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Discussion Starter #1 (Edited)
Overheating when going uphill - "SOLVED!"

My '96 Taco overheats when I go uphill or make her work a little in snow and such. I thought it was the viscous fluid coupling (Fan clutch), ordered a new one, but it made no difference. The rad is not plugged with mud/ snow, etc. Both rad hoses warm up. I changed the antifreeze. She is fine when idling or driving in town or on the highway. This only happens when she has to work a bit.

According to my FSM, the thermostat has 2 phases, and I am beginning to think the second phase, i.e. full-throttle opening, doesn't happen. I suppose this would be the next thing to check (on the stove), unless anyone has a better suggestion. Any ideas? Thanks?
 

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If the truck is overheating when struggling through the snow, something is definitely wrong - cuz snow tells me it's cold out! One of the hoses is the return hose, and the other is the out hose. When you say both are warm, do you mean that they both feel just as warm as the other? The return hose should be hotter than the other hose. Even so, that doesn't necessarily mean that the radiator or any of the coolant passages is not clogged or partially clogged.

I would flush the whole system and fill it back up with a 50/50 mix of Toyota coolant (it's expensive at $17!) and distilled water. Be sure to "burp" the system when you fill it back up by letting the truck idle to normal operating temp - just keep adding the 50/50 mix as the system burps the air bubbles out of it. I would also replace the radiator cap and thermostat with new ones - a 96 means that the original parts are almost 9 years old.

Also, have you noticed any coolant loss? If so, check the radiator for any pin holes, the hoses and hose clamps, the coolant overflow reservoir for any holes and leaks, the water pump for any leaks around it, and check the oil dipstick tube for any milky/oily mix. If the dipstick tube looks milky, then the headgasket likely blew, causing coolant to leak internally.

Hope this helps.
 

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Discussion Starter #3
Okay, so I installed a new OEM thermostat - still overheats. Bought a new radiator cap - still overheats. It seems to have something to do with altitude, but maybe it's just a coincidence. I've taken her up this hill in 4 high, and everytime I get to the 7 mile marker, she starts overheating.

The lower hose is cooler than the upper. I am not loosing any coolant, either. With aHG problem, there would be other symptoms like milky oil, etc., right? I have one noisy valve, and I've been threatening to adjust the valves, but this shouldn't cause this, right? I checked the ignition timing the other day, and it was dead on. I did notice that the strobe light sometimes missed a flash, not sure what to make of this.

Any ways, so far, I've drained and repleced the antifreeze, new rad. cap, new thermostat, tried a new fan clutch - and nothing helps.

So how do you know the rad is clogged inside? I had her idle for some time today to burp the system, and had a trouble light shining in through the radiator cap hole, and she flows very well, once that thermostat opens up. Also, the coolant seems to drain, and fill normally.

I see in my FSM they talk about this Engine Coolant Temperature (ECT) sensor, that sends signals to the ECU. Could it be this?

What about the waterpump? I suppose the coolant wouldn't flow as well as it is, or maybe it isn't. It sounds as if removing it is somewhat of a chore. The guys over at the stealership already refused to refund me the $150 for the fan clutch I only had on the truck for an hour to see if it is the problem. I'd hate to buy a new pump, install it, find out it's not the culprit, and again not be able to get my money back, cause it's been used.

If I had any anti-depressants handy, I think I would have had some.
 

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Hmm. Sounds like you did all the obvious - flush, fill and burp the system and replace the t-stat and rad. cap. And yes, if the dipstick looks milky, that's usually a sign that the hg blew. But you report no coolant loss, right? As for the valves, I have no idea if that would cause it to overheat.

Unless someone else can chime in with any other suggestions, I think your best hope is to take it to radiator shop and have a pro diagnose the system - pressure test it for leaks and check for any partial blockage (if not a clogged radiator, maybe the heater core or one of the passages? - even if it looks like its flowing, it could still be blocked a little bit - just enough to cause it to overheat?).

Anyway, here's a bump for you and good luck.
 

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Discussion Starter #5
equin said:
Hmm. Sounds like you did all the obvious - flush, fill and burp the system and replace the t-stat and rad. cap. And yes, if the dipstick looks milky, that's usually a sign that the hg blew. But you report no coolant loss, right? As for the valves, I have no idea if that would cause it to overheat.

Unless someone else can chime in with any other suggestions, I think your best hope is to take it to radiator shop and have a pro diagnose the system - pressure test it for leaks and check for any partial blockage (if not a clogged radiator, maybe the heater core or one of the passages? - even if it looks like its flowing, it could still be blocked a little bit - just enough to cause it to overheat?).

Anyway, here's a bump for you and good luck.
Thanks. Sounds to me like it is either the waterpump or the HG. I am busy packing, because we're moving the end of this month, so I won't be able to look into it for awhile. As soon as I find the problem, I'll let you know. Thanks for the info everyone.
 

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If the radiator is clogged you can tell by running your hand over it. If it is clogged the surface will have different temps on it. Have you ever used a stop leak product? That was a big culprit in mine. How old are your hoses? If they are original I would look into replacing them. They can actually suck shut under pressure.
 

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Discussion Starter #7
Toyasaurus said:
They can actually suck shut under pressure.
Funny you mention this, because the other day I noticed the upper hose sucked closed after it sat for about an hour after I drove it up this hill to test it.
 

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Sometimes after a flush and re-fill, air will get trapped. Usually happens on rigs with body lifts (not to say it couldn't happen on a truck with out), the air gets held in the heater core. the hose suck shut after it cools says it's low on coolent. Try burping the system again, with the front end raised as high as you can get it.. (ie steep drive way, or tall floor jack) this worked on my 85 4Runner with a 2" body lift.. If there is no air, Head Gasket.. a small leak letting the compression into the water jackets.. then the air pushes past the sensor, the gauge goes up, and the air excapes though the over flow.. Good luck!!
 

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On my 86 turbo same problem it was a head gasket, if you burp the system and still air is in their then their is a good chance of a head gasket. Sure fire way to tell is white smoke that really burns if you happen to get a wif. I mean don't go sucking the exhaust pipe, and I know if its cold out its hard to tell, but when you smell a head gasket you'll know. Some water pumps have a wheep hole, a tiny hole that will leak a drop or so if its bad, are your belts slipping or broken? Might be somthing simple, keep us posted.
 

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Hg problems aren't always obvious. My HG on the 2.7L '97 that I have is blown - only symptoms are a miss on cylinder #3 at cold idle, missing coolant and the familiar and sad smell of cooland from the exhaust. :( Needless to say, I'm not about to drop $1500 on a HG (or worse, a head) for a 130k truck. *sigh*
 

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Discussion Starter #11
Thank you everyone for all the good advise. As many of you have suggested, it was in fact a clogged inner radiator after all. I put in a new rad, ran her up that same hill, and everything is good. Thanks again.
 
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