anyone else experience FAULTY New Thermostats?

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Just replaced the 190* t-stat in my 93 JGC with 229,000 miles. Old one opened at the right temp, but not all the way. So, while repairing a gasket leak, I opted to buy the stant part w/ 1 yr warranty (the least-cost stat, as opposed to lifetime warranty).

Once replaced, engine temp quickly rises to ~195, then slams down to 170. Then up to 195, slams down to 170. All day long.

Now, the h20 pump was leaking, so I just had it replaced. The new pump has slightly changed things... Does this now:

- warm afternoon: engine temp quickly rises to ~195, then slams down to 170. 195, 170, up to 200, stays put.

- chilly morning: engine temp quickly rises to ~195, then slams down to 170. 200, 170, up to 210... and keeps bouncing.

It cycles 2-3 times/minute.

Clues?
1. I suspect that there was air left in the system after pump replacement as the reservoir has dropped some.
2. No bubbles in the reservoir during hot idle, hot revving.
3. no oil or oil spoo in the coolant
4. no coolant in the oil
5. twice I've found where coolant has burped out of the reservoir cap. not sure why, it's only 1/2 full.

Anyone else seen this?

Mike
 
1. yes, possibly
2.doesn't matter. Refer to 1.
3. it just means that your oil and coolant are happily staying separated.
4.again, Refer to 3.
5. purge your cooling system to rid of any trapped air pockets.

2 things I can think of (a) have you perform any chemical flush to your cooling system? (2)did you install your thermostat in the proper orientation? (barrel side towards the block, pointy side towards the rad)?
 
With Stant, all the time. They'll either fail new, or within a couple of months later. I've never had a stant last more then a year. And, after having dozens cause issues, Stant 'Economy' is one brand I avoid.

For thermostats, stick with OEM if possible.

Make sure you understand how to burp the JGC.
 
Quest: thanks for the thoughts. I mention 2 3 and 4 because they would suggest a head leak, which would also cause "1" continuously. by now, 5 should be covered.

No chemical flush. In my experience they remove too much, or too little. :-(

Orientation. absolutely. it only fits one way anyway, but yes that would definently cause..

unD.: AHA! yep. I went with stant "economy." a friend just installed the upper level stant only to find it's 30* off. Advanced Auto only stocks Stant. I've heard that Murray also blows chow. Suggested brands? We have NAPA, Advanced Auto, Orielly's (murray) and Autozone here.

mikey!
 
I only get the thermostats from NAPA or the dealer, and I always buy the best one they have; I don't trust any of the others.

I don't use the air bleeder screw on mine; I just back the radiator cap off one click and bleed it out that way. When you see big gulps of air coming out the reservoir, you'll know it bleeding good.

When the water starts to boil inside the reservoir, it's time to tighten your radiator cap to its final click.
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Online, NAPA's primary brand is Stant, and the stant "superstat" name. also a "racing only" brand - - um, mr gasket, maybe?

mike
 
If NAPA's best most expensive thermostat is a Stant Superstat, then fine; get that and save your receipt. Get the factory temp too!
 
Yep, finding brand name parts is tough.
Visit the dealer and overpay for OE parts.
MrGasket, Prestone,....might be worth trying to locate. Even if not in stock, most of your autopart stores can order by brand/PN.
The robertshaw and cooperstandard thermostats are tough to find at ANY autoparts stores. Try the flowcooler.com website. 330 or 333 should be the size. I would probably use a 180 or 195 depending on driving style---investigate PNs 330-180, 330-195, 333-180, 333-192

BTW, once you know the size of your thermostat, you can research other 'makes & models' that use it. This means you could also get OE parts from the local Ford, Toyota, GM or..... if you know the year/make/model/.... So, you have other choices at various domestic speed/4x4 shops.

Superstant/Delco/Gates/Napa clones are definitely a better 'risk' then the economy choices. By all means, get the superstant over the economy any day.
 
Just Go to AA and asked them to bring out the cheap thermostat and the expensive one, you will see quite a difference in the mechanism, the cheap stat would spike because it hung up, this was on my 4L Jeep Cherokee.
 
First, my comments assume that your posted temperature readings are from the dashboard instrumentation.

I think before you make any more changes, it would be valuable to hook your vehicle to an ODBI engine scanner. On some vehicles, the dashboard temperature indication is separate from the temperature sensor going to the vehicle's control module. I have first hand knowledge of this possibility having needlessly performed a thermostat-ectomy. Also, some temperature sensors are single wire affairs that rely on a ground to the engine to complete the circuit. A fluctuating ground may cause some bizarre readings.

However, you might actually have entrained air or a poorly performing thermostat or a combination of both. If you are able to confirm it is the thermostat, I’ll second the suggestion to go back to an OEM if it’s available or if not a Stant Superstat from NAPA.
 
Aftermarket Thermostats = Junk

Thermostat is one of the most important components in modern computer calibrated vehicles! OEM is generally better because it usually has a heavier spring and a better build.
 
I ran a stant for a few years in '96 Subaru without any problems, but when you compare it with the OEM thermostat you can see a big difference:
thermostat1.jpg
 
Thanks for the comments. Went to AA yesterday and talked with them about it. They have frequent returns on the cheaper stats because the motor mechanism is weak and gets hung easily. Compared to the superstat, it wasn't as robust. Wish the clerk who sold it to me could have mentioned that. They basically "good-faithed" an upgrade to a superstat on warranty. I'll drill the tiny bleeder hole and install it sometime soon.

I've only replaced a handful of these on my cars and friends' cars but have never had this happen. But, this is the first time I've gone with an "economy" level stat. Won't do that again.

Mudcat - nice "out-of-the-box" ideas. Yea, I've had to chase ground problems before. I didn't really think of that b/c the symptoms lined up with installing the new stat. However, you're right...15 yr old oem gauges are, well, 15 yrs old. Oddly enuf, the only one that sticks is the speedo, and its very mild...

Thanks y'all. It's nice to have some other opinions/experience points/angles to approach from.

Mike!
 
I'm using a Duralast thermostat in my Integra right now and it works great. Haven't had any issues at all with it, and it's been in the car for over 7 months now. Plus, it wasn't very expensive
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OEM or "High Accuracy/Performance" thermostats only. I've found standard and/or economy grades cycle so violently it isn't even funny.
 
I've installed quite a few cheap aftermarket thermostats. I've had a couple that just didn't work or only worked for a short time... and I've had several others that opened too early or exhibited wierd cycling behavior. I finally learned to just pony up whatever the local dealer wants to charge me. The cheap ones aren't worth the hassle.
 
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