Temp Gauge Fluctuating-Thermostat or No

[goatfarmer]

!990 T4r, V6, Auto, with 210K.

Had a few chores to take care of this a.m. but after traveling approx. 50 miles noticed the temperature gauge started moving from the normal range to extreme hot, then within a few seconds drop back down to the normal range, decided to return home and this normal to high fluctuation continues for the return.

Upon return, radiator took approx. 1 quart of water. Replaced the belts approx. 1 yr. ago, belt tension appears okay?

Seems the oil pressure is extremely low @ idle, but runs below, to normal when traveling?

After letting it set an hour I took it for a 10 mile test drive and the temp. remained in the normal range. I would not feel comfortable taking extended trips; although, not that knowledgeable it would seem the problem is possibly related to the thermostat; is so, then I thought replacing may put my mind at ease?? I have some basic mechanical skills and appears the thermostat can be removed from the bottom by removing the lower radiator hose and the 2 bolts from the thermostat housing??

Checked local NAPA store and they list replacements from $40 to $10, which includes the seal??

Comments, suggestions appreciated!!

 

[flyinhawaiian01]

Could be the thermostat sticking, or it could be a huge bubble of air caught in the system. Rather than pulling the thermo out first, try bleeding the system, its the easiest fix right now. If while you're driving, you turn the heater on to full heat and hear a gurgling sound, you definitely have an air pocket.

Make sure to get that front end up as high as possible to burp the system! I put my truck up on ramps while parking on an inclined driveway, and use a step ladder to get to the radiator! With engine cold, turn heater on full heat, open radiator cap, start engine and bring up to full operating temp. This may take as long as 10 minutes +, so be prepared to wait a while.

When you see the water in the radiator neck start to move fast, it should be up to temp and the thermostat has finally popped open. Refill with antifreeze to keep it topped up while its running. Yep, it can get messy if you spill it and it gets into the fan.

Put the cap back on, check it daily for a week or two, making sure its not losing fluid.

If it continues to creep up in temp and you don't lose any water, its definitely the thermostat. I believe the v6 is a pain to get to the thermo, but its necessary if you don't want to pop head gaskets, or worse, blow the engine up by overheating it bad!

 

[goatfarmer]

Greatly appreciated, will give burping the system a try tomorrow. I thank you!!

 

[ellis36]

For what it’s worth. I had an ’89 LC that did the exact same thing. Turned out to be a bad connection on the circuit board for the instrument cluster. Probably a ground connection. When it was happening I could put gentle pressure on the speedometer face or reach up under the dash and flex the wiring and make it go away.

ellis

 

[ThorInc]

A stock OEM thermostat will fall into that price range you referenced.

 

[goatfarmer]

I do appreciate U'Alls input.

Fairly certain it's a mechanical issue; whether there's an air pocket, or faulty thermostat the engine gets very hot when it starts its thing.

Heading to the local auto parts store and pick up container of anti-freeze then try burping the system, as mentioned, best try the least expensive, and labor intensive approach before disassembling components.

Checked Sponsor's websites and seems they carry all brands of thermostat, did not find a 'Toyota Supplier', but will research further if replacing becomes necessary?

Found I can purchase ' By Toyota' replacement thermostat on my Amazon Prime free shipping membership, figure if they are going to punk me for the cost of subscribing might as well use it, placed the item in the cart and just a matter of clicking and should receive within couple days.

Again, greatly appreciate the input!!