Thread: Puzzled over temp sender location

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When I put my T together I put the electric water temp sender in one of the threaded holes in the back of my intake manifold. The intake has four different places I could have put it...........there is one in each corner of the intake.

Ever since I got it running, the temp gauge never went above 120-130. I kept feeling the upper and lower hoses and the top one is pretty warm and the bottom one was less so, and I could usually keep my hand on it. I am running a 160 thermostat. Even on a trip or in stop and go traffic it never got higher than that.

So the other night I moved the sender to one of the front holes, and now it comes up normally. I let it run for a long time and it got up to 180, and as soon as I turned on the electric fan it dropped to 150 in about a minute. Then I drove down the road for about a half hour and the temp never went above 150, and I believe that to be correct because my hoses are only fairly warm, not really hot to the touch.

My question, why did the sender read so cool in the back of the engine? The sender was getting water there because when I removed it water poured out. Is the back of the engine so much cooler than the front?

All in all, I'm not unhappy with the temps it is running at, I guess the aluminum radiator and high flow water pump are doing their jobs, but just curious why the difference. Oh, yes the gauge is matched to the sender, they are the same brand and are made to work together.

Don

Don the only thing I can think (and this is a stretch....) is that in its first position at the back of the intake manifold, it was on the supply side of the coolant and had not had as much of a chance to transfer a lot of heat yet into the coolant as it came in from the radiator. And when moving it to the position you did in the front put it on the return side just before it exited the motor on its way to the radiator, which would allow more time for the motor to dissapate heat into the coolant and therefore cause a higher reading.

Like I said, it's a stretch; but, until I can come up with some other strange reason, that would be my best guess....

Cheers,
Dutch

Coolant flow and heat dissipation works on a perculation theory. Gaskets are perforated to control flow from the rear to the front of the engine. Therefore you see a varied range of temps from rear to front. Heat has all of it's generation at the cylinder and then the coolant has to control head temps by flowing through them and theoretically keep an even base before it hits the radiator. Not perfect by any means but as the years of research between racing and everyday driven cars, the manufactures have compromised the best perculation and flow technology they can for the average applications. You will always see a cooler temp at the back and hotter in the front unless you have a weird problem.

What surprised me the most was the wide variance between the front and back. My gauge starts at 120 and most times it wouldn't get off of that. Now it comes right up to the proper temperature since being relocated. The gauge is brand new and so is the sender, so they should be accurate. I also know the engine wasn't getting too hot because the puke tank never changes as far as water level and the hoses are fairly cool to the touch, at least you can hold your hand on them and not get burned like in my daily driver.

Don

That's another concern Denny. I have a 160 in there, but the engine runs at 150 going down the road. I know the thermostat is opening and closing because I can feel the top hose warm up when it opens. I am getting some blackening inside my headers, so it is possible it is running too cold.

Don

Denny and several others have stated before that proper heat into the system on the cooling side id important. Proper combustion is most effiicient between 180 and 220 degrees at the coolant side of the operation. PCV and total control of burn rates operate more efficiently at these temps. Temps within the rest of the engine are a concern also but for the guy whom wishes to just have a good ride and enjoy, keep the coolant levels (temp) where you know where it likes it. I replied because you posted a good question of why such a difference. You're good to go.

Originally Posted by nitrowarrior

You will always see a cooler temp at the back and hotter in the front unless you have a weird problem.

Huh?? I think that's backwards... On a conventional small-block Chevy (which Don has and I also have in my coupe) the water pump pushes coolant directly into the front of the water jackets. By the time that coolant makes it to the rear of the block it is VERY HOT! If you notice where GM put the temp sending units in Chevy engines, it is either in the front intake manifold water passage or in the left head between #1 & #3 cylinders where it sort of reads an "average" temperature. I made the mistake of putting the temp sender in the right head between #6 & #8 when I first got my coupe running and the temperature went up and down like an elevator. It was always reading between 210 and 260 with a 160 thermostat! I changed hoses, water pump, radiator, thermostat (twice), and the fan; nothing helped. Finally a friend of mine spotted the problem right away - he said "move the sender and your problems will be solved". He was right.

HHmmm.....you maybe right. Drill a hole for your distributor and re-install your intake backwards. Then, you'll get the reading you thought was supposed to give as stated. I see where you're going with this and as we all started in this feild, that seems to be normal. I gave the layman's terms for theory and why the people you buy gaskets from produced the items the way they did. If I was smarter than they are, I'd be making their millions. Too many years of them trying to stay competitive in their field has created what you buy from them. They did the leg work and I don't always second guess why they did it. It's their theory.

No, I certainly appreciate all of the answers and am not discounting any of the reasons, I hope anything I said wasn't misconstrued as being ungrateful for the responses I got. What I am trying to determine now is if I should go to a higher thermostat to get the temp up a little. This is a strange one for me, because in Florida we NEVER have a car that runs too cool, just the opposite. Plus, I could see a minor variation between the front and back of the engine, but 60 degrees is a huge swing.

What I may do is see how the car does on the trip to Billetproof and then change to a 180 after that if the temps stay too cold on the road. I just thought of something else. I am taking a job at a marina probably within the next week. My friend Craig is the Service Manager there and has one of those infared guns, I could have him shoot the entire block, looking for what the various temps are all over the block surface.

Don

Don, as I said, you're good to go. My response in the last case was not for you. If you feel the need though, step up the T-stat a few degrees. for complete all around performance. It's not unusual or uncommon that the differences of front to rear be that big. You have a system that works. Run with it and thanks for sparking interest in why, when ,how, etc. Enjoy the ride.

Don
good thread. Soon as my rewire is done, on goes the aluminum manifold. Nice to know that sender placement will affect temps!

Nitro, I'm not trying to stir up a big flaming argument here. I didn't think I had, but after re-reading my last post, maybe I came off a bit too abrasive. I appreciate your explanation of the theory, but was just curious if you possibly had stated it backwards...

Years ago Smokey Yunick did a bunch of work on Chevy small block cooling systems. One of the things he discovered was that, because of the way coolant circulates in the engine (block first, then forced through the heads), cylinder head temps were uneven and erratic, especially the rearmost cylinders. The trouble with that is one or more cylinders may be at optimum operating temps while some others are too cool and still others are melting pistons. It's not a huge problem on the street; we just cool the hottest cylinders enough to make them live and the others survive just fine. The temperature that we read at the front of the intake or the front of the head is an "average" of sorts. In a radically built race engine, though, they want all cylinders at optimum power efficiency all the time. The way Smokey finally did it was to reverse the flow and cool the heads first. It dropped cylinder head/combustion chamber temps so that he was able to boost the compression ratio higher yet and still maintain optimum efficiency temperature in all 8 cylinders. The latest version of the Chevy's V-8 has reverse cooling...

All this still doesn't answer your original question, Don. Even if the sender was just reading the temp of the metal of the intake with no coolant circulating, it should have been more than 120...

I have that book as well and my list goes on. I don't think you ruffled feathers. I agree with the fact that coolant flow is not perfect nor can be with today's engine configuration. It is as good as the everyday buyer of parts can make it with the parts available. Therefore what is on the shelf is what we use and Don's curiosity brought up a good point of why the difference.

Hey guys, I found the problem. I had the sender screwed into a vacuum port.








(that was a joke )

Don

So, did it give you a good temp reading of your vacuum consumption?.....