pump pushes water all the way back instead of taking the path of least resistance? Come to think of it, a short cutting flow pattern like that might even force the air pocket back even if the engine is sloping up towards the front.
This is a renix closed system so there is no filling of the radiator, just the coolant bottle (which was left uncapped during warm up). If that's improper, then I don't see any other way that would be.. (except the bleeding procedure) LOL. Maybe I didn't wait long enough for the air to eventually make it's way out, but it was longer than I wanted to wait. Why wait for it when there's a simple procedure to remove it and be done?

Now you may not have needed to do this and that fine. I'm just giving feedback of my own experiences. It may help others, it may not, but it certainly doesn't cause any harm. I don't see why it's bothering you so much.

This works fine with all my other cars. It just didn't work for my XJ this time.

djb383

Doesn't the head gasket cover the holes in the block except for the large holes in the back of the block/head? I can see a closed system needing to be filled very slowly, slower than filling an open system maybe. I'm thinking it was filled so fast that there wasn't enough coolant in the block to even cover the water pump impeller. I just don't see how air can remain at the low rear when air naturally rises to the high front......unless the block was actually very low on coolant but thought it was full.

SuperRA

That could be the case. I don't remember what the head gasket looks like. Well I only had a theory. I don't know what's actually going on. I agree it doesn't make sense for air to stay in the low rear (and still somewhat believe it too) but it wasn't working that time and I just wanted it fixed so I tried all the tricks. I guess what's important is that it's working fine now.

djb383

All kinds of what ifs/particulars pertaining to your situation. Was the nose possibly slightly lower than the rear and not noticed when the initial, maybe too fast, re-fill was done? Look at those skinny hoses on the bottle that coolant must pass thru to properly fill the block, the head, the radiator and the large rad hoses, the heater core, etc. Being impatient, not wanting to wait any longer, could easily have lead to not enough coolant in the system.......as in maybe +/-1 1/2 gallons too little coolant which is probably not enough coolant in the block for the water pump to push up into the head. If the cooling system is only half full with coolant then the other half is air and an overheat will likely occur......but a 1/2 full cooling system is not a "burping" issue.......it's a low coolant issue due to improper filling of the cooling system. If u don't remember about the head gasket, maybe there r some other particulars pertaining to your situation at that time that have been forgotten as well.

Again, if the cooling system has been properly filled, and that would include the vehicle being on level ground (certainly not nose down), only a very small amount of air will be trapped in various nooks and crannies and that small amount of air will be forced to the closed system bottle for collection by coolant flow when the motor is started.

I've got an idea for a new thread.......it would be titled, "How do u burp a 1/2 empty cooling system?" What do yall think.....any potential there?

5-90

Close. Apparently, it's the lack of hot liquid coolant (due to a pocket of accumulated gas) that screws with the thermostat's ability to sense the coolant and open that causes the overheats. It doesn't make as much sense as I'd like it to, but the idea has some small merit.

(The hole in the theory is that the gas pocket will increase in temperature as well, and the thermostat should sense that...)

djb383

Yes, a automotive thermostat will open/close normally in either air or a liquid, at it's temp rating.

SuperRA

It wasn't 1/2 filled. I didn't add much more that a cup or two. The head gasket was 6 yrs ago. The coolant filling was months ago...

It's done. That's how it did it and it works now.

SuperRA

Well, air is an excellent insulator. Especially stagnant air like the air pockets in fiberglass insulation (the reason fg insulation works) and double pane windows etc. So the air wouldn't transfer heat nearly as efficiently as the coolant does. So the thermostat wouldn't react as fast as it should. (If your talking about the thermostat. I was talking about the sender. Same phenomenon)