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TJ 4.0L 1999- Rusty Coolant & Hot on Highway

6K views 6 replies 7 participants last post by  Drivnchaos 
#1 ·
I have enjoyed owning my TJ for the past three years. I was told it had a brand new radiator by " the man".But suddenly it started regularly running on or just right of the 210 mark instead of just left. I also noticed it ran Hot going highway speeds.

So i flushed it with water and noticed a dark brown red collor in my coolant. I continued to flush&run several time and the collor got lighter and less but different disapear. So i got a chemical "3 day flush" it was sometype of acidic syrum i believe. Anyways i kept it in and ran it for 4 days, and extra one. When flushed extra material came out of flush. But a flush with water proved the collor to still be coming out.

Ive changed my water pump, thermostat, heater core( witch leaked and had "Rusty" deposits in it). It still runs at 210 and just right og when HW. Please help me :(
 
#3 ·
Dead on at 210 is the correct operating temp. Also, the needle moving a hair right or left of the "1" in the 210 indication at idle or highway speed, and depending on driving conditions is no big deal and I would consider it normal.

FWIW, my 99 TJ also had rusty coolant when I first got it because the prior owner did not change it often enough. You were right to flush it. It took me a couple good flushes, and then I changed coolant (not fully, just a good radiator drain-out) at 3 month intervals for half a year to further clear out the system over time, and now my coolant is the correct green color and has been so for the past two years.

The cast iron block (If I recall correctly) will corrode a bit on the inside if the coolant is left extremely long times without changing it out. I saw this in my engine when I changed out my water pump. That contributes to the rusty color you are seeing but as far as my experience is not fatal to the engine if caught early enough. It will dissipate over time with flushing and coolant changes. Just stay on top of it with regular coolant changes which will keep the proper corrosion inhibitors in the coolant functioning as they should.
 
#4 ·
as said 210 is normal operating temperature. problem is the gauge points at 210 when the actual coolant temp is anywhere between 185-235. that's why I suggest using an OBDII scanner/device of some sort to read coolant temps in real time. then you actually know whats going on.

next, what water pump, thermostat and heater core did you install? Mopar is the only way to go for the pump and heater core. A Stant Thermostat from NAPA is a good way to go. You do NOT want a failsafe thermostat.

lastly, how are you flushing? draining from the radiator petcock? if so, that doesn't get the rusty chunks out. gotta pull the lower radiator hose off and let it pour out. Also when using water to fill, always use distilled water.

If you want to thoroughly flush a dirty rusty cooling system, you'll need to flush with a garden hose kit for probably an hour or more, and go through several gallons of distilled water over several days (maybe even weeks or months), before you're done & get clean water. Once things run clean, then its a good time to install your new radiator, heater core, water pump,thermostat, hoses, etc...and reinstall the proper 50/50 Zerex G05 HOAT coolant & distilled water mix.
 
#5 ·
Had the same issue when I purchase my used 02 Wrangler Sport. Turned out to be a rusted out freeze plug that someone had tried to seal with high temp calk. I suspect that the PO did not perform proper maintenance on the cooling system. After the new freeze plug, new water pump and radiator service and coolant, I still had rust in the system. I ran with this setup for about 2 months, then the stock radiator cracked on the top (cheap pressed plastic top).

My next step was to replace the radiator with an aluminum one from LedFoot Racing and a new thermostat, new overflow tank and new hoses. I used a flush kit with chemicals and water hose to flush the system completely several times, then finished with several gallons of distilled water. Can't say that the water was coming out clear, but it was a lot better color after all those flushes and changing all the components.

The engine block is the least of your worries, as well as the freeze plugs if you have a newer model. The water pump, if after market cheappy may be concern, but most are okay. At minimum, do a complete flush and change the hoses, as some of the rust will stick to the inside. Finish the last flush with distilled water. Fill, start, idle to temp, turn off, cool, flush, rinse, repeat. The garden hose kit that allows the complete flush can be picked up at most box auto stores.

Good luck!
 
#7 ·
The best way I have found to completely flush the cooling system is to disconnect the heater hose from the thermostat housing, then put a hose in the radiator neck and let it flow from the heater hose nipple until the water runs clear. Then do the reverse, water hose to the heater hose nipple until the water coming out of the radiator neck runs clean. Then I put the water hose to the heater hose and let it flush the heater core out through the radiator and thermostat housing, or disconnect the other heater hose and let it flow out that way. This does put a lot of water in the system so when filling back up with coolant, I just leave the heater hose off the t-stat housing and start dumping the coolant in the radiator until the water turns green coming out if the heater hose nipple, then put the heater hose on. I do use a no spill funnel which directly connects to the radiator neck so the coolant is a constant input pushing out all the water.
 
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