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Discussion Starter · #1 ·
Hi all,

2004 4cyl, 150k.

I noticed my temp gauge is fluctuating the level of "one bar" on the temp gauge. After sitting at a red light or in traffic it will drop down a bar, and then after accelerating and cruising at ~50mph it will go up a bar. It's not getting to the point of overheating yet, but I hope to take care of this before it gets there. Thoughts? thermostat?

I bought the car at 130k two years ago and she's been good to me since. Hope to keep it for many more years. In terms of cooling system related maintenance, I did a drain and fill a couple months ago with Super Longlife OEM pink fluid.

Thanks all!
 

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Clean out the radiator fins with some AC coil cleaner, I've seen extremely clogged radiators/ac condensers act like this since at idle there's less heat made by the engine and the coolant hangs out in the radiator longer, a weak radiator can cool it down well enough, but when driving there's more heat being made and the coolant is moving through too fast to drop the heat load since the fins are blocked. You may need to remove the radiator fan to do the cleaner, or just replace the radiator. Inspect by shining a bright light through the condenser and radiator, you should be able to see light shine through anywhere you shine it.
 

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Discussion Starter · #6 · (Edited)
Clean out the radiator fins with some AC coil cleaner, I've seen extremely clogged radiators/ac condensers act like this since at idle there's less heat made by the engine and the coolant hangs out in the radiator longer, a weak radiator can cool it down well enough, but when driving there's more heat being made and the coolant is moving through too fast to drop the heat load since the fins are blocked. You may need to remove the radiator fan to do the cleaner, or just replace the radiator. Inspect by shining a bright light through the condenser and radiator, you should be able to see light shine through anywhere you shine it.
Thanks for the suggestion. I took at a look at the radiator when I did the drain and fill and it's clean on the inside. Nice shiny fins.
 

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That's encouraging kind of, still try shining light through. Not uncommon for stuff to get stuck between the condenser and radiator like a wall of fibrous gunk and dirt. If the fins are clear it could be scaled up inside the radiator, only way to know that is to look inside but if you can't see down the end tank at the actual ends of the tubes you can't really tell. With 130K might not be unwise to just change it out, if you live in an area with temp extremes the plastic end tanks get weakened with age as do the radiator necks.
 

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Could it be the radiator is getting clogged or a thermostat problem slowing the flow down when at driving speed?
 

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'05 Solara 'Vert & '07 ES350
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I agree that it might have trash between condenser and radiator, not sure with this particular car, but it's often easy to pop pins at top, holding radiator in place, and then tilt it a bit to see if anything going on.
Hose it off no matter what.

Aside from that, and given nothing wrong with radiator itself, and since it shouldn't be the fan(s)
--since it gets *cooler* at stop light--
that leaves the thermostat, or, a failing water pump.

Symptoms are not really consistent with either one of those, but, to check water pump, look closely for powdery, pinkish, antifreeze stains near the pump.

Whoops, forgot that serpentine belt is not likely candidate, but still a possibility.

No way I know to diagnose thermostat without pulling it out. If you do, and replace it, test the new one -boil it in water on the stove- to see that it opens & closes nicely. I've put in brand new ones that were defective.

Last, but not least, could be a head gasket, but only if the car's been overheated at some point.
Sniff test, smell any anti-freeze??,
....or mechanic's have a tester for combustion products in the coolant.

No loss --even minor loss-- of coolant???
 

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Discussion Starter · #11 ·
No loss of coolant at all and no coolant stains near the waterpump area. I will change the thermostat at the next oil change. any suggestions on where to purchase the OEM one (other than directly at my dealership)? I see amazon has it for $20 without a gasket.

I was also planning on changing the serpentine belt because I see that it is starting to develop some minor cracks. But I don't see how that can affect anything because it doesn't slip?
 

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'05 Solara 'Vert & '07 ES350
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OEM - Amazon's always good. A brand name, like Gates, for example, from NAPA or other parts store is easily as good.
There's no magic from the cardboard box that says Toyota on outside, but probably contains a rebranded part.
Needed a new coil for spark plug last year. Toyota: $85 Denso: $45 Who makes that coil for Toyota? Denso.
 

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'05 Solara 'Vert & '07 ES350
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I agree, but I've yet to run across an aftermarket thermostat that's the same beefy build quality as OEM Toyota or OEM Honda that didn't cost as much or more than the dealer parts from Toyota or Honda, and to boot came with an inferior gasket.
Interesting. My only personal experience with thermostats, in 50+ years of driving, has been with BMWs.
Never had a failure on any other car. BMW straight-sixes are notorious for blowing head gaskets if overheated; Ask me how I know.
To this day I wonder why someone hasn't invented a thermostat that can *only* fail OPEN. :(
 

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Thank you !!
 

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Might be the thermostat, I suggest Stant 48128 Xactstat + O'ring for water inlet pipe, thermostat come with an gasket and the design and quality is similar to oem. If your car is a 4cyl, then it should be an easy job 2 bolts to remove, but I recently did on a 05 Camry 1mzfe v6 and it wasn't a easy job. It took me almost 8 hour from night till early morning with break due to back pain, a lots of sweating and drinking water and a good friend helper holding the lamp and mirror. It took me hour to find the last hidden bolt from the thermostat housing with the cramped space and re-assembling wasn't easy. I could say Stant is a good quality thermostat without paying dealer price and that parts is made from japan. I just let the car run for 45mins with max heat and full fan speed to purge air with new coolant while taking a shower and changing new clothes. Friend was very helpful but angry that 1 stupid parts took all night long and it will be my last thermostat by DIY. We didn't lost track of any bolt or forgot how to re-assemble, because we took picture for reference but didn't expect that need 8h the whole night for complete a thermostat job.
 

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