Even with a hotter thermostat (82-deg C Motorad), I'm only seeing a ScanGauge reading of 202-deg F on days where the temp is in the low 90's. Yes, A/C on. I can't recall ever getting into the 230's Fahrenheit for ScanGauge coolant temp readings, even on 110-deg F days.

I'm wondering if the thermostat is starting to show its age. Many say thermostats are "wear items", just like tires, and I would tend to agree. I've replaced the thermostats in both of our Odysseys (2002 EX and 2003 EX), and they are due for another changeout in the near future. This month I the thermostat on the 2005 Altima we just purchased, and I've got an OEM Honda thermostat on my desk waiting to go into our 1998 Accord.

None of these cars had a malfunctioning thermostat. Given how hot it gets in SW Oklahoma (Africa hot), I like to put new thermostats in periodically before they stop working.

OF

P.S. I like the ScanGauge. I keep TPS (throttle position sensor) and coolant temp and fuel trims displayed, and if I'm really careful, getting 300 miles on a tankful of gas from just scooting around town is achievable.

 

P.S. I like the ScanGauge. I keep TPS (throttle position sensor) and coolant temp and fuel trims displayed, and if I'm really careful, getting 300 miles on a tankful of gas from just scooting around town is achievable.

I got the ScanGauge II for the turbo Volvo. Wanted to keep track of IATs since the car looses HUGE amounts of power in the summer. Turns out with the A/C on and 104F outside, I can see IATs over 145F without stomping on the pedal. Without A/C, in the spring/winter, IATs are only 4-6F above ambient temps. That' what surprised me so much about IATs on the Ody. They were pretty constantly 119F on the trip back, and in February, I was able to get a good idea of the outside temps b/c they were 20F below the IAT that was on the display. I bet there is a noticeable amount of power loss hiding in that 20F.

 

I would suspect the thermostat and/or a dirty/plugged radiator. If you turn the heat up to full hot and turn the fan on high (I know, nobody wants to do this but it's an old trick for overheating vehicles back when overheating was common) will it cool it down a bit?

 

6 people, an unwanted dog, 80 mph and 100+ desert air. Didn't even try it. Turned the A/C off for a minute to see the temp dip 6F or so. Thanks for pointing me towards the t-stat. I can go back and look at records, but I am pretty confident that if it was changed, its only been once, and more than 80-90K ago. OEM or will aftermarket Chinese units be as good?

 

I would definitely stick with OE on the thermostat. As for IAT's you have to consider where the sensor is located and where it's taking its measurement. It is located on the intake manifold so it's going to read hotter than ambient outside air temps. The factory intake already pulls in air from outside the engine compartment. Cold air intake setups really aren't cooler air since they pull air from inside the engine compartment. I've never figured out why people even bother other than they think they're getting better flow but in reality they're just messing with the smooth flow of air over their mass air flow sensor (which your Ody doesn't have.) Regardless, if the outside air is hotter then the computer has to reduce the amount of fuel to keep the mixture at stoichiometric. For unexplained low power I'd take a look at oxygen sensors in the live data and make sure they're switching as quickly as they're supposed to. If they have more than 100K miles on them I'd just replace them.

 

If you are going to change the thermostat and your coolant is long on years, then i would suggest that you do a radiator flush (your choice of chemicals), complete internal rinsing with distilled water (several times) and then put in a quality coolant designed for your Ody. Put new quality radiator hoses on at the same time. Be sure to drain the block each time also.
I would also recommend an OEM thermostat. I tried the hotter 182F Motorad (made in Germany) AFTER I replaced my radiator (cheaper one on Ebay) and found that I was running up above 208F - 228+F while doing 80 mph on a hot summer day (just a little above and below 100F ambient) on a 1000 mile trip.
Once a thermostat goes above its rated temp, it should be fully open and not really increase the top temp on hot days.
I removed that Motorad and put in an OEM and on the trip back, just as hot outside, the highest temp was 208F.
I tested that Motorad in boiling water, along with the old OEM and the OEM opened wider.
Still, since Odyfamily had better luck, I do believe it was the cheaper radiator that I purchased off Ebay that was causing the poorer heat exchange (yes, I also installed both new radiator hoses).
I contacted Motorad and they sent me another thermostat, free, and I tested it in boiling water, and it opened slightly more than the first Motorad, but still quite a bit less than the OEM.
So, with a cheaper radiator and a thermostat that didn't open as much as the OEM, my Ody was running too hot on that trip, BUT, my mpg was better with the higher coolant temp. Go figure! :ahh:
Buffalo4

 

BUT, my mpg was better with the higher coolant temp. Go figure! :ahh:
Buffalo4

oil got thiner.

 

Guys, I may be at the end of my experimenting with Motorad 82-deg C thermostats with the next thermostat changes, which I'll probably do this fall. We still have the two Gen 2 Odysseys, with 177,000 and 182,000 miles on each of them. With the last radiator drain/refill I did last year, I added 16 ounces Hy-per Lube Super Coolant to each van, and the amount of heat exchange we received at the heater vents on snowy days just felt a whole lot warmer than in previous years without it. The 82-deg C thermostats already made a huge difference in defrost capability during freezing rain and freezing drizzle conditions, but the Hy-Per Lube seemed to actually bolster defrost performance in a good way.

I think I will revert to OEM 78-deg C thermostats in both vans, and we'll see what happens with 50/50 Prestone, and Hy-Per Lube Super Coolant during our next snowy winter. If Hy-Per Lube doesn't help enough at helping defeat freezing precip with a 78-deg C thermostat, I'll report back.

Hy-Per Lube probably operates similarly to Red Line Water Wetter. They changed the packaging, to a different bottle this year, but the bottles I purchased last year appeared to employ weak organic acid compounds to give the coolant the qualities of a buffered solution, which promotes long-term pH stability (and ergo, corrosion protection).

OF

 

Odyfamily,

So the Hy-Per lube gave you a more obvious improvement - faster defrosting - than the hotter stat? But isn't the additive suppose to keep the coolant cooler than regular coolant? How does that translate to a quicker warmer heating? Maybe better flow?

My almost 5 year old 13 dollar AZ stat has been performing as it should. Last year I noticed the temp gauge needle move up a bit when the condenser fan broke. After I did the fan motor replacement, everything has been back to normal. I have no rush in replacing the stat yet.

 

I have no idea how it is doing this...or if coincidentally, my Motorad thermostats are starting to show their age and not open as much.

Essentially, no matter who makes them (Red Line, Hy-Per Lube, Royal Purple), these are just surfactants, also known as wetting agents. To give you an example, let's look at Windex window cleaner. It is essentially deionized water plus cleaning agents added in a small concentration. The big deal here is that if you spray it on a hydrophobic surface like plastic, the water will bead up, and not allow the spray to neatly cover the surface you want to clean. As simply as can be explained, a proper surfactant breaks the surface tension of the water, allowing the spray to spread more evenly and cover the intended surface.

How automotive cooling systems work at the interface between hot metals and moving coolant is one of those topics I never mastered. My basic understanding of this is that when coolant boils and creates a vapor pocket, the coolant around it collects heat, allowing the vapor pocket to immediately collapse. Common thinking is that assisting this vapor pocket collapse by adding a surfactant allows more efficient heat transfer to the coolant, where it then takes its load of thermal energy to the radiator. That is first piece of this puzzle.

The second piece, which I understand even less, is the interface between cooler surfaces (like the radiator's interior, or the cabin heater core interior) and the hot coolant. How the wetting agent helps with heat exchange at these surfaces to allow higher heat exchange efficiency is something I don't understand. I can understand how the engine's water jacket can pull more heat into the coolant, but how do these air-to-liquid heat exchangers (radiator & heater core) improve their efficiency with a surfactant? Anything I would offer could only be a guess.

This is also a guess, but I think this stuff can only help reduce peak coolant temp, all other variables held equal, only if you are always operating above the thermostat activation temperature in a thermally saturated system (i.e., with ECT readings over, say, 210-deg F on my ScanGauge, where the thermostat is fully open). Below those temperatures, I don't know how one could judge its effectiveness.

I'll find out this winter if Hy-Per Lube Super Coolant does what it says when I install the OEM thermostats. By the way, only use OEM rubber gaskets for your Honda or Acura thermostat. The ones by Stant are pretty thin.

The only, and I mean only, reason I'm using Hy-Per Lube Super Coolant is to see if I can go back to using an OEM 78-deg C thermostat in our Odysseys and still have enough thermal exchange between coolant and heater core to defrost my windshield. We'll see at the end of the year.

Even during Africa-hot days (like you get in Vegas), I've never had a problem with peak coolant temperatures in a bone-stock cooling system (just 50/50 Prestone and a stock thermostat), even with A/C running in stop-and-go traffic.

See this link comparing water wetters in a modified Honda Prelude: SuperStreet Online[/coor]

OF

 

When I try and go to that superstreetonline.com , my Avast Antivirus stops it and says:
Infection
HTML:Script-inf
Probably just a false positive. On virustotal.com, it says that site is OK with just one suspicious hit.

I would bet that when you put that OEM stat in, you will be missing that extra winter heat and defroster action.
I also put in the Motorad stat in just for the extra heat in the winter, but, I had to remove it before winter started. .
I know I would have appreciated the extra heat. :cheers: :ahh:
On really cold days, my engine temp is only around 170F or even a little lower.

Buffalo4

 

I would bet that when you put that OEM stat in, you will be missing that extra winter heat and defroster action...

...On really cold days, my engine temp is only around 170F or even a little lower.

Buffalo4

Man, I am hoping the Hy-Per Lube helps with heater core thermal exchange. ECT reading of 170F would really put a damper on the defrost action if the heater core efficiency isn't helped up a little.

Right now it's 94-deg F, going to be 102-deg F tomorrow. 202-deg F ECT ScanGauge reading with A/C on, stopped in traffic.

OF

 

I did notice that intake air temps ran considerably higher than outside temps.

The throttle body is heated to reduce icing in cold weather. It would raise the IAT but I can't say if the temperature rise would equal the 40 degrees F increase that you observed in high summer heat.

FYI, another member posted a simple mod to the plumbing to bypass the TB heater.

Dave

 

Interesting...did you follow the 30/70 antifreeze/water ratio? I wonder if you just add it to the standard 50/50 ratio, will it yield less or no impact - cooling power. Just don't know of the long term protection it will provide if you put less - 30% - antifreeze in there.

 

thaxman, I'll get a ScanGauge reading tomorrow. It'll be 102-deg F tomorrow, and I'll be driving at the height of the daytime temps in my burg.

nitely, I'm running 50/50 premix. I don't have any soft water with which to mix straight Prestone into a 30/70 mix, and I think it gets too cold in the winter in my area, so 50/50 is really safe.

OF

 

I am betting even stop n go, below 210F. I really think I am looking at a failing tstat

 

I viewed records all the way back to 06 when the trans went south. All I could find cooling system-wide was new hoses around 2008 and the t-belt/water pump etc @ 233K (I think 2013). No tstat unless it was buried in the t-belt line items somewhere.

 

This is weird. I must have had the A/C on low speed, so with little heat exchange, freon pressure wasn't enough to run the fans at high speed perhaps?

104-deg F today, you could hear the condenser fans roaring away with the A/C on...

...and the ScanGauge was showing ECT at 195-deg F while driving slowly, and stopped at the light behind another vehicle. I'm used to seeing numbers in the low 200's under these conditions. The only change in variables is my using a single bottle of Hy-per Lube Super Coolant.

I'm going to install another Moto-Rad 82-deg C thermostat into each van again, this fall. Buffalo, you definitely give sound logic for this course of action. You know, I'm remembering that the van sure seemed to warm up to "the heat really works now" temperatues a lot faster with the Motorad thermostat, versus the OEM thermostat which just never seemed to get off its hind legs during sub-freezing weather.

I will definitely test it (as you did) before installation.

OF

 

All of you are talking as if changing the thermostat on the van is as simple as changing the engine air filter. I am under impression that it is at least as difficult as *first time* changing the cabin air filter aka lot more painful.

 

Cabin air filter change (first time) is a little easier to do than a thermostat change, but not by much.

Thermostat change: first, almost too obvious to mention, but I'm going to....you should drain some coolant from the block and radiator, not all of it. The thermostat is almost at the "high point" in the cooling system. As far as I can tell, the highest point in the cooling system is the radiator filler neck.

Some coolant will still spill out when you remove the thermostat housing. The old thermostat may be "stuck" due to the rubber gasket, for lack of better words, bonding to the block.

Replace, reinstall thermostat housing, refill with coolant, "burp" the system as mentioned elsewhere in the forum.

________________________________________________________________________________________________

Last night I immersed an OEM 78-deg C thermostat and a Motorad 302-180 (82-deg C) thermostat into a pot of water, set a stainless K thermocouple probe into the water, and turned on the heat. As the temperature rose (at a rate of less than 0.1 degrees Fahrenheit per second), The OEM thermostat started to creep open at just over 176-deg F. The Motorad did the same at just over 184-deg F.

At 192-deg F, the OEM thermostat appeared fully open, the Motorad just a shade less. Above that temperature, both appeared fully open.

Only about an 8-degree F difference in opening temperatures, which doesn't seem like a lot, but from personal experience I can say it sure makes a difference in winter time.

OF

 

Did the Motorad look like it opened as 'much' as the OEM? Mine sure didn't, and I tried two OEMs and two Motorads. Course, at my elevation, water boils quite a bit lower than 212F. I can't even get to 198F.
I still believe my problem is with the cheap replacement radiator I bought off ebay. They,the radiators, should all have flow ratings, etc. on them!
If my hwy speed temps didn't get so high, I would definitely have kept that Motorad in my Ody. Temps in the mtns of Colorado get damn cold.
Buffalo4
PS: Yes, changing the thermostat is a PITA, overall, compared to the PITA cabin air fliter in my '03.

 

That Motorad sure did look like it opened just as much as the OEM.

I'm thinking your radiator might be the culprit.

The name brands I look for are Denso, Koyo or Behr.

For thaxman, if it ain't a thermostat on its last legs, maybe it's the radiator as well (clogged). I just hope it's not a pinhole leak in just one of several coolant hoses in the engine bay.

OF

 

For thaxman, if it ain't a thermostat on its last legs, maybe it's the radiator as well (clogged). I just hope it's not a pinhole leak in just one of several coolant hoses in the engine bay.

OF

240 miles, 3 straight hours. I highly doubt there was a leak in the system or I wouldn't have made it the whole way, esp since the temps creeped up within the first 30 miles. Low-flow in the radiator, well, that is a valid concern.

 

Thankfully, it's not a leak, then. If you keep up on coolant servicing, Honda-Acura hoses last a long time. They really do stand up well to exterior environmental conditions. The big enemy to coolant rubber compound longevity for radiator & heater hoses is electrolytic attack from worn-out coolant (coolant that can no longer maintain a proper pH).

OF

 

Just a quick 'Thank You!' to everyone on this thread. As the forum slowly degrades with many of our original thought-leaders moving on, it's refreshing to have a thought-provoking thread as this one going with some of our best veterans contributing!

 

Did the tstat/fluid swap last weekend. Took the van out for a 90-mi/90-min drive where I went uphill 2000' over 30 mi, to get to a spot where I could run uphill 500' for 3 mi 5% grade all at high freeway speeds in the mid-90s Fahrenheit. With the new OEM tstat I was getting 206F-213F on the long uphill grade, but I was also going pretty fast b/c I was "pushing" it. On the way back, the temps were more in line with what I would have expected: 197-206F but it was mostly a downward grade overall. The hill climb I attempted at 80 but some vehicles interfered so some of the climb was done at 70-75 and I got up over 220F, which seems a bit high. I was running AC the whole time but at some point there and back I shut it all off and saw no differences in water temps. Still seems a bit higher than I want. How to "burp" the system?

 

I "burped" our 2002 & 2003 by driving it onto some ramps on our slightly inclined (uphill) driveway, and ran the engine with the radiator cap not installed. Eventually, it got warm enough to open the tstat and push coolant (and air) through the radiator. As it "burped" out the air, the coolant level would drop a little, sometimes requiring me to add a dash of coolant. I even pulled on the throttle assembly to run it at slightly higher revs once in a while to push the coolant through with more authority.

While doing this, the fans were turning on, off, on, off, as expected. Eventually, all of the air in the block and heads migrates to the radiator via the top hose, and there it stays at the top of the radiator. As long as I had just enough coolant to keep the top of the core submerged in coolant, it seemed I was doing this correctly. I shut down, topped off, put on the radiator cap, and topped off the reservoir.

Yesterday was almost 107-deg F, and I drove east on almost level terrain for an hour at 70 mph, A/C on the entire way. ScanGauge said 198-deg F.

thaxman, I believe our Odysseys have two temperature sensors. One feeds the gauge, and the other feeds the PCM (and ergo, the ScanGauge data feed for that parameter I.D.). If the radiator isn't clogged, coolant is flowing, thermostat is doing its job....I'm wondering if it's a bad data feed.

For Buffalo4: I think I may have found an OEM 82-deg C thermostat! Acura p/n 19301-R8A-A00 from the 2013-2015 Acura RDX should be a drop-in replacement for our Odysseys.

Also, I would tend to agree with Buffalo regarding flow. I boiled another pot of water, dropped in my Motorad 302-180 and the Honda OEM tstats yet again, and it does appear that the Honda OEM tstat does have more cross-sectional area to flow coolant than the Motorad offering. I haven't had troubles with the Motorad unit, but for all those who want to purely stick with OEM, we all now have an option.

I may drop by an Acura dealership and see if the guys at the parts counter will "help a bro' out" and let me see one to compare to the Odyssey tstat. If it has identical dimensions, we may have a winner here.

OF

 

Wow, how did you find that? I will buy one, after further checking, and try it out.
How did you figure out that it would work in the '03 Ody.
I am impressed. :cheers: :ahh:
Buffalo4
PS: I may even try that water wetter stuff since I will have to add some coolant anyways.

 

The best way to burp it is to use one of these:

https://www.amazon.com/Lisle-24680-Spill-Free-Funnel/dp/B00A6AS6LY

And then follow the procedure in the service manual. It involves full hot and cold cycling of the front and rear systems.

 

John Clark, you are the man who has everything.

I forgot the obvious; turn on the heater to full hot when burping the system.

OF

 

Now if only I could find a high-flow Motorad (or another brand) thermostat that would work on my '03 Ody.
Here is a link to that model type: https://youtu.be/OSGLgUq3vtk
They claim almost a 50% increase in flow volume at wide open.
Now, if I can only find one I can use which is rated at 180F or close to that number.
Hotter in the winter for heat, defroster, etc and cooler in the summer when the temps go way up!! :cheers:
Buffalo4
PS: I think the condenser fan goes on at around 210F and the radiator fan at around 199F if the ac is turned off.