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Overheating on the highway only. What could it be??
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Overheating on the highway only. What could it be??
Another XJ owner with an overheating issue here....
Below is a detailed history of the problem, but TL/DR: my cooling system cannot shed the heat at highway speeds only
Jeep was running great. Highway, traffic, no problem, but now I'm driving it in hotter temps for the first time. The temp sensor was replaced last year in August 2016. I bought the Jeep in December 2017. Coolant, thermostat and water pump was all last replaced October 2014 and radiator was last replaced in February 2011. 246,000 miles on the odometer, original motor.
I installed bigger tires, went from 28" to 31", and 2" lift installed.
I went for a test drive and drove it on the highway (temps in 70s) for 30 minutes and I noticed that the temp was higher than normal, but not overheating. When I pulled off the highway to get gas, the radiator cracked and all my coolant went everywhere. I wasn't looking at the temp gauge but I predict it may have jump up after getting off the highway. I had to get towed home.
Installed a new radiator, a 2-row copper core with plastic reservoirs. What coolant was left in the old radiator was no longer green but brown. I flushed out the engine through the thermostat housing and also flushed the heater core which was completely clogged (now it works).
Filled the system with water and a Preston additive to flush the system (not the kind with stop-leak in it). I also installed an auxiliary transmission oil cooler at this time and the trans oil does not go through the new radiator.
Went for a test drive (temps in 80s) and after maybe 20 minutes of interstate and freeway driving, the temp started to creep up again and when I pulled off the highway it boiled out of control and I could actually see the coolant boiling into the overflow tank. So I know the temp gauge/sensor isn't just playing games with me. And the electric fan was spinning too. Where I pulled off happened to be the 4x4 trail and I did the trail at slow rock-crawling speed in 4-low and the engine didn't get how at all. That tells me air flow is not the problem.
I drove home through the city and it was fine but the temp needle never dropped to the 210 mark or below.
When I drive around the city in never goes above the 210 mark.
I replaced the belt-driven fan clutch as I didn't notice a difference in resistance between it being hot and cold. I also flushed the old water out of the system with the additive for cleaning it out and this is what came out:
With 50/50 mix + Watter Wetter in the system and all the air bled out, I went for another test drive and experienced the exact same symptoms as before
I'm going to install a new water pump just to eliminate that as a potential problem, but I really don't think that's the issue as it cools just fine in the city and the heater also works really well now that I flushed it out.
Looking for ANY advice on how to improve my cooling system! I built this Jeep to go offroading in Colorado which is about 9 hours away and I will get it there no matter what even if it means putting in another motor.
That's where I'm at now.
Here's some ideas:
remove the AC condensor that's in front of the radiator to block less air flow. I don't use the AC as it doesn't blow cold and I'd rather the motor stay cool than me.
Hood vents.. although I don't think air flow is the problem.
Raise the hood to allow air to flow out the back. Will look dorky but I'm not too concerned about that.
Modify the air deflector that's below the front bumper to direct more airflow into the engine bay. Remove it completely? What's it good for anyways???
High flow electric fans.
What would YOU do if this was your Jeep???
Last edited by mannydantyla; 05-23-2017 at 02:59 PM.
Is that the new radiator? A lot of the fins look bent.
Do a compression test of the engine.
What year is your Jeep?
No that's the AC compressor. I blew all the bugs out with compressed air too but not much I can do about the bent fins except through out the whole thing and attach the oil cooler to the radiator instead
1997 XJ, auto trans, 4.0, etc.
I'll do the compression test soon. I haven't done it yet because... doesn't matter what compression I read there isn't anything I can do to raise it lol
Are you suggesting there could be a leak/crack in the head gasket? No signs of coolant in the oil or the exhaust. The engine runs great, pulls hard, can't even tell a difference with the bigger tires on except for at high speeds
Last edited by mannydantyla; 05-23-2017 at 04:55 PM.
Are you suggesting there could be a leak/crack in the head gasket?
If he's not, I am. You probably don't have a cracked head, given that you have a '97. But what you're describing sounds an awful lot like overheating from hot exhaust gas escaping into the cooling system through a blown head gasket. You can detect that with a combustion leak tester, which is basically a big fat syringe with fluid in it that changes color if there are exhaust gases present when you draw air up into it from your radiator filler neck. They range in price from $30 to $60, but you might be able to borrow one from Autozone if they stock those.
This actually makes sense that it happened after you put the bigger tires on it. Sometimes putting the engine under more stress will cause an existing leak to open up and make itself noticed.
If he's not, I am. You probably don't have a cracked head, given that you have a '97. But what you're describing sounds an awful lot like overheating from hot exhaust gas escaping into the cooling system through a blown head gasket. You can detect that with a combustion leak tester, which is basically a big fat syringe with fluid in it that changes color if there are exhaust gases present when you draw air up into it from your radiator filler neck. They range in price from $30 to $60, but you might be able to borrow one from Autozone if they stock those.
This actually makes sense that it happened after you put the bigger tires on it. Sometimes putting the engine under more stress will cause an existing leak to open up and make itself noticed.
Alright I think I remember seeing that as a loaner tool at Oreillys actually, I'll check it out
If the combustion leak test is negative or inconclusive, you should also do a leak down test to completely rule out the head gasket. Those kits I know you can borrow from the parts stores.
This morning I tried doing the "block test" (that's what Oreilly's calles it) to check for combustion gases in the coolant.
But it was a highly flawed test, at best, and at worst it was a completely worthless experiment that spilled coolant everywhere. The problem was that coolant was rising into the test tube and mixing with the test fluid.
You can also see that the coolant/fluid in the test tube is a little bit yellower/browner than the coolant showing in the filler neck of the radiator. The blue test fluid is supposed to turn yellow in the presence of combustion gases.
Then I started seeing little bubbles rise up through the coolant/fluid, so I took this short video:
The engine was warming up but was not yet fully warmed up and the electric fan had not spun at all. The coolant was replaced exactly one week ago, and I did my best to bleed air out of the system by idling the motor with the rad cap off and also squeezing the top radiator hose with the cap off.
What do you guys think?? Should I try again but with much of the coolant drained?
Those bubbles could just still be air coming out of system. Another thing tranny cooler should be mounted in front of belt driven fan for constant air flow. If you had a combustion leak bubbles would bee seen going into overflo bottle while running. When were upper and lower hoses last replaced ?
Time to replace hoses any way my bottom hose was actually sucking shut causing very similar to you highway issue. And there 3 1/2 years old. A new cap would also be advisable get auto parts to pressure check it b4 leaving. Then make sure thermostat open fill system then test drive .
What do you guys think?? Should I try again but with much of the coolant drained?
IIRC, I believe you're supposed to let the engine warm up with the cap off so that the thermostat opens and allows coolant to circulate. Check the directions on the tester. That top pic doesn't look like the coolant is flowing. The coolant level may drop when the thermostat opens. Be sure to let it warm up with the cap off, because you don't want to open a hot system that is under pressure.
I would definitely try again, because you can't be sure of anything from your first attempt. If the coolant level doesn't drop when it starts to circulate, draw some out and test again.
ETA: I looked up the instructions for one of the popular block testers, and it specifically says to siphon out enough fluid to give the tester a couple of inches of room to work without pulling in coolant. Just replace the coolant you removed when you're done.
Last edited by extrashaky; 05-24-2017 at 11:45 AM.
05-23-2017, 02:47 PM
Overheating on the highway only. What could it be??
