Looking for a second opinion on my overheating troubles

I have a 1990 Renix 4.0 (w/ AC).

For the last few weeks (ever since I installed the proper coolant temperature sending unit to go with the gauge I installed almost a year ago), my XJ's coolant temp has gotten up near 250 at least once per day. There's one stretch of road, mostly flat actually, where it's guaranteed to happen. Every day on my way to school, I now have to budget time to pull over and let it cool before continuing.

I checked the coolant, and found that it was a little low. I added coolant , and it didn't seem to help. Tonight I flushed the coolant (I put almost four gallons of distilled water through the system) until it drained clear, and then refilled with 50/50 distilled water and antifreeze. It didn't help either.

I've noticed some things that I think contribute to my overheating:

1. I have a header now (painted Pacesetter). I don't know how directly that would contribute to my overheating problem, but I'm sure it can't help.

2. My coolant overflow bottle is cracked, and the cap doesn't seem to be sealing (I could hear it hissing when the engine was running). That's getting replaced for sure.

3. I have never noticed my auxiliary electrical fan running. It's supposed to come on automatically when the A/C turns on, right? My A/C doesn't work, but I expected the fan to kick on when I switched on 'A/C max'. No dice.

4. I believe the radiator is the original 1990 unit, with close to 175,000 miles on it. I'm no mechanic, but it doesn't look like it's in the best of health. Here's a crappy cell phone picture to show how corroded the hard line is, and how the fins are falling off and just plain old-looking:


Given what I've just posted above, do I need to replace my radiator? I know I probably should, but the engine it cools is on its last legs, and I'd prefer to just nurse it until I can afford to replace it all if I can.

the pic and description of the radiator pretty much condemns it right there. the bottle and cap not holding pressure will also make the renix very unhappy. hopefully 5-90 will probably chime in here as well.

First thing is the bottle is not a overflow on that year, if it's cracked the system will not stay cool.

I should add that you must use the same pressure bottle, a generic overflow bottle will not work is must hold pressure on your closed system.

yep, a pressurized bottle that's not will cause cooling issues. replace the cap and bottle at the very least. make sure you get ALL the air out of the system, and see how it does after that. i would strongly recommend a new bottle, cap, and radiator all at the same time.

Yep that "coolant overflow bottle" is actually called an "expansion tank"(I think) on these "closed" cooling systems.IT MUST HOLD PRESSURE! If not you WILL overheat!Same exact thing happened on my '90 xj w/4.0.(same ride as yours).These cooling systems are just barely adequate to start with,get one little weak link and they will fail you! I just chucked the whole "closed" POS system and converted to '91('92?) and later open style system.This is what I HIGHLY recommend for when you finally decide to fix her up right.You will need a radiator and heater control valve from the later XJ's to make the swap.Search these forums for all the details.Also you need to get that AUX. fan running.Even the upgraded cooling system wont keep you cool idling at a stoplight on a hot day(or even a lukewarm day) without it!Its probably the relay for the fan thats crapped out,I think its one of the relays on the DRIVERS side fender if I remember right(same thing also happened to me).Check the fan though too,it should spin pretty easy when you flick it with your finger and it shouldnt wobble horribly or anything when you rock it forward and back (indicating wasted motor bushings).I guess the windings in the motor could also be fried(doubtful).Anyway youre probably bright enough to fill in the blanks.Hope this helps!

PS:How do ya like that header?I have the same one,I think its excellent for the money considering the cost of the alternatives.

Closed systems are not bad at all, this one lasted 16 years.

Here are some write ups that work great, Good Luck
http://www.olypen.com/craigh/tech.htm

1) That "hard line" isn't for your cooling system at all - it's the refrigerant line to the condenser (that radiator-looking thing in front of your radiator.)

2) You're in about the right timeframe for the OEM RENIX radiator to go out on you - I've been informed by Jeep Techs, Jeep Parts Guys, and Jeep Service Writers that the RENIX radiators are commonly failing at 150-180kmiles. They also (all!) advised an aftermarket replacement (they don't make any money on me, which keeps them honest.)

3) Typically what happens is that the RENIX radiator gradually starts to clog, from the bottom up. I'd be willing to bet that if you took a non-contact IR thermometer, you'd note a temperature gradient going up along the core - getting warmer from bottom to top.

Replace with Modine or CSF (I've heard good reports from the field on CSF units from Dirk at DPG - but I'd already gotten Modines locally,) and you should be all right. I'd probably replace the pressure bottle while I was about it - you should be able to get a new bottle and cap from Morris 4x4 Center (www.morris4x4center.com) for about $30 - that's where I get them.

If you haven't flushed your radiator in the last year, do so now using Prestone 7-hour flush or the two-part flush (the flush is mostly oxalic acid in powder form, the other "part" is a neutraliser) and then change your radiator. That way, you end up taking a lot of crud out with the radiator. That would be a good time to change ALL of your hoses as well, and I'd put your hose on the heater core tubes at the firewall and blow it out as well. Flush everything, then change the radiator and hoses - that way, you're not putting old crud into new parts (why ever would you want to do that?)

No reason at all to convert to the later "closed" system - there's nothing at all wrong with RENIX. I've got five RENIX rigs - one was converted before I bought it, and I'll probably convert it back (since it runs warmer than the rest...)

5-90

5-90 said:

No reason at all to convert to the later "closed" system - there's nothing at all wrong with RENIX. I've got five RENIX rigs - one was converted before I bought it, and I'll probably convert it back (since it runs warmer than the rest...)

5-90

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X2! People (in general and other threads and forums) have multiple leaks, cracks and old radiatiors and blame the "POS" cooling system on a "POS" renix xj. Like 5-90 said, they are probably better than open by comparison.

I have been thinking about flushing the coolant system on my new project jeep but I am a little nervous. I have been told that that could cause more problems than it is worth. It is a 89 with a 4.0 and about 200,000 miles on it now. The coolant looks ok (not like new) but winter is coming and I do drive it on occasion. i am just afraid of leaks springing up. Also what do you folks think about engine flush ( the stuff you can put in the oil and clean out that system also )? Thanks!!

Don't be afraid to tackle the radiator replacement yourself. It is pretty straightforward. Took be about two hours total time.

Thanks for all the opinions, guys. I'm definitely replacing the pressure bottle, and will be tracing the wiring for that fan (how hard would it be to wire a manual switch to turn that one on?). I don't have $200 to drop on a new three-row radiator right now, though; I guess I'm just going to have to take it easy for a week or two.

5-90 said:

1) That "hard line" isn't for your cooling system at all - it's the refrigerant line to the condenser (that radiator-looking thing in front of your radiator.)

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So if I ditch the A/C, can I get rid of that whole thing (and hopefully get more airflow to the actual radiator then)? That'd be cool.

I got an OEM replacement for my closed system for $130 shipped from radiatorbarn.com It works great for me, and since i know it works so well now, im glad i didnt dump 200 on a 3 core.

Mambeu said:

Thanks for all the opinions, guys. I'm definitely replacing the pressure bottle, and will be tracing the wiring for that fan (how hard would it be to wire a manual switch to turn that one on?). I don't have $200 to drop on a new three-row radiator right now, though; I guess I'm just going to have to take it easy for a week or two.


So if I ditch the A/C, can I get rid of that whole thing (and hopefully get more airflow to the actual radiator then)? That'd be cool.

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Ayuh - but you'll either need to leave the compressor in place, or find an idler pully and bracket (it's what Jeep did when they didn't equip a 4.0 with aircon - so they could use the same belt either way.) They can be found - and if you find two, grab the other one and let me know what it cost you.

The idler will probably need a new bearing - Timken #203FF, as I recall.

5-90

5-90 said:

Ayuh - but you'll either need to leave the compressor in place, or find an idler pully and bracket (it's what Jeep did when they didn't equip a 4.0 with aircon - so they could use the same belt either way.) They can be found - and if you find two, grab the other one and let me know what it cost you.

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Well, I'd keep the compressor itself for onboard air, but everything else A/C-related would get tossed.

Mambeu said:

Well, I'd keep the compressor itself for onboard air, but everything else A/C-related would get tossed.

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That should be fine - but yeah, everything else can go.

Note that things like the condenser are copper - and can therefore be sold to a scrap metal vendor. My scrap metal programme helps to fund other projects (copper, brass, bronze, aluminum, and CRES are all targets - mild steel gets picked up by the city. At a penny a pound, steel isn't worth the fuel for me to haul it in! Between scrap metal and CRV, I usually come up with a few extra bucks just when I need it...)

5-90

My AC condenser "fins" were clogged with all kinds of debris. Being as the AC doesn't work and the fins were corroded beyond help I just started pulling them out, got most of them out, that opened a lot of radiator area to cooling that was previously blocked.

dizzymac said:

My AC condenser "fins" were clogged with all kinds of debris. Being as the AC doesn't work and the fins were corroded beyond help I just started pulling them out, got most of them out, that opened a lot of radiator area to cooling that was previously blocked.

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Now that's a good idea!

Okay,okay maybe I was a little harsh with the POS statement regarding the closed setup!I admit when I changed my coolant tank(or whatever) on my closed setup that it worked okay for a while,but with all those pre-fab metal/rubber hoses and failure waiting to happen plastic pressure tank(or whatever) I figure why not go with the much cleaner(neater) late setup?Obviously Chrysler thought so too.I just fail to see how having a big plastic pressurized tank,that will harden and crack and eventually leak can be any benefit!I have nothing against the RENIX electronics I think they work fine.The whole rest of the Jeep works fine.One of the overall best damned vehicles I've ever owned actually!Anyway I would suggest replacing just the bottle(or whatever) until you can do it all right!And running a manual switch for that fan should be no trick at all.You could wire a manual switch in place of the temp. switch in the radiator and keep the relay or just wire it directly to battery power with a high-amp switch.Whichever you prefer.I did the temp switch method on my MJ(oh yeah did I mention my MJ) 'cause the radiator conversion deleted the original temp switch.(yeah converted the MJ too).So I just cut the plug off the temp switch and wired a manual switch in its place.It was just conveinient.By the way the CSF radiator SUCKS,put that one in the XJ and it blew-out tubes in under a year.Maybe it was just a bad one I dont know,but the GDI rad. I put in the MJ has about five years on it now with no trouble.

Chrysler thought so too.

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Only because it was cheaper to build.

Think about it, Open systems breath air and dust in and out on every heat/cool cycle.
With a closed system, nothing enters the system once filled and closed, you do have to keep the open systems filled, the closed never uses any more water once filled.