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Overheating 98 V6 ES

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Greetings — last time I had a question about this car overheating, it turned out that it was the reservoir tank — thanks for the help! This time, however, it looks like it's something else.

Here's the problem: driving around town, the car does fine. The temperature stays steady, unless and only unless I'm doing lots of stop/start driving due to traffic lights, which usually isn't a problem in the areas I drive city. It's when I'm out on the highway that things get wonky. Things move faster toward overheating when the AC is used, but I've seen this even when the AC isn't on.

I can drive for 20 miles at 60-70, and everything stays solid. It's then that the temperature begins to creep up. It will sometimes stay in the Safe Zone, but more often than not, I find that I have to turn the heat on full-bore and dump heat so that it will stay within acceptable limits. Once I get the temp down, I end up being able to drive a few miles without the AC on before it starts creeping up again.

So far I've had the temperature sensors replaced, coolant replaced, radiator fans replaced (and they run, so it isn't the relay), and another few odd jobs done. Coolant levels stay good, and I check oil regularly because I've got an oil pan seal to replace soon. My guess is that it's one of two things: the thermostat needs to be replaced (I don't think I've had that done lately), or the heating core / heating core line is clogged. Either way, I'm wondering if the coolant has nowhere to flow which means that the heat has nowhere to go. But I very well could be wrong.

I'd love to hear some serious (and perhaps experienced) suggestions as to where to go with this. Thanks!

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I think it's unlikely to be the heater core, since this is not intended to be used to keep the engine cool.

Thermostat is a cheap and easy thing to replace. The other two suspects are: blocked radiator (I mean internally blocked, though you could easily check whether it's externally blocked with bugs etc); corroded water pump fins (so it isn't pumping coolant). But those are more costly to replace.

I have forgotten the name of those infra red thermometer gun things that you can point at parts of the cooling system to read the temperature. But it might be worthwhile buying/renting/borrowing one to try to help diagnose the problem. If it shows cooler spots in part of the radiator, for example, that helps diagnose a blocked radiator.

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Thanks for reply. My mechanic is going to replace the thermostat next week, and we'll see if that does the trick. I'll also get one valve cover and oil pan gaskets replaced. The checkbook needs a workout, it seems. What I may also do, once these jobs are done, is do a radiator flush with a chemical treatment and see what, if anything, is loosened up / shaken out. I don't know if I want to go this far, but we'll see. Will update next week.

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Ok...here's an update.

I had the thermostat replaced; the oil pan gasket replaced (turns out it was only siliconed in place — I haven't had that touched since I bought the car 9 years ago (shudder); the coolant overflow bottle (it was leaking like a sieve when they did a pressure test; I had it replaced not quite 3 years ago); and one of the two valve cover gaskets (the other will likely be done in two oil changes, unless things look dire). The car is running cooler, though things aren't perfect — when I'm stopped at a light, or even running down the highway at 70 (65 or 55 isn't quite so bad), even without AC, the temperature gauge keeps creeping up, though it never reaches the danger zone mark.

My mechanic is going to replace the aftermarket radiator fans with OEM fans — thankfully his parts guy was happy to do the exchange without charging more — and we will see if they were insufficient for the task. If the overheating continues, this leaves us with a couple options, neither of which are pretty:

  1. The radiator needs to be replaced.
  2. The head gasket is going/going/gone.

When we do the fan swap he's going to test for exhaust in the radiator fluid, and we'll go from there. Any other suggestions as to what else it could be? The car generates good heat (outside of the engine itself tending toward overheating), so the heater core is fine, and we've narrowed it down pretty well so far, it seems, especially as we replaced the water pump last year.

If it turns out to be the radiator, are there any cheaper varieties you've used with success?

Thank you!

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I had this same issue. I had replaced my fans with Torqflow slim fans. New thermostat. New water pump. New reservoir. New hoses. New coolant temp sensor. New fan relays. Still did the same thing. Replaced my radiator and it fixed my problem.

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