Which temperature gauge to trust? Or, how hot is too hot?

First: 3.0L EFI here.

I replaced the water pump a couple weeks ago. I noticed the engine temp was a little high the other day (near 220, according to the dash gauge), so I bled the system at the radiator, which I forgot to do last time (I have a self-bleeder at the water pump).

Today it was running a bit hot about, about 7/8 of the way to 220 from the unlabeled tick. But this time I had my laptop — TunerStudio showed 201 degrees. This was at highway speed (around 70 MPH in this case). It was 82 out today.

So, which gauge should I trust? MeagSquirt is reading from a sender mounted on the water pump, while the gauge is still using the original sender location on the back of the cylinder head (I think). Or perhaps both gauges are correct, since they’re measuring different locations?

I bled the radiator again when I got home. There was a hiss, some steam, and then coolant after a second or so, so it looks like I still had air in the system, assuming I’m reading that right.

I consider 220 to be too hot. I know it’s not a red line, but I’m paranoid from overheating issues in the past with the old engine. I also have a 2.5 hour trip each way next weekend, so I’d like to rule out any high temperature issues before then.

Any advice is appreciated. Thanks!

— Joe

And here are some pics of the gauges that I took while on the road. Apologies for the quality.

— Joe

https://uploads.tapatalk-cdn.com/201...f6d7544e60.jpg

https://uploads.tapatalk-cdn.com/201...1d82863a3b.jpg

The correct sender is very critical to have the gauge read correctly. I did some sender testing and I did get three senders reading the same. The gauge like most old automotive gauges compensate very well for car voltage changes.

I will look for that thread I did for the sender results.

Post #37 has the sensor values for temps. Other posts in that thread also have gauge testing

http://dmctalk.org/showthread.php?15...tterstat/page4

All of the factory gauges should be considered rough estimates. They're indications will change with battery voltage, ground condition, etc. Trust the Megasquirt gauges more!

Has either one been calibrated? Procedure to do so is in MS instructions....

If you're feeling enterprising, there are also methods of implementing AC control through megasquirt which can shut down AC in an overheat condition.

BUT look at your gauge RPM vs MS RPM. The original gauges really are rough estimates.

You should check your gauges against an infra red non-contact thermometer. Where the sending unit is makes a difference and they could be off a few degrees. The place to check is the pipe the "O" switch is in once the thermostat opens.

Sorry for the late reply; I missed the notifications:

I've bled the radiator five times now (I get home or to a parking lot and bleed it). Each time there's a hiss of air before the coolant comes out. Thankfully I have the DPNW valve thing that you can just turn to bleed, rather than having to remove the hose, so it's pretty easy to do. I don't appear to have any leaks and the coolant level looks fine in the bottle, but each time I bleed it the engine temperature seems to get lower at highway speeds according to the stock gauge. Today, it was reading not too much higher than the mark between 100 and 220, and TunerStudio was showing about 197. This was about 10 minutes of highway driving, and it's about 80 degrees out and sunny.

I'm not sure if either sensor has been calibrated. I don't know how I'd calibrate the one for the stock gauge. My notes say I'm using the stock 2.8L sender in the head (the 3.0L sender was DOA). I'm guessing that the coolant temperature should be about the same for most engines, and that it isn't just that the 3.0L runs hotter than the 2.8L.

My note also say nothing about having calibrated the water pump sensor, so it is quite possible (re: likely) that I didn't. I feel like it was on my todo list and I forgot to actually do it. Once the car cools down I'll check the MS manual and see what it says to do. The fans are turned on by this sensor (and they do work), but if the head sensor is the right one it would mean that I'm letting it get too hot before the fans turn on. It looks like they're off by about 15 degrees -- the gauge reads a little over 220 when MS reads about 205.

I do tend to trust the tachometer in MS over the stock gauge, although they look reasonably close to me. That said, I haven't tried having the car sit at 1000 RPM and comparing the two either, so they might be more off than I think they are. I should do that sometime. Eventually I'm going to do that digital dash I keep threatening to do and then MS will be my only gauge.

I plan on adding AC idle up, once I add the circuit to my MS II hardware (next weekend I'm taking a 2.5 hour drive each way, so I'll do it after that). I didn't think of shutting off the AC if the engine gets too hot. I'm working on touch-screen climate controls as well; maybe I should have it turn the heater on automatically in those situations as well (my software could turn off the AC too, I guess, but I can't increase the idle when the AC is on, so I'll have to do the MS mod no matter what).

I have an IR thermometer, so I'll warm it up and see what it reads at on the otterstat pipe.

Thanks everyone!

-- Joe

I just did the IR thermometer test. I had trouble getting a good reading off the shiny otterestat pipe. It would read around 165-175, but it would be over 200 if I moved the thermometer body too close to the engine bay so that the waste heat from the exhaust system would interfere with the sensor.

I got a more expected 190-195 on the hoses at the water pump. The MS gauge would read 195-205 during this time (the fans were coming on and off, since I have them set to around that range). The gauge in the dash was reading a few needle widths under 220.

Here's a picture of where I took my samples.

Attachment 60859

Thanks!

-- Joe

I finally pulled the coolant sensor from the water pump and calibrated it. The boiling water test got 190 ohms at 200-210 degrees; I'm a little fuzzy on that because the meat thermometer I was using would change depending how far I put it into the water, and an IR thermometer was useless as expected in this context (198-208, aimed at the sensor through the water).

Ice water came out to about 9330 ohms, and room temperature (about 75 degrees) was around 3100 ohms. I plugged these into TunerStudio and it consistently read about 5 degrees cooler than the GM settings I was using. I decided to set it back to GM, because I'd rather have it read too hot than too cold, and I'm not totally confident that I did this right. It'd be nice if they printed parts numbers on these things and provided datasheets with the temperature curves...

I went for about 20 minutes of driving on the highway; it's 81 degrees out and sunny today. Engine temperature in TunerStudio ranged from 198 to 202 when in the 70 MPH range, during which the stock gauge was up around 3/4 of the way between the first unmarked tick and 220. It only got higher than that when I turned off the A/C on surface streets and go stuck behind a slow truck (around 20 MPH); TunerStudio went up to 207 and the stock gauge moved 7/8 of the way to 220. It cooled back down after the fans came on, and went back to around 198 when I was driving at 35-45 MPH.

One other thing is that I forgot to put more coolant in after bleeding the at the radiator, which was now sitting at around the level of the hose in the back instead of half full. Once I topped it off, subsequent bleeds almost immediately dumped coolant with very little air.

So I guess this is just how hot my car runs, or that the gauge just reads 10-15 degrees hotter than TunerStudio. Tomorrow is my 2.5 hour drive (primarily highway driving), with another 2.5 hours back on Sunday, so we'll see how that goes. The temperature was pretty stable on the highway today, so I don't think I'll have any problems.

Thanks!

-- Joe

That's how hot they all run. Go and fix some real problems :D

Here's some of my data from 90+ degree days last year:
https://imgur.com/a/soFILjN

Sounds good to me! I have to get better at using those graphing features. I was concerned about getting up to 210, but you were up to 217, so I guess I have nothing to worry about.

I made it from MA to the other side of CT with no problems yesterday. It was in the high 60s when I left in the morning, and ended in the mid 70s when I arrived. The engine temperature started around the 192, and got up to about 198 for most of the drive. It spiked to 202, at one point while going up a steeper hill on the highway, but went back down to 198 soon after. I was running the A/C pretty much the entire time, too. Nothing else on the car went wrong. Now I just need to get home. :)

The only remaining issue is the the belt squeals when I turn the A/C on. If I click it off and on again it fixes itself. The belt is probably just a little loose. I replaced the belt and one of the adjustment bar bolts (I'd stripped it), which fixed a much louder and more consistent squealing under much less load, but it looks like I need to tighten it up a bit more (maybe it stretched a little?). I have the old belt in the car just in case it breaks on the ay home.

Thanks!

-- Joe

I actually remember that 217 event. Open the graph again and look at the MPH in which 210 degrees was exceeded.

I had set MS to not engage cooling fans above 40MPH which seemed to work well. Then I got stuck behind a semi going just a little over 40. AC on full blast. Temp gauge starts going up up up. Drafting this truck seemed to really cut down on airflow through the radiator.

In short: I disabled speed-based cooling fan cutoff. But going to 217 didn't break anything :D

I have the high-efficiency cooling fans, so I decided to let my fans run normally all the time. I made it home today with no incidents, even with getting stuck in stop-and-go traffic for a bit (high 70s/low 80s and sunny today). The temp stayed below 209 the entire time. Oddly, it seems to run most hot (save for when stuck in traffic) at 65-80 MPH, getting to around 202. Going faster than that would drop to around 195, and between 30 and 65 would be more likely to run in the 195-200 range. I'll have to load up my log and see what that looks like in graph form.

Now that I'm home I'll be modifying my MegaSquirt II for A/C Idle Up support (J10/J11 to SPR3/SPR4) -- at the moment I have to turn the A/C off in traffic for fear of stalling at the moment, but at least it starts right back up again.

-- Joe

are you using the coolant temp sensor i sent you (for ms)?
It xrefs to a late 90s saturn, but it uses the same data as the generic gm sensor.

https://www.bmotorsports.com/shop/im...ance-chart.gif


In short, trust ms not the dash gauge. It has lied to me many times.

Yup, that's the one I'm using. I was pretty sure it was a GM, but I didn't see anything about it in my notes. Thanks!

-- Joe

Quote:

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Originally Posted by jangell

Yup, that's the one I'm using. I was pretty sure it was a GM, but I didn't see anything about it in my notes. Thanks!

-- Joe

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https://www.rockauto.com/en/moreinfo...LKbA95lA%3D%3D

I live in Columbia SC and unlike those who garage their cars during the winter, I rarely drive during the summer. Once that SS and motor heats up, that 80s a/c will keep you alive but thats about it. As a general rule, if it is above 85-90 and sunny I don't drive it. FYI my temp gauge has ALWAYS read what yours is showing. I would imagine that after 12 years the motor would have melted if that was to hot so like the gas and alt gauge I take them as a grain of salt. This summer has been very brutal with weeks of 100 degrees nonstop. I have a upgraded radiator and 2 bleeds, one at the rad and one at the engine. I have just accepted my D hates the summer and is a fair weather car.

This weekend I drove it about 20 minutes on the highway. It was sunny, humid and in the mid to high 80s. I didn't have my laptop with me, so I had to rely on the stock gauge. It very, very slowly crept up past 220, but not too far past, mostly because I happened to get off the highway at about that time. It came back down after that, again slowly. I'm guessing this have been around 205-210 on the water pump coolant temperature. I'm curious how high it would go before it leveled off, assuming that happens before the engine overheats. If it gets up to 215 (on the water pump sender) and holds there, I guess that's fine... On the drive home it was better, staying a hair under 220 on the stock gauge, but I think that was because it got a bit more overcast. I was running the A/C most of the time as well.

The coolant bottle is still more than half full, so I'm not losing coolant. I didn't think to bleed the radiator again, but really I shouldn't need to at this point. We're having another hot week, but I don't have any highway driving to do, and hopefully the fall will come early and I won't have to worry about the engine temperature as much until next year.

I also had the car stall on me at a light just before it turned green. I wasn't able to get it to stay runnign until I pressed on the gas while starting (at which point the light had just turned red -- the cars behind me loved that). Not sure what was going on there, and of course I don't have any logs from it. I'm going to start another thread about my issues with stalling at idle once I've gathered some logs. I can get it to happen just sitting in my driveway and shifting from R to N to D and back (but not always), so I should be able to get something sooner than later.

-- Joe