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Bad thermostat

12K views 88 replies 13 participants last post by  PLT383 
#1 · (Edited)
I removed my VCM disabling device today and plugged my scan tool in to monitor the coolant temperature while I was driving today.

While idling after the engine was warmed up, the temp got up to 225. Is that normal? It hovered around 206-208 while driving. This was with no VCM disabling installed during this time.

The coolant level is good in the radiator and the overflow tank. I assume the only other thing it could be is a thermostat?
Any suggestions on how to further test this?

I should add, the fan does not come on when the temperature reaches 200+ which leads me to believe something may be wrong with the fan. Any ideas?

Thanks for you input.
 
#2 ·
If you're pretty sure it's a bad thermostat, just go ahead and replace it, since they're cheap enough. Less costly than a blown head gasket, anyway.

2006 HONDA PILOT 3.5L V6 Thermostat | RockAuto

Check, or actually just change your upper and lower hoses. I changed all that when I put in a new Denso radiator last year. I can't remember, have you ever changed your radiator?

Might also want to test your coolant strength. If you don't have a tester, they're also pretty inexpensive. I don't know why I keep forgetting to buy one whenever I'm at an auto parts place, but I should.
 
#4 ·
So to add something exciting to the story, I was sitting in a drive thru this evening and the gauge went to almost 3/4 of the way. As soon as I drove away, the gauge went back down. The more I revved the engine, the lower the temp got. I also noticed the fan's weren't turning on.

I'm not really interested in throwing a bunch of parts at it and I don't really have time to do it myself so I want to have some general idea of what is wrong before I go to the shop

Based off of this, would it point to the fans being the issue?
No coolant loss, no white smoke, just changed the oil and everything was good. The thing that confuses me, is the temp goes back down to normal ~206 degrees when I'm revving the motor.

The coolant was completely changed May 2020 when the timing belt was changed. Radiator is original as are the hoses.
 
#5 ·
Test your fans. Make sure they both come on.

The thing that confuses me, is the temp goes back down to normal ~206 degrees when I'm revving the motor.

Tensioner and/or water pump not doing their job? Assuming they were changed with the timing belt, who installed them and what brand were they? Not Gates, I hope.

 
#6 ·
I believe that the "open" temp for a Honda thermostat is 175 F. 225 F is too hot; so is 205. You can check the fan by turning on the A/C - it should be on then.

I think it's probably a flow problem. If everything else was OK, temp and RPM shouldn't move together so obviously. Since there's no fan, you're only dumping heat from the radiator without airflow.

My guess is that either the radiator is obstructed, and flow is improving when the water pump spins faster, or the water pump is binding / slipping / not turning like it's supposed to.

While I think that proactively replacing the thermostat and the upper/lower hoses is a good idea, I'm not optimistic this will fix your problem. Since you're not planning to chase it down yourself, I would get it into the shop ASAP and tell them what you've noted here.
 
#8 ·
My thermostat lasted 16+ years, not crusty but the seal to the block was compromised as well as the hose connection. SMH...disaster averted again. Not saying this is the issue but besides neglecting coolant maintenance, mixing in different types of coolant can result in a gel-like mixture. The gel-like mixture/coolant can stop normal flow through the system, clogs up passageways, radiator, and the heater core. Like everything else on my TLC I replaced the thermostat with a genUine Honda thermostat $$
 
#10 ·
Thanks everyone for your suggestions. Calling the mechanic shortly to see what to do next.
Let me just warn those who have VCM muzzling devices on their vehicles, it was much more difficult to detect while the device was on. So at this point I think it's very important to ensure you get a muzzler that cuts off if the engine reaches a certain high temperature.
 
#11 ·
Respectfully, I dont believe that's the answer. Ensuring our cooling system are functioning properly is. Then install a VCM disabling device.
Simple things we can do..
In the morning, on cold start, do the cooling fans come on when I turn the AC on? If not, you likely have a problem.
After a drive, knowing the engine is warm, when returning home, place the vehicle in park, turn the AC off. Observe whether the cooling fans are coming on and off to keep the engine cool. If not, there is a problem.
 
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#14 ·
Mechanic is saying possibly radiator or maybe the cooling fans.

No loss of coolant, white smoke or contamination leads me to believe it is NOT the head gasket but I'm not an expert. But I hope I'm right.
If the car
I removed my VCM disabling device today and plugged my scan tool in to monitor the coolant temperature while I was driving today.

While idling after the engine was warmed up, the temp got up to 225. Is that normal? It hovered around 206-208 while driving. This was with no VCM disabling installed during this time.

The coolant level is good in the radiator and the overflow tank. I assume the only other thing it could be is a thermostat?
Any suggestions on how to further test this?

I should add, the fan does not come on when the temperature reaches 200+ which leads me to believe something may be wrong with the fan. Any ideas?

Thanks for you input.
If it cools from 225F to 207 when moving, that looks like one or both fans aren't running when not moving. If you turn on the AC and go look, are they both running?

When the engine cools, open the radiator cap and let the engine warm up, check for flow when the thermostat opens, wait for the fans to come on. Make sure you see good flow in the radiator and there are no leaks or obstructions in front of it, like leaves, snow, dead bodies, missing $100 bills, etc.
 
#18 ·
Apparently it was the radiator and the fan. It's had a crack in it for a while and it wasn't causing a big enough problem for me to do anything about it. I kind of forgot about it.

So $700 for the fan and the radiator. Not ideal, but reasonable as far as paying someone else to do it goes.
 
#19 ·
Apparently it was the radiator and the fan. It's had a crack in it for a while and it wasn't causing a big enough problem for me to do anything about it. I kind of forgot about it.

So $700 for the fan and the radiator. Not ideal, but reasonable as far as paying someone else to do it goes.
Oh man!
We can walk you through a DIY, for way less than that with Denso.
 
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#22 ·
^^^ What he really means, and I'll say it because I want to know too, is was it a Denso? :p


Glad you got it fixed. The radiator can have a slow leak for quite a while before it opens up and outright pukes on you. Glad you caught it early.

The fans are the cause or coincidental? Get the old ones and hook them up to a battery, as suggested. While I think we're all happy it's all taken care of, some of us OCD PIloteers are itching to scratch beneath the surface. :)
 
#23 ·
The fan has wobbled for about a year but I think it could go longer before it needed to be replaced. It was shared labor so I decided to go ahead and replace it. I kinda figured I’d get one at a junkyard or something.

As far as what brand, I don’t know. I suppose I’ll ask when I pick it up but I don’t really want to know because people on here will make me paranoid it’s gonna fail again. 😂
 
#25 ·
Well I'm just floored by what I have found if you want a Denso fan for a 2008 Honda Pilot. Sorry, Denso and Honda can go out of business before I pay their extremely inflated price. 😡
146331

I can buy a TYC × 10.
146333
 
#30 ·
The fan was $100. I don’t know how much the radiator was. I will find out tomorrow morning.

I’d pay Honda prices for a radiator but probably not for a fan.
Honestly if I was going to DIY all of this, I’d buy a Denso radiator from Rockauto and pick up a fan at the junkyard. This fan works fine, it just wobbles a lot.
 
#31 ·
What I'd do: Denso radiator from RA (which is what I did, in fact), and a TYC fan assembly with the red heart icon from RA as well, installed with TLC.

 
#32 ·
Save another $50 and buy the TYC radiator. I've probably bought most of the brands on RA over the last several years with no issues. CSF, OSC, TYC, Spectra Premium. CSF has a limited lifetime warranty.
 
#71 ·
Any markings or part numbers on the radiator itself that you can see?
 
#83 ·
I have the same problem and it turned out to be the fact that I kept the temperature control system off you must have the temperature control system on auto with the AC on when the AC is on it will make the fan go off at 178° I leave the temperature control system on all the time it was told to me by a Honda Mechanic specialist
 
#84 ·
I was curious about how I will monitor this when I receive my VCM disabler. After searching how hot should a 2011 Honda Pilot engine run? I found this response on Google if it helps:

Once the thermostat opens the engine coolant temperature can run from 210-230 degrees. Engines are made to run a little warmer now than in the past due to emission control requirements. ... The normal operating temperature of the coolant in an engine is about 210F to 240F degrees.Jul 4, 2016.

I've had my Pilot for about 2 months. Drove great at the dealer and, of course, started having issues a few days later. Now that I've been driving it I can tell it's wearing on the engine mounts. Yay. Hope the disabler helps! I'm at 108K miles. Insert mad face and rolling eye emoji here
 
#85 ·
I was curious about how I will monitor this when I receive my VCM disabler. After searching how hot should a 2011 Honda Pilot engine run? I found this response on Google if it helps:

Once the thermostat opens the engine coolant temperature can run from 210-230 degrees. Engines are made to run a little warmer now than in the past due to emission control requirements. ... The normal operating temperature of the coolant in an engine is about 210F to 240F degrees.Jul 4, 2016.

I've had my Pilot for about 2 months. Drove great at the dealer and, of course, started having issues a few days later. Now that I've been driving it I can tell it's wearing on the engine mounts. Yay. Hope the disabler helps! I'm at 108K miles. Insert mad face and rolling eye emoji here
Hey there Hardy,

Thanks for posting that.

I've read SO MANY posts about these OCD people who buy a scan took and read their (actual/sort of) coolant temperatures. Then they somehow think that at ambient pressures, if pure water boils at 212F, then their Pilot with a coolant temp of 220F is running too hot! LOL I've seen it many times on this forum.
 
#87 · (Edited)
Man, this thread is getting weird......I had to force our G2 Ridgeline to reach these temps, then the efans turned on and coolant temp started to drop. Idling, a/c off, upper 90s ambient. I've been monitoring various temps in various vehicles using a ScanGauge since about 2005.......I don't recall seeing 210F-240F coolant temp, but if Google says so, then it's got to be true.;):poop:

What does the t-stat do????.....careful now.
 

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