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94 Honda Accord--overheating!

Alright, car's overheating, but generally not at under ~55mph or so. When I hit the highway and accelerate, the thermostat climbs and hovers 3/4s of the way to red. But only sometimes. Sometimes, often when I'm going down a hill, it will swings down to normal. Once it's gotten hot, if I take it off the highway and am idling or driving in the 15-40mph range, the temp gauge will spike. But only sometimes. Sometimes I'll hear the fans kick in while it's idling/overheating. The temperature will go back to normal, and then rise again and stay there or spike (seemingly randomly). It's never reached all the way to the red, but it toes the line. And I take the darn thing into the shop and it refuses to overheat and my mechanic looks at me like I was dropped on my head as an infant. Ahh!

I've taken the radiator reservoir out and there seems to be green fluid (antifreeze/coolant?) in the water (have flushed it repeatedly)...and over the course of several weeks, the water level itself will go down. Both fans and the thermostat have been replaced in the last 6 months. Additionally, the timing belt and serpentine belt have been replaced within 5 months, as have affected pistons.
((S/N--RPMs are really....low? ~2500 @ 75mph? but don't seem to correlate w/temperature. would they effect it?)

I took it into my shop and they said "we ran all the tests and couldn't find anything wrong." Cool? I'm at a loss. This is not my forte, and I'm too broke to throw money at it until something works. Any ideas?
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Comments

  • edited November 2012
    The cooling effect when it goes downhill kinda points to an air bubble in the system. It may need to be burped:
    Park the car on ramps, slightly uphill or with the front wheels on the curb.
    If cold, open the radiator cap.
    Start the car and goose the accelerator pedal a bit. Nothing crazy but make it go to about 1500 rpm.
    Watch for air bubbles to burp out of the radiator neck.
    Every time you see a bubble, add coolant.
    Eventually you won't see bubbles anymore.

    Btw, only fill with HONDA coolant. Using off the shelf "pepboys' coolant is referred to as "Hondacide" - it will kill that engine. Hondas are quite picky when it comes to coolant and other coolant can actually do damage. There are other brands out there that are compatible but better safe than sorry.
  • I always hate to say this, but try a better shop. There are numerous possible causes, and any competant shop should be able to diagnose this one. Keeping an automobile engine at the proper temperature does not involve rocket science, but it does involve an understanding of how the system works. Your shop seem sto lack that.

    Sorry, that's the best I can offer. I'd suggest a bunch of tests, but my impression is that automotive technology is not your field of expertise. That green fluid is a good thing. I truely think your best and heapest option is a qualified shop......or a good buddy who is a knowledgable car guy.
  • If the needle on the coolant temp gauge doesn't go into the red zone the engine isn't overheating. It's still operating in the normal range.

    Tester
  • First thing I would do is replace the radiator cap, it is cheap and the symptoms you are having are common for a radiator cap that is not holding system pressure.

    BTW, Honda did not have a special antifreeze back in 94, but a universal long life coolant would be the best choice for this car. Stick with a major brand like Prestone, Zerex or Peak. As for bleeding, there is a bleed valve on the gooseneck for the thermostat.

    Follow the LOWER radiator hose to the back of the engine. The bleeder is about 3" from the end of the hose and looks like a bolt with a pipe sticking out the head. Loosen it about a turn or so until coolant starts coming out the hole, then tighten.
  • edited November 2012
    The operation the OP is describing is not normal. It's definitely better to get it corrected now than after the engine has overheated.

    There are a whole lot of possible causes, including but not limited to a radiator internally crudded up, a collapsed hose inner liner, and a water pump with eroded impellars. I was tempted to suggest some tests, such as testing the new thermostat, checking the pump flow and mapping the radiator with an infrared pyrometer, but my sense is that the OP isn't car-saavy enough to perform these tests.
  • Thank you all for your help! the_same_mountainbike is right, I don't have the know-how or tools perform many tests, but I can at least give burping the system a shot. Thanks!
  • Burping the air out is a good idea to try. You need to find out what is causing the coolant to disappear though. Your symptoms to me remind me of when my car's radiator sprang a small leak. Then the radiator couldn't hold pressure and the cooling system -- even if it hadn't lost much coolant -- had a difficult time keeping the coolant temp in check. Ask your mechanic or a radiator shop to do a pressure test on the cooling system.

    Be sure you end up with coolant in the system with enough antifreeze that won't freeze up on you of course.

    One more thing, if you see white smoke coming out the exhaust, that's an indication the coolant is making it's way to the cylinders. That can cause similar overheating symptoms. To fix it would most likely require a new head gasket, which is a budget buster but may be required. Mechanics know how to test for this.
  • I would start cheap and easy initially. First, burp the air out of the system. Free. If that doesn't fix it, change the radiator cap, use proper pressure from factory. $10. If that doesn't work, change the t-stat. $20. So far you've only spent a little time and money, probably less than $30 and an hours time. Next I would take a serious look at the radiator, they wear-out and are not too expensive (got one for my '89 for $100) and are pretty easy to change. After that, let us know. Accords are pretty simple and these issues are not too hard to trace to a proper fix. I can direct you to a website that is FULL of older Accord owners, mostly a fix-it type forum like this one but specific to older Honda Accords. Keep driving it . . . my '89 has 565,000 miles on it! Runs great, no kidding. Rocketman
  • edited November 2012
    I think that needle dropping when he's going down hill is a clue: the thermal sensor is along the top of the block and that sensor does not behave when it isn't fully emerged in coolant, as it would be with an air bubble in the system. When you roll down hill, that bubble shifts and the sensor is fully emerged, causing the gauge to go down. IOW, that sensor needs to be submerged in coolant all the time.
    Like I said: the first thing to try is burping the system. On some cars, when you do refill the coolant, it is best to take the top radiator hose off, stick a funnel into it and fill the block first. Then, when it is near the top of the hose, reconnect that hose to the radiator quickly and then fill the rest of the system by means of the radiator.
    Usually that prevents air bubbles.

    Oh, and Hondas do not take just any coolant. You do have to be careful with the type you pick
    Since our OP clearly isn't very familiar with coolant but may be willing to try burping the system himself, I suggested he go to the dealer to get it, to make sure he gets the right stuff.
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