v8 flathead temp. gauge goes up and down

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FROG_PONDS

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Just finished my resteration on a 40 pickup with a 47 v8 flathead. I installed a 160 thermostet in each rad hose at the head outlet. My problume seems to be the temp. gauge goes up and down all the time. I did replace both temp. sensors. The engine does not seem to be over heating but I did not run it for a long time yet. Has any body experanced this. Rich
 
Rich, To understand your readings, you must remember that the thermostats being closed when cold will force the temp quickly up to the range where the right side sender will indicate HOT, then with the rush of water through the open stats, the indictator will go down colder than normal for a short while, then climb back to normal running temp again. When stopped at a stop light, temps will rise again, which is also normal. There is something else to consider, that being the 160º stats in Pennsylvania. Your neck of the woods having extreme winters, your stats will open and close more often. You may have better performance and engine life by using 180º stats.
 
I live in the northeast upper part of NY State, 2.5 hours south of Montreal Canada. I have a '47 and had extreme readings showing on the stock temp gauge. The car never actually overheated. The dash gauge would show fast warm-ups, continue to go all the way to "Hot", then drop down to mid-gauge/normal, and behave normally after that. The left head also has a mechanical after-market temp gauge and that showed normal behavior and no overheating.

The car received a new radiator 10,000 miles ago and has good pumps and clean coolant. I changed the stats from 180 to 160 degrees and nothing changed. The engine heats up just as fast with the 160 stats as it did with 180 stats.

My erratic readings on the dash gauge were eliminated by dis-connecting and by-passing the stock two-terminal temp sensor on the driver's side head .... it already had/has a mechanical temp gauge anyway. NOW: The dash gauge indicator sits in the middle during normal highway driving. When driving up a long up-hill grade or sitting in traffic for long periods of time the indicator rises to about the 5/8 point - never more that the 3/4 point. It drops to mid-point after the car gets moving or returning to driving on a level road. Never shows below mid-point.

NOTES: (1) These stock dash gauges just give you a general idea. (2) Make sure wire connections are tight. (3) Install a mechanical gauge or better yet dual mechanical gauges if you want more accurate readings. (2) Some say running 180 stats heats the oil up higher and reduces sludge build-up. Personally, I use 10w-30 oil without a filter, change my oil every 1000 miles, and have not experienced sludge yet [35,000 miles on a rebuild].
 
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FROG_PONDS said:
My problume seems to be the temp. gauge goes up and down all the time. Rich
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Hi Everyone. Rich, they do this, with or without thermostats. And each car/engine/cooling combination is just a little bit different.

It's a bit of a stretch, but your experience is similar to what a commercial pilot experiences when he shifts between planes that are the same make/model but have different quirks (think Boeing 737's, there are a lot of them in a lot of different levels of repair). Among flatties, it's comparable to how they like to be started. Some want choke, some hate it. Temp is just the same.

Keep fluids handy. Check before each departure. Watch and learn how it behaves before changing anything. If you change something, do it one thing at a time. I've never known one to like a hard run, then a long idle, for example, but that's just me.

Monitor thermostats to make sure they stay in place.
 
FROG_PONDS said:
Just finished my resteration on a 40 pickup with a 47 v8 flathead. I installed a 160 thermostet in each rad hose at the head outlet. My problume seems to be the temp. gauge goes up and down all the time. I did replace both temp. sensors. The engine does not seem to be over heating but I did not run it for a long time yet. Has any body experanced this. Rich
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Hi all, my 2 bits worth. I had similar readings after installing 160 stats in my 33. Even after a long run, temp would fluctuate, confirmed with temp gun.
I installed another set of stats from the US and same again and engine took ages to warm up. After several new stat failures I purchased a couple of160 LOW FLOW stats and now the engine warms up quickly and also runs at a steady temp over a long trip. My thoughts are the high flow stats opened when hot and let too much flow through of cool coolant.
Maybe this is not what others have experienced but it has solved my heating problems I'm now happy that the engine is not getting hot & cold on a trip. Also a lot of help from mate Lawrie
Kpar
 
Thanks all so far. Let me explain a little more. When I say the gauge goes up and dowm I mean it goes to hot then down to very cold then back up to hot. It is like I have a bad connection but they all checked out ok. I do not know if I have a high flow stats in or not. I am going to try to disconnect one sensor and see what happens. I do have a new 3 core rad and all new wiring but stuff still happins. As you all know your first start up and ride is sometimes a disaster. Everything has to work. Thanks Rich
 
OK -- I went out and eliminated the double pole sensor and ran the engine till it was hot. Now I have no reading at all. I reconnected the double pole sensor and I am back where I started. Is it possible that the single pole sensor is bad and making the two sensors work together bad? Thanks Rich.
 
Are you sure when you removed the wires to the double pole that the single was wired in correctly (the two removed wires connected together)? I'm sure you understand how their connected, but just to cover all the bases.
 

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JSeey-- I do understand the wiring but is is a good idea for me to make sure that I have it correct. I will check my wiring. It not like I never made a mistake before. Thanks Rich
 
Yep, I hear you there! It is just odd the way you reported it. The two connector senders is just a pass-through connection in the normal mode. It only comes into play when the point open when it detects an overheat condition and the gauge goes to full hot. With the external connectors connected together it is out of the picture.

If it is behaving as reported then the single connector sensor wouldn't be working at all and the two connector sensor would be opening and closing at a lower temperature than it should be.

Two things I would recommend, hook up a separate temperature gauge to see if it sheds light on what is really going on and/or get an IR temperature detector and check the temperature at the outlet of the head.
 
OK -- the wires were crossed, it seen to have seteled down and working. I will take it for a ride later and see for sure. Thanks all Rich.
 
Let us know what happens. Doesn't sound like its your problem but I have a spare working dash gauge if you need it.
 
OK-- I took it for a ride today and it's back to where it was. The temp gauge went up to normal then down to (below cold) all the way to the left, then it went up to 3/4 and then back down. Rich
 
Remove the stats and see how it looks. Take temperatures on both
head outlets with the engine running at about 20 MPH speed with a
laser pointed thermometer. Sounds like the stats restrict the flow. G.M.
 
Put a cliplead across the 2 wire sender or just connect both wires at one terminal.
If the switch opens at a to low temp you get a reading jumping between normal and overheating.
If it works at it should bypassed replace it.
 
The first thing I am going to do is try a lazor pointer that I gust picked up to make sure it is not overheating. I did try bypassing the double pole sensor before by connecting both wires on one terminal and I got no reaing at all. I am going to remove the thermoststs and try it without them and then replace them if needed. Thanks Rich
 
FROG_PONDS said:
I did try bypassing the double pole sensor before by connecting both wires on one terminal and I got no reaing at all.
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That would indicate that the temp sender is not working at all (the single connector sender). As you already know, the two connector sender is just an on/off switch. Think the heat gun is a good test to run.
 
No reading at all meaning it goes to cold or stays at hot ?
If you bypass the switch you should either get hot(open), cold(short) or a reading in between that at working temp...
 
OK- The lazor gun tells me the engine is not overheating. I removed the thermostates and it is still the same. I ordered a new single pole temp sensor and when I test that I will let you fokes know. Thanks Rich
 
FROG_PONDS said:
OK- The lazor gun tells me the engine is not overheating. I removed the thermostates and it is still the same. I ordered a new single pole temp sensor and when I test that I will let you fokes know. Thanks Rich
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What temperatures did you get on EACH side on the head just below
the radiator hoses? G.M.
 
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