Closed system cooling issues - Should my pressure bottle be leaking?

Alright, a few questions that I need clarification on if anyone knows or can help. (Yes, I searched, but I'm still in the dark on some stuff here).

My 87 Laredo (4.0) always seemed like it ran a little hot. It's never overheated though even driving up mountain passes in summer, etc. However, the temp guage seems like it's really screwed up. It never goes below 210, even when I shut the jeep off, and sometimes when I start it cold, it pegs all the way to the right, or very close. Sometimes it just sits above 210 like it should, sometimes higher depending on the outside temp. Anyway, it's so unpredictable that I've never really paid close attention to the guage as being accurate.

Anyway, today I was waiting for a friend and sat with the jeep idling for about 15 minutes, no A/C running, it was fairly cool out (the sun was behind the mountains, but still light out). I wasn't paying attention to the gauge as normal, but I noticed that I had steam escaping from the right side of the hood where the coolant bottle sits. Looked at the guage and it's in the middle of the red. Uh-oh.. So I opened the hood up, and there's a hissing noise and coolant running all over the right side inside of the fender, and a small puddle on the ground. I did note that the aux. fan was running, so it didn't overheat because of that.

So, first off what's the deal with the temp guage? Even on a cold start, sometimes it goes into the red (immediately), sometimes it pegs all the way right (to the little stopper), but it always starts off at 210 (right in the middle), it doesn't start off cold and slowly rise, even when the jeep is off the temp guage reads 210. Do I have air in the system that's screwing with the sender, or is the sender just fried, or should I just completely disregard the silly thing?

Second, does the coolant bottle have an overflow of some type, or is mine cracked? I can't see any kind of cracks, and the cap did not blow off, it just bubbled coolant out from somewhere in the back. Cracked? Replace it? Shouldn't the cap blow off before the bottle cracks?

Finally, where do I start with the overheating? Some have pointed to the fan clutch as being the culprit for an idling overheat? I can spin the fan clutch freely with the motor off, just a little bit of resistance. Sound bad? Tomorrow I'm going to look into doing a system flush, but I don't want to mess with it until I fix the coolant bottle (if it needs replacing), as the coolant will just boil out again. After that, if the flush doesn't fix, assuming the clutch is good (or replaced), and the coolant bottle holds pressure, then the next step would probably be the radiator, right?

Well, the pressure bottle shouldn't be leaking normally. It is a kind of pressure cap, though. Once pressure builds high enough, it iwll seep through the slots in the threads (you can see them on the cap, like on most soda bottles). But if it did leak at all, it would not be from the back, it would be from the cap. Once the system has a leak, you lose the advantage of pressurization. So your coolant heats hotter, faster. I would bet it is cracked. With pressure relieved, the crack probably seals itself to a visual inspection.

If the fan clutch is working, it should be very hard to turn by hand with the engine off and at a warm operating temp. Once the fluid (or spring) warms inside the clutch, it essentially locks the fan onto the shaft and increases airflow.

The radiator may very well be a problem. For one main reason. Your vehicle is not a spring chicken, and if the radiator is stock....it's past due in my book. Which would hold true for any component in the cooling system, actually.

Does your lower radiator hose have a spring inside it, to prevent collapse under a vacuum? It should, and that could be a problem as well. If the spring is absent or corroded away, coolant flow will be restricted. Which could arise from a faulty water pump, as well. And while we are pulling out all the stops, how old is the thermostat?

There's a fair amount of troubleshooting, and I know I am forgetting some pieces to the puzzle, but those are the things that I would check first.

As for the gauge acting wonky? No idea there. It could be related, or it could be a shot sending unit or grounding out somewhere.

-Rich

The thermostat is fairly new, I replaced it a while ago just for giggles. However, now that I look back on it... I remember that the replacement I got did not have the little hole in it like the stock one did. Is this hole absolutely critical? I've read somewhere that there is no way to get all the air out of the system without this hole... should I take it out and drill a little hole in there, or is this not as much of an issue?

Also, like you said, the radiator is suspect as well, but I want to try some other troubleshooting before I go and order one, as money is an issue right at the moment and I haven't been able to contact the previous owner (one previous owner) to see if he had ever replaced the radiator. I plan on doing a good flush first anyway to see if it helps at all with cooling.

Also, has anyone ever done away with the fan clutch and replaced it with one of those "flex fans" that flatten out at high rpm's but pull lots of air at idle? If I go by what Colorado_XJ says, then my fan clutch is definately toast, as I can spin the fan fairly easy with the motor off but hot. My dad has a few spares of these around and suggested possibly just putting one of those on. This a bad idea? OEM fan clutch is $50 on quadratec, flex fan is free if it works.

I've always been told not to run a flex fan in a off-road vehicle, because if you hit deep water, the fan can deflect into the radiator....not that I know anyone who this has happened to....but??

Justin

TNScrambler said:

I've always been told not to run a flex fan in a off-road vehicle, because if you hit deep water, the fan can deflect into the radiator....not that I know anyone who this has happened to....but??

Justin

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Well, I usually try to avoid deep water for other reasons, so I think unless someone else has a reason why this would be a bad idea, I might try it.

Easy ones first- go ahead and replace the radiator-cheap insurance- look around and find them for anywhere between $99 and $169. Get the 3 row heavy duty, or 4 row extreme- Modine is supposedly makeing one called "heat buster"-havent seen it yet.If you want to switch over to the open system, nows the time. You`ll get a real radiator cap, and loose the bottle-bottles get expensive after you replace them a dozen times in the lifetime of the vehicle. They all crack, usually on the bottom where you cant see- PS: if the bottle ever blows and leaves you completely stranded, pop the nipple off the bottom and join the two hoses for a quicky escape to the dealer for a new bottle-

when you get a chance, or start tinkering, burp the system- do a search for burping the 4.0- it involves removeing the sender on the top of the block so the air can get out- air trapped in the top when you play with the radiator system causes hot spots that screw with the senders reading, and can overheat the engine- replace the sender anyway, cheap insurance again.

when thats all said and done, you might wish to put in a switch to activate the relay for the aux fan- that way you can switch it on when you want to, not when the secondary sensor or AC tells it to. Very usefull for keeping it from getting hot, then cooling-

If your radiator is the original, it is long past the point of needing replacement. I take good care of my vehicles and my OEM radiator on the '88 lasted barely more than 10 years before springing a leak. It was about 75% plugged internally at that time.

Replace your temp sensor for the gauge. It's located on the rear corner of the head, driver's side. A new one should cost about $10.

Before doing any repairs cept for the leaking bottle drain the system, refill with water and add a bottle of prestone 7 hour flush. Follow the directions, THEN install the prestone back flush kit in the heater hose. Once thats done and back flushed replace the hoses with new ones. Keep the old heater hose with the T fitting for the next time if you want. Personally I put new hoses in about every 5 years or so. This will remove and clean the engine block of crud and with you replacing the radiator will tie in nicely with a cooling system overhaul. Remember to turn on the heater during that time so the heater core gets the cleaner too.
When removing those old original hoses from the heater core don't try to pull them off, instead with an exacto knife slice them lengthwise then peel them off. It is no fun to break one of the fittings off. The factory heater hoses come with clamps on them and the factory radiator hoses come with the the spring and protective covers, plus they FIT and have the correct bends. Use distilled water when refilling. This is the one time I would use a shop to hookup a coolant flush system to pull all the old tap water out you used for the back flush before refilling with 50/50 mix of coolant and distilled water.
From what I have read here on the closed systems the plastic mixing valve is an easy breaking piece due to age. I understand the replacment, aftermarket, is made of metal not plastic so it might be worthwhile to investigate that and for some reason $15 or $30 comes to mind from AA.

If you plan on keeping it get the part number and parts list from eagle for the summit aluminum replacement tank instead of another plastic one.

Well, it's a new day and I'm not so mad at the jeep now, so I'm gonna work on it today. I'm gonna start with the basics first... new coolant bottle and a good flush and burp of the system. My fan clutch definately needs replacing, but if the flex fan will fit I'm going to try that and report back results.

Also, what's involved in replacing that lower radiator hose? Mine feels really squishy and thin, not sure if there's a spring inside or not (can't feel anything like that). Am I going to curse myself for ever even trying to replace it, or is it fairly easy to get at? My upper hose and heater hose look much better, almost think they've been replaced at some point, so I'm going to leave those alone.

Lower hose, two clamps and a new hose, not a big deal. You are going to drain the system and flush it anyways. Just make sure the new one has a spring in it to keep it from being sucked flat and restricting coolant to the pump. Like I said before, I like the OEM ones, they fit, have the spring and even have the anti-chafing sleeve on the outside of them already.
I'd do the 7 hour flush after you get the new bottle in then do all the other stuff. At least it will get the inside of the motor clean. Also to cut down on build up in the engine internals you should remove and clean all your grounds. This will reduce the electrostatic charge that will build up in the coolant and act like a plating bath, depositing all the minerals from the coolant water inside the block and radiator which poor grounds will accelerate.

As long as you won't be doing water crossing you'll be fine with the flex fan, and it will probably pull more air than the OEM solid fan. You'll need a spacer to make up the thickness of the clutch, though, or the fan will sit behind the shroud. I think the spacer is 2" thick but measure the clutch. Spacers should be available at Pep Boys or a local speed shop.