How hard to replace thermostat?

[hofffam]

I'm quite sure my 97 needs a new thermostat. Mine is one of the cars with a very slow warmup. Not an issue in the summer but fall is upon us and winter is coming where this matters more.

I searched and I found that several here have replaced their thermostat, but I couldn't find any description of the work involved.

Can anyone summarize the main steps required to replace the thermostat? How long should it take? I am reasonably skilled and have most typical tools. Besides the thermostat itself - what other parts need to be replaced (gaskets, o-rings, etc.)?

 

[Tony Montoya]

Slow warm up is normal. It can take 10 minutes of idling in winter for the temp to even begin moving. My 850 is hot before I make it out of the parking garage, the NSX takes 5-10 minutes of driving to warm up fully. Then you have to wait double that time for the engine oil to get up to temp before flogging the car.

 

[chudson1549]

I'm quite sure my 97 needs a new thermostat. Mine is one of the cars with a very slow warmup. Not an issue in the summer but fall is upon us and winter is coming where this matters more.

I searched and I found that several here have replaced their thermostat, but I couldn't find any description of the work involved.

Can anyone summarize the main steps required to replace the thermostat? How long should it take? I am reasonably skilled and have most typical tools. Besides the thermostat itself - what other parts need to be replaced (gaskets, o-rings, etc.)?

Pretty simple from what i remember.
Remove the air filter box assembly out of the way.
Drain the coolant down so that the bleeder valve in the throttle body does not purge coolant at all. Lossen two bolts from the location replace and reverse.
Refill and bleed the coolant system like the manual says

 

[Larry Bastanza]

It is not too difficult. The thermostat for 1997 comes w/gasket.

P/N 19301-PR7-305 (list is about $32)

If you download the service manual it is pretty clear how to do it.

The short version:

Drain coolant
Remove air cleaner assy
Remove throttle body rubber bellows
Remove two bolts in thermostat housing
Change thermostat
Fill coolant
Test Drive
Top off coolant

Honestly the coolant fill is the longest part if you have not done it. You can search on prime, I have described it in detail at least once.

HTH,
LarryB

 

[hofffam]

Slow warm up is normal. It can take 10 minutes of idling in winter for the temp to even begin moving. My 850 is hot before I make it out of the parking garage, the NSX takes 5-10 minutes of driving to warm up fully. Then you have to wait double that time for the engine oil to get up to temp before flogging the car.

I've been reading the threads here on warmup time for many months now. Last winter (Texas) my NSX didn't warmup for at least 7 miles, or 10-15 minutes of driving. By warmup I mean gauge comes off bottom and I feel heat. Many here have reported similar warmup times - which improved significantly with a thermostat change. So I figure I'll replace it for $30-$40.

It is interesting to me that my Ridgeline is at normal operating temperature in 2 miles.

In any case, thanks for the walkthrough of the replacement steps....

 

[Larry Bastanza]

I've been reading the threads here on warmup time for many months now. Last winter (Texas) my NSX didn't warmup for at least 7 miles, or 10-15 minutes of driving. By warmup I mean gauge comes off bottom and I feel heat.

There is littel doubt your thermostat is open. I am sure when you pull it, the rubber seal around the plunger will be mushroomed open. I have seen this many times.

Good Luck,
LarryB

 

[hofffam]

FYI: looks like the part number for the thermostat assembly changed. I made the parts guy at McDavid Acura in Austin double-check, but he says the new part number is 19301-P8E-A10. $31.60.

 

[Larry Bastanza]

FYI: looks like the part number for the thermostat assembly changed. I made the parts guy at McDavid Acura in Austin double-check, but he says the new part number is 19301-P8E-A10. $31.60.

Agreed, it must have just been updated, since the on-line sites still have the old number. You are good to go with the number above.

Regards,
LarryB

 

[ftuhy]

My '96 had the exact same slow warm-up problem. Last winter in NJ it was taking 10 miles to warm up. I pulled the old thermostat, and the rubber seal around the plunger had mushroomed just as Larry noted he has observed a few times.

I went to NAPA and got a new thermostat and gasket for $20. A much simpler design with no rubber seal. The car now warms up in about 1 mile in the summer and at the same time runs where it should with the A/C on despite all the hot weather we had in the northeast this year.

It was an easy & quick job - under an hour while taking my time.

Other than one O2 sensor, that's the only part to fail on my NSX in the last 7.5 years.

Frank
'96 NSX-T, red/tan

 

[nsxotic911]

What do people think about the aftermarket spoon or mugen that open at 10C earlier..?

 

[Daedalus]

Sounds like a waste of money. Engines are more efficient at higher operating temperatures. They're cooled down to comply with material limitations. A cooler-than-stock thermostat has no benefit.

 

[BATMANs]

Slightly offtopic, but can the thermostat be deleted and ECU re-worked to think that it's in warmed-up mode for the correct A/F ratios?

Engine heat is the enemy of performance and engine life, so why not start with the cooling system?

 

[Daedalus]

What is it you know that the engine teams from all car companies don't? It is not coincidence all aluminum engines have roughly the same tstat settings and that all iron engines do too. And it's not because they companies are just copying one another.
In answer to your question--yes. You look up the temp-resistance table or chart in your vehicle's FSM, find the resistance that correlates to the ECU's closed-loop temperature, and buy a 40-cent resistor that matches the resistance. Then you unplug the TW sensor harness and splice the resistor in. Not only will you be able to rev the piss out of it when it's at 65*, but you won't have to suffer through degraded performance if the engine ever begins to overheat...at least until it fails.

 

[hofffam]

I finally replaced the thermostat yesterday. I don't see how you could do this in a hour with the coolant flush/drain time. My service took almost three hours because I got sidetracked thinking one of my hoses developed a leak. Everytime I poured coolant in the tank some coolant mysteriously appeared below. It turned out that the funnel I used allowed some coolant to flow out the overflow tube. This took me an hour to diagnose because I thought either one of the hoses had sprung a leak or the tstat wasn't seated correctly.

All is well though. The old tstat rubber seal clearly had failed. The new part was a different design. A bit simpler..... Thanks to all who helped.

Very doable DIY.

 

[Lonestranger]

Confucious say, "it's a poor workman that blames his Tool" :biggrin:

I finally replaced the thermostat yesterday. I don't see how you could do this in a hour with the coolant flush/drain time. My service took almost three hours because I got sidetracked thinking one of my hoses developed a leak. Everytime I poured coolant in the tank some coolant mysteriously appeared below. It turned out that the funnel I used allowed some coolant to flow out the overflow tube. This took me an hour to diagnose because I thought either one of the hoses had sprung a leak or the tstat wasn't seated correctly.

All is well though. The old tstat rubber seal clearly had failed. The new part was a different design. A bit simpler..... Thanks to all who helped.

Very doable DIY.

 

[Meeyatch1]

It is not too difficult. The thermostat for 1997 comes w/gasket.

P/N 19301-PR7-305 (list is about $32)

If you download the service manual it is pretty clear how to do it.

The short version:

Drain coolant
Remove air cleaner assy
Remove throttle body rubber bellows
Remove two bolts in thermostat housing
Change thermostat
Fill coolant
Test Drive
Top off coolant

Honestly the coolant fill is the longest part if you have not done it. You can search on prime, I have described it in detail at least once.

HTH,
LarryB

Is this procedure, or the parts requirement, any different for a 1994 model?

 

[rsevo6]

I am amazed by the fact that some NSX owners think a warmup period of 7-10 mls is "normal" as many NSX owners seem to experience this .

This only means that many NSX are driving around with defective thermostats thinking it is normal as many have this

It is not normal!!!
Temp gauge should start moving within 1 mls and be just below middle of the gauge scale in about 3-4 mls max.

I had 2 '98 NSX, both taking about 7 mls to warm up and both had a defective thermostat having the rubber ring in it bulging out.
The first time I replaced it, this took me about 1,5 hours, the 2nd time about 3/4-1 hour, so 3 hours is rediculously long
I did pinch off the coolant lines, to minimise coolant loss.

 

[Ski_Banker]

FWIW, my 2005 has never taken 7 miles to warm up. Maybe 1-2 (to be fully warm on temp gauge) when its 35 degrees F. 7-10 miles when it's cold outside sounds like something's wrong, unless the system is different between years.

 

[drew]

Slightly offtopic, but can the thermostat be deleted and ECU re-worked to think that it's in warmed-up mode for the correct A/F ratios?

Engine heat is the enemy of performance and engine life, so why not start with the cooling system?

Seems nobody responded to this question:

A cool running engine will destroy itself in no time. The wear between a cool engine and a engine running at its hot optimal temperature is on the order of several magnitudes.

More than 80% of your engine wear occurs when the engine is cold and *trying* to get to its hot temperature. If you could preheat your engine to its running temperature before it starts that would be optimal.

I don't have my engine books handy so I can't scan in the nifty graphs...but the tubes is telling me the wear is 6:1 (cold:hot).

Heat does destroy the soft parts, seals and sensors.

Drew

 

[Synthesis]

I am amazed by the fact that some NSX owners think a warmup period of 7-10 mls is "normal" as many NSX owners seem to experience this .

This only means that many NSX are driving around with defective thermostats thinking it is normal as many have this

It is not normal!!!
Temp gauge should start moving within 1 mls and be just below middle of the gauge scale in about 3-4 mls max.

I had 2 '98 NSX, both taking about 7 mls to warm up and both had a defective thermostat having the rubber ring in it bulging out.
The first time I replaced it, this took me about 1,5 hours, the 2nd time about 3/4-1 hour, so 3 hours is rediculously long
I did pinch off the coolant lines, to minimise coolant loss.

i have a 91 that has been dripping coolant for a while now.... looks like from the left side of the engine bay. do you think this could be because of a bad thermostat/thermostat seal??? it has started to leak a little more now.

i am currently in the process of changing a hose that i *thought was causing the leak, and i'm praying to god that fixes it.... but, if not, would it be a good idea to check the thermo? is leakage common with a bad thermo?

 

[OLDMNSX]

... looks like from the left side of the engine bay. do you think this could be because of a bad thermostat/thermostat seal??? it has started to leak a little more now. is leakage common with a bad thermo?

I have never seen a thermostat seal fail, not to say that it couldn't, but not likely. Have you checked to see if the bleeder on the tube next to the firewall is snug, or the bleeder at the thermostat housing? Look for dried anti-freeze in or around the nipple, or where you think that the leak is located. How old is your coolant reservoir cap? Have you checked the reservoir for cracks?

Brad

 

[RON98]

Seems nobody responded to this question:

A cool running engine will destroy itself in no time. The wear between a cool engine and a engine running at its hot optimal temperature is on the order of several magnitudes.

More than 80% of your engine wear occurs when the engine is cold and *trying* to get to its hot temperature. If you could preheat your engine to its running temperature before it starts that would be optimal.

I don't have my engine books handy so I can't scan in the nifty graphs...but the tubes is telling me the wear is 6:1 (cold:hot).

Heat does destroy the soft parts, seals and sensors.

Drew

really. wow. neat.

i just through the issue was oil viscosity when the car i cold thus the wear and tear. leanr something new on prime everday. :smile:

um... here is what you can do, put cardboard in front of 1/2 your radiator if there is no time to fix the thermostate.

i acturally used a pastic bag once for 300 miles. :wink: worked great.

 

[sptrader]

I changed my thermostat last Nov because of the slow warm-up time. It now takes 2-3 miles to be FULLY warmed up. (195deg) and that is at about 40 degrees outside. Warm air comes from the heater in about 1 mile, which is still slow compared to my old SC300 (about 3 blocks for heat) but a huge improvement.

 

[Yellow_Fever]

Ok guys I have a problem here. I just replaced my oem radiator to koyo radiator and put a new thermostat in but used the old seal. I filled up the tank with radiator fluid (I only used one jug) and left the car running for bout 5-7 mins. The radiator fan never turned on. The temp gauge was normal until I started driving the car. While I was driving around the gauge slowly started to rise all the way up to hot. So I stopped my car and checked the fluid. It was still at max. I checked if the fluid ran up front to the radiator and it did. I don't know what seems to be the problem here. Did anyone ever ran into this kind of problem? Can it be the oem seal? It's starting to get dark n cold out so I just parked the car. If someone knows the problem please let me know. Thanks in advance!

 

[nsxter]

Did you bleed they system?