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View Poll Results: Will an engine over heat without a thermostat?
Nope! It will never reach operating temp 15 88.24%
Yes! Don't do it! You will over heat! 2 11.76%
Voters: 17. You may not vote on this poll

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Old 06-15-2021, 10:58 AM
MysticRob MysticRob is offline
327 Rambler
Join Date: Nov 26, 2019
Location: Boise, ID
Posts: 550
Originally Posted by rang-a-stang
Crawled under my truck with my shiney new petcocks, looked up, and saw my knock sensor plugged in on the driver side. (totally forget it was there) Then the passenger side is tucked up nice and high behind my starter. Yay! 2 petcocks I can't use!

TStat removed.

I would have driven it today but I have a bunch of stops on the way to/from work. Tomorrow.

Jeebus, you're such an experiment tease. Get on with it already.
1988 Jeep Grand Wagoneer / Baltic Blue & Tan
2008 BMW 535xi Wagon / Deep Sea Blue & Tan

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Old Yesterday, 12:25 PM
rang-a-stang's Avatar
rang-a-stang rang-a-stang is offline
Join Date: Oct 31, 2016
Location: Camarillo, CA
Posts: 4,176
Originally Posted by MysticRob
Jeebus, you're such an experiment tease. Get on with it already.
Hahahaha! Indeed I am!
************************************************** ********
Morning run complete. Some notes:
1) I met a buddy for breakfast so I was not starting from stone cold but it was cold. Less than a 5 min/2 mile drive, 90 minutes before the data run. I also left my hood opened slightly to allow it to cool a little faster than normal while we ate.
2) Run started about 8:25am and it was about 65 degrees out. When I got to work (about 8:55am), it was about 62 degrees (I work on the coast, live inland so it gets cooler as I drive to work).
Here is the chart:

Some observations:
A) It ran slightly cooler than the 195 TStat runs but not much. It took about twice as long to reach 185 but I was starting at 130. I assume if I would have started at 75F it would have taken much longer than twice as long.
B) I noticed a pretty big disparity between my digital temp gauge (what the computer is being fed) and my stock dash temp gauge. This has never been the case; they have always, generally, matched. My EFI Temp sensor is in the front passenger side manifold bung (where the timing CTO used to be) and the Temp gauge sender is in the factory spot on the front driver side so I wonder if the coolant flow from one cylinder bank is different than the coolant flow from the other when there is no TStat.
C) Almost every time I stopped at a stop light, I noticed temp increases. My fan is computer controlled and only comes on when speed is below 25mph and at a certain temp (I don't remember for sure but I think it was about 205 on and 195 off).
D) My Air fuel ratios (measured as BLM on my laptop) ran richer, almost the entire time. I expected them to be richer when it was cold but it seemed a little more than expected, even when engine temps were 180+.

Engine did not overheat without a TStat. It did run slightly warmer than normal on a few occasions but that was when only the fan was pulling air through the rad. Generally it ran a little cooler without the TStat. With the 195 TStat, it ran 197-205 while with no stat it's 195-200 with only 2 temp spikes. If the initial thought of "Coolant flows too fast through the radiator to shed it's heat" were true, I would think the times when I am sitting at a light at idle speed/fan on, would be the times when the coolant temp would drop the most since those are the periods when the coolant would be flowing through the radiator the slowest.
I will go home via 101 freeway tonight so we'll see if higher RPMs make a difference. It is supposed to be high 80's when I leave, too so that may also make a difference. I will also plan to run these runs one more time when my 180 degree TStat is installed next week and see if that really lowers my operating temp any. Since no-TStat is still operating at 195-200, I can't imagine a 180 degree is going to lower it much.

Full disclosure: I was totally gung-ho on this when it started. I am pretty nervous now! I really don't want to torch my engine! I am not worried it is going to create so much heat it will ruin a head gasket; more I don't know what the flow of coolant through the engine looks like without a TStat throttling it. For instance, is it just flowing into the block around cylinders #1 and #2, then up the head and out? How much coolant are #7 and #8 getting?
79 Cherokee Chief (passed CA smog check Sept 2020)
(Cherokee Build Thread)
11 Nissan Pathfinder Silver Edition 4x4
09 Mazdaspeed3 Grand Touring
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Old Today, 10:49 AM
rang-a-stang's Avatar
rang-a-stang rang-a-stang is offline
Join Date: Oct 31, 2016
Location: Camarillo, CA
Posts: 4,176
Highway run home complete.
1) Run started at 3pm and it was 73 degrees out. When I got home it was about 3:35pm and 80 degrees.

A) Temp disparity between my stock dash gauge and digital gauge was more evident during the "warm up" period. What it seemed to me was the stock gauge was 10-25 degrees below digital dash compared to normal. With my 195 Degree TStat in there, when the digital dash would show 200-205 (my normal operating temp) the needle on my stock gauge was almost straight down but slightly to the cold side. Last night, when I was 200-210, the needle was at the beginning of the green bar. That represents about 10-20 degree difference. Stock gauge was always lower than the digital dash.
B) I did not have any instances of knock retard during this run so my computer was not detecting much knock but I did notice as I got off the freeway around 27 minutes into the run, my oil pressure was slightly lower than normal and I think that is because my oil was hotter than normal. I have driven this route, under similar ​circumstances and temperatures, and have not noticed this happening in the past.
C) If you look at my temps from about 15 mins to the end of the run, it does look like there is a slight upward trend... I don't see that in the morning run and maybe that is because I was getting closer to home and the ambient temps were going up about that much too?
D) I also noted on the chart, there is an odd temp spike around 26 minutes and I do not know what it was from. It does not correlate to a change in speed or engine load. Hmmm...
E) "Warm Up" period (from 84-195F) was about 11 minutes.

Secondary Conclusions
Engine did not overheat without a Thermostat. Again, it did seem to run slightly warmer than normal on a few occasions and did have one unexplained spike but I do not see that as indicative of it going to overheat in the long run. I do have a strong feeling that the coolant flow through my engine was not sufficient. I believe (but do not have any data to back this up) that if I had a restrictor/orifice plate in there, it would run cooler than with no TStat.

Sometime in the next week or two, I will install a 180 TStat and data log the runs again to see what that does compared to the first set of runs. Glad this is over!
79 Cherokee Chief (passed CA smog check Sept 2020)
(Cherokee Build Thread)
11 Nissan Pathfinder Silver Edition 4x4
09 Mazdaspeed3 Grand Touring
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