Is The Thermostat To Blame?

[ConfederateTyrant]

Recently my temp gauge has been appearing rather low, yet still in the normal reading. My heater works perfectly fine, the top radiator hose is nice and hot, but the temp gauge is barely in the normal.

Now, there are a few different colored lines that I drew in there and I'll explain them.

Red and Pink lines: This is where the temperature needle would go before I replaced my Thermostat with a Duralast equivalent replacement. It would go to the Red area, then drop down to the pink and stabilize in between the two lines.

Orange line: This is where the needle would go to, and stabilize, after replacing my thermostat with the Duralast thermostat (I also added 1/2 quart of RMI-25 at the time of replacement). It stayed that way until recently.

Yellow line: That is the location of needle from last week when Georgia got a lot of snow and ice. It stayed in that position the entire time on two 17-19 mile highway trips.

Actual gauge needle: That was taken this morning, and as you can see, it's barely in the normal lines. The needle also stabilized there on two 17-19 mile highway trips.

Gas mileage does not appear to have changed, and I am wondering if this is only happening because of the temperatures. However, I've driven the car in colder temperatures and it stabilized at the Orange mark.

So my questions are:

1. Leave the thermostat in and see if it changes in spring/summer?

2. Replace it and see if it changes?

3. Is this more of a sending unit, or coolant temp sensor, issue?

Thanks in advance for the responses.

 

[The_Jeff]

You didn't say what vehicle.

But, if the top radiator hose is hot, I assume coolant is circulating to the radiator, perhaps sooner than expected. All the hot hose says is your thermostat is opening; we are trying to figure if it's doing so too soon.

Factory gauges are, as you know, rather numb. I just got this scan tool on ebay that shows live data, only $50 shipped, and my as-read coolant temp is within two degrees of thermostat rated temp.

With my GM stuff I've noticed thermostats failing towards cool, a good thing compared to overheating. Am a fan of Stant superstats. Seems like these things in general are so vital yet so cheaply made.

 

[ARB1977]

If is is failing its better to fail open then closed. My inlaws 95 Exploder takes for ever to warm up...i think the tsat had failed in the open position. May look into a new tsat.

 

[JHZR2]

there is seemingly really poor QC on many thermostats.

In the MB diesel community, people had issues with various thermostats not opening at the correct temperatures that they were set at.

The result was the suggestion that the box not be trusted and the thermostats be heated on the stove.

A lot of folks all over do this sort of test to verify that they don't have a dud.

I dont trust quality of most AZ parts... brakes seem to be decent, but anything else???? not sure.

It is colder, but if long-term experience says otherwise, Id suggest pulling the stat, heating it and verifying that it opens properly. If it does, then Id attribute it to cleaning and lower ambient temps. Otherwise, get a new stat.

JMH

 

[swalve]

Originally Posted By: JHZR2
I dont trust quality of most AZ parts... brakes seem to be decent, but anything else???? not sure.


I've had the same experience from all aftermarket parts places. Actually, Autozone has been better than average, but not by much. I too like their brakes.

Sad to say, it seems like the parts from the dealer are far and away better parts than from the aftermarket shops. Especially Stant thermostats.

Even with lifetime warranties, what do they care if an alternator breaks in a year? They just give you another one and send the broken one back to the rebuilder. You're the one stuck changing the part out and dealing with the hassle. I don't have a heck of a lot of car experience, but I'll bet I've never had an aftermarket part last near as long as the factory one.

 

[TexasHonda]

Try a new OEM thermostat. I think you'll see temp gauge return to normal.

good luck

 

[dwendt44]

I've heard of a guy who went through four thermostats before finding one that was good.
Tested them all in the pot of hot water and thermometer test.
Two of those were OEM, two from auto parts store(didn't mention brand). The one that was good was one of the aftermarket ones.
My 2¢

 

[mechtech2]

Thermostats are rated at their opening temp. The rate at which they open after that varies, and the flow through them varies. Also, the opening temp is not NASA accurate.
So if a new thermostat makes the gauge read differently, it is not the sending unit, unless it is a colossal coincidence.
For a street car, warmer is better for engine life and gas mileage, so you may want to consider a different thermostat.

 

[Quest]

Never had such problems with Japanese OEM thermostats bought from the dealerships. Yeah, it costs a bit more mullah but I only need to replace them once every 10 yrs or so, instead of paying/repaying again and again and praying while flying down the highway with aftermarket thermostats...

No, if your thermostat cannot get up to where it should be (assuming you bought the factory spec'ed temp thermostat to begin with, not something stoopid cold or stoopid coldest range) in the midst of winter then yest, it's definitely a faulty thermostat.

BTW: lately, we are having windchills here in beaverland down to -10C or lower overnite (tonite it's gonna be -6C), and all our cars with factory thermostats are running just like it should, no need to cover radiator with pizza flaps, etc.

Q

 

[Spector]

I have a Camry with the same issue, been that way for over a year now. Had the sending unit tested, fine, thermostat changed twice not it, guess it is the gauge itself but that is a major ordeal to replace. Also heard the rumor that aftermarket, not OEM thermostats, do not read correctly in Toyotas, engine runs fine, heater fine, etc just a guage that barely moves.

Just not worth the cost or hassle to keep playing with it.

 

[ConfederateTyrant]

Well, yesterday afternoon, the temps raised about 30 degrees outside, and the gauge moved up just a little bit more.

By the way, this is my fault for not posting, this is a 1995 Grand Marquis, and I replaced the thermostat nearly a year ago. This kind of activity didn't start until recently. I replaced it only because the original one had been installed for 12 years.

I'll get an OEM one and replace it to see how things work.

Thanks again, and anymore advice will be appreciated.

 

[Eddie]

OEM stats are usually very good. Dealers and their mechanics hate to do repeat jobs on their time.

 

[Triple_Se7en]

What is your most recent ratio of coolant-water mix?

My first impression was the thermostat. If you change it, get the OEM (Motorcraft?) part. That may require purchasing it from the dealer.... I dunno!

 

[ConfederateTyrant]

Coolant ratio hasn't changed, it has always been between 50-60% coolant.

 

[Tosh]

Originally Posted By: ConfederateTyrant
This kind of activity didn't start until recently. I replaced it only because the original one had been installed for 12 years.

I'll get an OEM one and replace it to see how things work.

Thanks again, and anymore advice will be appreciated.

Get a new OEM radiator cap while you're there (if it's also been in for 12 years).

Frankly, I think you should wait until summer temperatures and decide then.

 

[ConfederateTyrant]

Already have a OEM radiator cap, and it'll probably be around Spring by the time I replace the thermostat.

 

[ConfederateTyrant]

I forgot to add, the OEM cap was replaced with a new one two years ago.

 

[55Test]

I had a 93 Crown Vic about 2 years ago, and it always ran with the temp gauge at about where the yellow mark is on that picture. It consistently got 26 or more mpg on the highway at 62 mph, and about 15-16 in town. The engine had an EGR problem and didn't like lightweight oil (valve seals) but otherwise ran great. Does your 95 have the cast or aluminum intake manifold?

 

[Donald]

By the way if you decide to check the thermostat in a pan of water, you need to hang it in the water off string tied to each side of the pan and use a candy thermometer held near it to tell the temp. Nothing should be touching the bottom or side.

 

[ConfederateTyrant]

I fixed the EGR problem on mine, since it was just a flow issue related to the intake ports. I'm not sure which manifold it is, it's not the one that was introduced in 96 that had all the leaking issues.