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Old 08-08-2004, 12:08 PM   #1
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Default Thermostat Question

I just bought a 99 bonnie and have a question about the thermostat. I read that they put a 180 degree thermo in all the 99 bonnies. Is this true or is it just on SOME of the 99'*. If not, how can i make sure i have the 180 degree thermo? Also, does the thermometer have a temperature regulatory function, ie does the thermostat reading cause extra fans to turn on etc?

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Old 08-08-2004, 01:15 PM   #2
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The stock 99 PCM will turn the fans on at 210F and the stock thermostat is rated at 195F. If you think the previous owner changed it out, just take the 2 bolts off the main radiator hose arm and pull the Tstat out. The temperature is engraved on the back, but do this all when the engine is cold.

Any Bonneville can benefit from a 180 stat to allow coolent into the engine at a lower temp. Helps preserve the life of your engine a little longer.
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Old 08-08-2004, 01:17 PM   #3
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We heard that rumor, too, but haven't seen any proof of it. Every 99 I've seen has the 195. The ECT sensor (engine coolant temp) in your lower intake manifold is what the PCM uses for turning the fans on, but not until 220. A 180 won't help you in stop/go city driving, only if you're moving air through the rad. A drilled 180 can help a bit, as it allows more flow, but the ultimate is to do the drilled 180 and a fan bypass switch.

The ULTIMATE ultimate is to automate the fan override to come on at 200 using a thermistor or adjustable thermostat.
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Old 08-08-2004, 01:28 PM   #4
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thanks for the tips. is there a guide on how to change out the thermostat with a drilled 180 or any of the other things you mentioned? also, i have a one month warranty on the car. how can i tell if the upper / lower intake is damaged already?

i appreciate it!
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Old 08-08-2004, 01:52 PM   #5
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Quote:
Originally Posted by Strangelove
thanks for the tips. is there a guide on how to change out the thermostat with a drilled 180 or any of the other things you mentioned? also, i have a one month warranty on the car. how can i tell if the upper / lower intake is damaged already?

i appreciate it!
There'* been some controversy on the 99 intakes. I'm not sure I've seen one fail yet, but it may have to do with the production date. There'* a few topics regarding that here. Can you take a picture of the casting date on your intake? It'll have arrows pointing to numbers.

For the thermostat, just get the 180 of your choice (it must be the same series as the 195, any auto parts store can help you with the fit) , the fiber housing gasket, and the rubber seal for the rim of the stat. Drill two 1/16" holes in the flat part where they won't interfere with the rubber seal, de-burr the holes top and bottom with a larger drill bit by hand, and rinse well.

The swap procedure is simply removing the 2 nuts on the housing, lift it up, and carefullyy clean the surface. Stuff a rag in the lower intake, or leave the old thermostat in while you do this so that the debris from the old filter doesn't get into the system.

It'* really straightforward, but I suggest spending 12 buck on a Chiltons #28200 manual. It'll walk you right through it. Torque specs are in techinfo, specifications at the top of the page.
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Old 08-08-2004, 03:07 PM   #6
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Something else I'd like to add. Not sure if you are willing to modify your engine, but I personally love the combination of the 180 stat and INTENSE PCM. The stat opens at 180 and the fans come on at 180...car never sees 200F.
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Old 08-08-2004, 04:46 PM   #7
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The cheaper answer is to get one of the several automatic switches offered by Summitracing.com. Source it to power, plug the sensor in the rad, hood the fans to it, and adjust it to whatever you want.

http://store.summitracing.com/partde...N=120%20304235
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Old 08-08-2004, 05:42 PM   #8
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that sounds MUCH easier! any drawbacks to doing this as opposed to replacing the internal thermostat?
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Old 08-08-2004, 05:53 PM   #9
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I would STILL do the thermostat. It helps prevent the initial heat soak of the engine.
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Old 08-08-2004, 06:05 PM   #10
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No no, this MUST be done WITH a cooler thermostat. The fans aren't capable of keeping the engine at 180 with the t-stat set to open at 195. They'll burn out trying
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