overheating after flush and new coolant
 

On Monday I drove about 20 miles with my AC on around 6pm on the 101 north from the 60. At Indian School my dummy light temp sensor kicked on, so I pulled over to the right and flipped off the AC and on the heater. The light went off but at Frank Lloyd Wright I got off the 101 and sat at the light until green. I still had the AC off and the dummy light went on again. There's a little gas station there so I pulled off and let it sit for about 10 minutes. I know the 4.0's notoriously run hot, but it wasn't even 100 yet and I am running into issues. On Tuesday I emptied the coolant and used flush. I followed the directions, got a new rad cap and put in new coolant. I have replaced my water pump, thermostat and radiator about 6 years ago but have only put 5000 miles on it since, so I don't drive it much. With it all apart I found what looked like rust as it was brown and gunky, but a mechanic friend said its probably head/cylinder additive. So on Tuesday I found the same gunky goop. Is this the reason my xj is overheating? What other things can I do to cool this down especially when its hot every day?
Thanks.

I'd be a little worried if there was head/cylinder additive in your coolant and you're now getting overheating issues.

I would grab some test tools and check your engine.

That said, you could need to flush the system a little more thoroughly. The standard flush kit is fine for routine flushing, but if you suspect there's crud in the radiator (and it doesn't take much to block those little passages) you need to run a hose top to bottom and bottom to top (and probably remove the radiator to do it).

Did you ever by pass the heater control valve? I think 96 was the last year they used it. So living in AZ and not driving it much, the fluid sitting in the heater core could turn brown and gunky. When you flush it make sure the heat is on to try and clean out the heater core if it has not been by passed

If the engine has already been cooked a couple of times I would perform a cursory check for combustion gases in the cooling system before replacing a whole bunch of parts.

I only noticed it when I was driving for a long period of time and not in stop and go traffic. It does fine when I go to the store or run errands around and near my house. But it was particularly hot on that Monday and I'm sure it wasn't helping. I have driven it down to Tucson and back (I drive for my job) with no issues for overheating...

In my owners manual, it says when doing a flush that you should remove the engine block drain plugs. Mine is a 4.0 and it locates this plug right at the collector of the exhaust. Does everyone remove these when doing a flush? Are they easy to remove and once its removed will it help me with my problem?

Yes I did. The instructions on the bottle said to turn the engine over and let it run for 10 minutes with the heater on and to do it twice.

What would be a good way to do a cursory check for combustion gasses?

Your local parts retailer should sell test kits. You can also grab a loaner tool block tester and some test fluid.

CM test
 

I got a Lislie test kit from Oriely auto parts...easy test....do it on two different occasions when engine warm...

It's going to work much harder with in-town/city driving as you don't have that same constant airflow rate going through your radiator, etc. as you do on an open road. Also make sure your fans are both working correctly and coming on when they are supposed to.

In my owners manual, it says when doing a flush that you should remove the engine block drain plugs. Mine is a 4.0 and it locates this plug right at the collector of the exhaust. Does everyone remove these when doing a flush? Are they easy to remove and once its removed will it help me with my problem?[/QUOTE]

Has anyone had any success by removing the engine block drain plugs? Is it hard to do?

Thanks for being Captain Obvious here. Re-read what I said about the driving I was experiencing.

Bump!

Your cooling system could very well have rust in it if overheated or neglected. Common problem with the cast iron block. I have a '98 that was not overheating but had a very dirty and neglected cooling system from the PO. Light brown sludge in radiator filler neck and in the overflow reservoir. Took multiple hose flushes as well as drain and fills with just distilled water before it came clean. Flush the heater core separate from the radiator and block. I did not attempt to remove the block drain plugs.