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HOT RUNNIN' CAR... or is it???


Robert Smith

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Well, over the weekend, I noticed that my gage was showing me that the thermoustat was playing russian roulette! It would wait till it got very hot... about 212... then the needle would slowy creap back down to 180 and then, when I was driving a long distance on a cool day or cool evening, the temp gage showed that I was at 200!!! To me, that's a little too hot for this car to be running when it's about 55-65 degrees outside.

Well, I had the thermoustat changed out... figured that was the problem... well, I put a new one in... a 180 thermoustat is what the book calls for so, I have one put in... driving home from my friend's garage, (going only four blocks) I see the temp go from 100-200 in a matter of minutes! As I pulled into the driveway, it was at 212!!! I turned on my heater and stepped on the gas a little so it'd cool off a little... it did, it dipped to 200 or so... just great! On my way to work today, I drove 3 blocks ( I live very close to work) and that temp gage was showing that it was at 212 again! Well, the car was running perfect, it wasn't acting like a car that was 212... I popped the hood, I got out and checked to see if I was getting any water spitting out of the radiator... there was no steam, no hot watter hissing... the car was running cool... just as normal as it could be... so, my guess is that my temp gage is flat out lieing to me... I'm sure it is, I know how a car acts when it is at 212! Doesn't act this nice hahahahaha.

So, any idea where I could land a good sending unit or working gage?

=R

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Is it really? I haven't really looked too closely under the dash... try not to spend too much time under there... it's not the most comfortable place to sit in my car... HAHAHA:D

For fun, here's a photo of the p-15 and I... her name is Genevieve... and this shot was taken just a few weeks ago in San Pedro where Santa Fe 3751 was parked for a rail fair... that thing was full of steam and blowin' it's whistle too! Amazing!

l_6c65f247fcca51ce29491220a447ac29.jpg

Ok, the fun is over... back to the question at hand.:D

=R

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Hi Rob. Have you read Tod Fitch's article about temp gauge repair...I think its in the links of the forum. I was fortunate to purchase some time back a n o s temp gauge for a 41 Plymouth. On that one, you can simply swap in the face of the P15 gauge and all else should be OK. The cable on the older one seems a bit longer than the P15, but just looped it under the dash.

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No, I don't recall that... I'll see if I can dig it up in my spare time.

If I'm going to pull out the cluster, I might as well put out the APB on a speedo... hahahaha! Or at least get the original rebuilt.

=R

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Don't pull out the cluster yet. If the dash gauge is reading anything then it is highly likely that the bulb/capillary/dash unit are still sealed. And if so, it is pretty likely that they are reading correctly. (Not much to go wrong with the system and still have it read at all.)

So with that in mind the first check would be to see if you really are over heating. I'd use an infrared laser temperature gauge to check various spots on the engine and radiator. But that is because I have one. :)

You can also use a conventional thermometer in the radiator.

From what you say about the symptoms it is possible that the engine is cool over all. Once you assure yourself of that then the question would be: Why is the back of the head getting hot? Best bet would be poor circulation in the block. But that is getting ahead of ourselves.

So run the car until the temperature gauge shows that 200 degree Fahrenheit number. Shut it off and check the radiator coolant temperature and also see if any part of the engine seems hotter than any other. Once we know that we (members of this forum) can suggest a reasonable next step.

P.S. Nice photo!

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Robert,

You could stick a thermometer into the radiator when the gauge is reading 200 to see what it really is. It may be a few degrees cooler in the radiator and hotter at the rear of the engine though. You can also pick up a cheap aftermarket gauge at Walmart or other store as long as it is a mechanical one with the tube. It may say for 12 volts on the package but pay no attention to that. That's just for the light bulb to light it up. You don't even have to connect the bulb wire to it if you don't want to. If you want it to light up go to the hardware store and find a 6 volt flashlight bulb to match the one out of the gauge, then you can hook up the light and it will work in the car. I've had one of those gauges in my coupe since my engine rebuild. Have an extra good original gauge but I think the aftermarket ones are more reliable then the old ones are.

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Robert' date='

You could stick a thermometer into the radiator when the gauge is reading 200 to see what it really is. It may be a few degrees cooler in the radiator and hotter at the rear of the engine though. You can also pick up a cheap aftermarket gauge at Walmart or other store as long as it is a mechanical one with the tube. It may say for 12 volts on the package but pay no attention to that. That's just for the light bulb to light it up. You don't even have to connect the bulb wire to it if you don't want to. If you want it to light up go to the hardware store and find a 6 volt flashlight bulb to match the one out of the gauge, then you can hook up the light and it will work in the car. I've had one of those gauges in my coupe since my engine rebuild. Have an extra good original gauge but I think the aftermarket ones are more reliable then the old ones are.[/quote']

Nice tip Norm, I have an aftermarket gauge in my p15 and it works great. Never thought of getting a 6v flashlight bulb so I can see it at night. I always just turned on the interior light to check.

I do agree though this would be a good, but inexpensive way to check the accuracy of the temp gauge. I think I got one from Wally world for $10-$15.

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Those are good ideas guys, I will take the car over to my mechanic who will run a temp test on the motor and radiator after work... I'm really wondering what it could be... do you think that the 180 thermostat is the wrong one? Should I have a 160? I touched the radiator when the temp gage was reading 212... I could keep my hand on the cap and other parts of the radiator for more then 10 seconds... and I also touched the block and seemed to be a normal running temp.

I'm not keen on using an aftermarket temp gage... good idea but, I'm a purest... I want to have the original.

=R

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As Tod suggested you need to check more than just the temp of the water in the radiator. With these hand held infrared thermometers you can check the temperature of all parts of the engine and especially the temperature of the sending unit right at the head to see if your dash gauge is tellin the truth or not.

Besides, they are fun to play with and you will be wondering how you've lived without one all these years.

http://cgi.ebay.com/ebaymotors/9V-Auto-INFRARED-Thermometer-Gun-Laser-Non-Contact_W0QQitemZ300108027036QQihZ020QQcategoryZ43991QQrdZ1QQcmdZViewItem

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Those are good ideas guys, I will take the car over to my mechanic who will run a temp test on the motor and radiator after work... I'm really wondering what it could be... do you think that the 180 thermostat is the wrong one? Should I have a 160? I touched the radiator when the temp gage was reading 212... I could keep my hand on the cap and other parts of the radiator for more then 10 seconds... and I also touched the block and seemed to be a normal running temp.

I'm not keen on using an aftermarket temp gage... good idea but, I'm a purest... I want to have the original.

=R

Well, you wouldn't have to change over to the aftermarket gauge permanently. Just hook it up to make sure your original gauge is reading accurately. Then you would know if you have a overheating problem or a bad temp gauge. I'd just sit the gauge on the fender and hook it up to the outlet on the engine. Let vehicle get up to operating temp in the driveway and see if it reads 212.

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I bought a new aftermarket temp gauge at a swap meet one time....guy had a bunch of them....I think the cost was $5. It had a light in it...seems like it was 6v. Anyway, I used it for a few years and it worked fine. Finally figured out how to use the 1941 new gauge by swapping faces.....now all is back to original. You certainly don't have to pull the entire cluster just to remove the temp gauge. They all have 2 small screws holding them in, and you just have to gently finagle them out of the hole.....maybe by tilting and/or turning them a bit. Kind of a pain, but do-able.

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Hiya Robert. Let us know what the mechanic says. I think if you can put your hand on the motor and on the rad tank it's not really at 200 degrees. Especially if you can do that at the rear of the head where the sender is located. You can get a little instant reading meat thermometer for about $10.00 that will give a pretty good reading off the block or the coolant. They read up to 220 degrees.

For you guys that forgot Rob, this looks something like his car. The mechanic is pointing to the sender area.

post-64-13585345511159_thumb.jpg

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Robert,

Good to see you back on the Forum.

Looks like some good advice above, but I just thought I'd give an opinion...

Your problem sounds very much like a radiator issue, to me.

If the temperature gauge capillary or bulb was broken, the gauge would not work at all.

I had a problem with my coupe, some time ago.

Would run fine all day if kept below 60mph. Go to 61 and it would start to boil, very quickly.

Turned out that the radiator was partly blocked with sludge and, over 60mph, the faster water flow through the parts of the radiator that were working would not allow enough cooling before the water flowed back to the engine.

Bryan bought the car, re-cored the rad straight away and has never had a problem since.

Good luck with the fix.

Let us know how you get on.

Robin.

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Hiya Robert. Let us know what the mechanic says. I think if you can put your hand on the motor and on the rad tank it's not really at 200 degrees. Especially if you can do that at the rear of the head where the sender is located. You can get a little instant reading meat thermometer for about $10.00 that will give a pretty good reading off the block or the coolant. They read up to 220 degrees.

For you guys that forgot Rob, this looks something like his car. The mechanic is pointing to the sender area.

Sure enough..and I appreciate the fact that she has removed her dress so as to prevent getting it soiled as she works on her car...

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  • 2 weeks later...

Hey guys! Well, the problem is solved for the time being... after having the car at my buddies garage one afternoon, we let it run... the temp gage red 200 and went up to 210-212... Dale put his hand on the rad, cool as a cucumber! And, we tested the temp in the rad... 140! Then, we felt the temp at the rear of the motor... it was warm! We figured out that there must be some blockage towards that part of the motor... he took the thermo out, and now the car runs nice and cool! On short trips, she stays around 160 to 170... and on long trips during the day, she stays under 200. By the winter time, we'll put the thermo back in to see how it does... we're hoping that the extra water flow will help unblock whatever little blockage there is.

She's driving nice, sounding nice, starting nice and everything seems to be going rather well for now... I know I wanted to have more water flow since it's getting warm now... works for me!

Thanks guys for all your imput and help!

=R

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Robert , You can check that thermostat real easy . Just put it in a pan of water and bring it to a boil , watch to see if the thermostat opens as it should . Put your thermometer in the pan too . The thermostat helps to bring your engine up to operating temperature quickly and then it should open .

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Robert, another sorta long shot is something touching the temp sender tube, that is pretty hot, such as an overheated electrical wire. Trace the path of the sender tube, the one with the coil spring around it, through the engine compartment and make sure it's not rubbing on a wire, oil line, and such.

BTW, your mechanic, would she have time to point out a problem I'm having with my fuel tank?

:cool:

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Robert, another sorta long shot is something touching the temp sender tube, that is pretty hot, such as an overheated electrical wire. Trace the path of the sender tube, the one with the coil spring around it, through the engine compartment and make sure it's not rubbing on a wire, oil line, and such.

I doubt that heating the capillary would make any difference on the gauge reading. They work by always having some fluid in the bulb. As it gets hotter the fluid evaporates which raises the pressure in the system (including the capillary). The higher pressure raises the boiling point of the fluid. So some/most ether remains in the liquid state.

There is very nearly all the ether is in the bulb so it is the temperature of the bulb that is the dominate contribution to the pressure that the gauge head reads.

Robert: Pulling the thermostat is, at best, a band-aid. And you really don't want all the crap that is in the engine getting in to and clogging the radiator. That can lead to an expensive radiator core replacement. Better to pull the core plugs and mechanically clean out the cooling passages. You probably ought to also pull the water pump and distribution tube and see if the tube is clogged or rotted away.

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Gotta agree with Tod on this. It depends on what the car is doing under real conditions. Rob's car (Jenny) is his daily local ride with some longer freeway runs. Having ridden in Jenny, I'll say she seems pretty capable. If she's overheating it will become real obvious as summer comes on and coolant spews. Then it't time for Rob to call Norm's Speed Shop. :)

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waterdis.jpg[/img]Hi all, here is the crap that comes out of the water dist tube, this one was brass and ingood shape so she went back in after cleaning, I pulled 3 freeze plugs and rod those areas out, I then ran a pressure washer through the block for several minutes till evrything ran clean water.i know it's not all out, but a lot is, if I open the petcock valve clean antifreeze runs out, the antifreeze in the rad always runs clean.............This a must for an old flathead...Fred ;)
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Rob,

You might just want to try a simple back flush of the cooling system. Don't have to take anything apart other than to install the back flush tee in the heater hose. Won't cure a badly clogged system but it might help.

Jim Yergin

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Hi all, tonight I pulled the cheap aftermarket gauge sending unit out of the head. I then filled a container of hot water from my water cooler. The sending unit measured this water as 180 degrees, the oven thermometer measured the same water at the same time as 160. So there is 20 degrees difference. This gauge was showing the thermostat opening as 180, when the thermostat is a brand new 160. I did test my meat thermometer with the hot water from our new hot water tank, it is factory set at 140 degrees, my thermometer measured 140 dead on. So which is the accurate gauge. I refilled the engine with the coolant, by the way the coolant that ran out of the sending unit hole was pretty clean, just a few crumbs inside, I probed around inside no big crud build up. Started the engine, she warmed up to 180, then the thermostat opened, it went down to 170 or so, then settled at 175, I then took the temp of the rad it was 155, I could touch the rad, the engine by a quick feel was not a lot hotter, and there is no way it was running around 180. The outside air temp was 55. I hope I have solved my problem, I will verify the oven thermometer to make sure it was accurate.......Fred

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