Engine cooling problem, questions and theories abound

[Poyndexter]

This is a repost of a thread I created at another forum I visit, I'll post it here in edited form.

Okay, I'm going to try and make this concise and to the point.

I drive a '98 Jeep Cherokee Sport. It currently has 101k miles on the odometer.

About 9 months ago it started overheating. I discovered that the radiator, while disgustingly dirty, was in tact (no holes). I bought a flush kit and flushed the radiator out, adding new coolant/water. This seemed to curb the problem for a few months, maybe 3 or 4.

Over the course of a week, I noticed the average temperature slowly creeping up. One hot day after work (and 100 or so miles on the Jeep), the overflow hose leading from the radiator cap to the overflow tank blew off. The entire contents of my radiator spewed onto my windshield. Before I could get off the highway and pulled over, it started knocking (and slowed dramatically, despite my mashing of the gas). It died in an intersection and I had to push it off the road.

Jump to later that night:

One tow truck, a blown head gasket/cracked head later, and I'm left with out a vehicle.

That was 3 months ago, I finally saved the money to get it fixed, and picked it up today.

Before I could get home, it started over heating again (I did manage to pull over immediately and let it cool off, thankfully). Now, this is not the mechanics fault, I only paid him to replace the head/head gasket (as I didn't have the money to have him go poking around my engine any longer).

I have been able to narrow it down to one common symptom, but the problem eludes me.

It seems to me, that after about 30 minutes or so of continuous running, it over heats. Every time, regardless of circumstance, or if it's actually been moving or just sitting.

The only thing I haven't actually replaced and/or looked at is the water pump. But before I go ripping into the engine (this is one repair I can actually do), I would like some feedback from you guys.

[edit]Let me also add, that recently the fan shroud cracked and fell apart (I am getting a new one today or tomorrow), and that the electric fan quit working a while back, but I hard wired it into a toggle switch inside the cab.

[one more edit] I plan on getting a new relay and wire for the electric fan today. So those two problems should be taken care of fairly quickly. But I still don't think that they would make it spike to 260+ after 30 minutes of idle or driving.

[fredjacksonsan]

First of all Poyndexter, Welcome to AF! Lots of good info and people here.

As far as your cooling problem, I'd suspect the radiator first. You said it was heavily gunked....and even though you flushed it, even a small amount of clogging can reduce the flow enough to cause a problem. My brother's truck had a very slight amount of corrosion on the inside of his radiator, it was fine in the winter but overheated in the summer. He replaced everything else in his cooling system, but it still overheated - until he replaced the radiator.

Your story sounds the same...overheating (in winter), flushed the radiator, then it was ok until summer rolled around. Now overheating again, since radiator's not working at full capacity.

Since it's taking 30 minutes to overheat, I'd think that your water pump and thermostat are ok, because if they were bad it would overheat much more quickly.

Check/Search this forum for overheating, there are several links about where to get a good radiator online.

[Poyndexter]

Well, to be quite honest, I was a little curious after flushing it last night.

Even though the water draining from the bottom plug and the water spewing out of the radiator cap hole were sparkling clear, there was still settled sediment in the radiator cap reservoir that looked curiously like rust laden water.

[fredjacksonsan]

Originally Posted by Poyndexter

Well, to be quite honest, I was a little curious after flushing it last night.

Even though the water draining from the bottom plug and the water spewing out of the radiator cap hole were sparkling clear, there was still settled sediment in the radiator cap reservoir that looked curiously like rust laden water.

There you go....so, somewhere in the system is corrosion, and it's probably the radiator. 8 years and 101K have taken their toll.

I've always changed my coolant every 18 months and not had a corrosion problem, even when I purchased a used vehicle. I'd bet that when you did the flush several months ago, the coolant was brown.

[Poyndexter]

Originally Posted by fredjacksonsan

There you go....so, somewhere in the system is corrosion, and it's probably the radiator. 8 years and 101K have taken their toll.

I've always changed my coolant every 18 months and not had a corrosion problem, even when I purchased a used vehicle. I'd bet that when you did the flush several months ago, the coolant was brown.

It was brown to the point that it was almost black, the same crap that I flushed out last night. But really, I attributed that to the blown head gasket and the mixing of oil/water.

I bought this Jeep at 75k miles, and it was NOT taken care of. I've done quite a few basic repairs since I bought it, that were never done before (like spark plugs and wires, some of the wires were completely corroded off the plugs).

Also, a much belated thanks for the hospitality. I'm glad to be here, where people seem knowledgeable, yet friendly.

[fredjacksonsan]

You're welcome -- and when doing the replacement, don't forget to run water, both ways, through your heater core, which is another place corrosion can set in.

[Poyndexter]

Okay, I've talked to the mechanic (who has known my family for 40+ years, so I trust his judgement as well). He has also concurred with the radiator diagnosis. He gave me the number to his parts dealer, and for 88 bucks I'm picking up an OEM. They're mailing it to his shop and it will be there tomorrow, all I have to do now is pick it up and put it in. Thanks for the advice.

[fredjacksonsan]

Right on...(damn, hope we're all correct!)

[Po Pilot]

While you are at it - change out the mechanical clutch for the fan as well - cheap insurance!

[Poyndexter]

I don't want to be too preemptive, but I want to dance around the Jeep as we speak.

The radiator that I thought was intact was infact, a big piece of crap. The very bottom and right sides, were blocked in a way, that without taking the radiator out, you would have never saw the holes.

There were 4 spots that I could literally see my buddy on the other side.

The fan shroud was cracked out of the box, unfortunately (I'm taking it back tomorrow to get another one, but that means I have to remove the freakin' radiator again, at least in part).

Thanks for the help, I'll definitely be sticking around these forums. Not only because I have more issues that need to be resolved at a later date , but this is a good community you folks have going here.