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Erratic temperature gauge


3rdowner
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Hi all, glad to be on this site.  I am 63 yrs old and have restored cars (and everything else, tools, pianos, homes, stuff).  I am the proud new/old owner of a 1941 Buick 4-door Phaeton, 50C.  The issue: the temperature gauge bounces from hot (all the way to the right) to 2/3rd point.  It quickly resolves the high temp within 1 minute, but it makes this “trip” back and forth every two minutes.  And, for the first time (yesterday) the radiator burped steam and fluid from the cap.  I’m guessing it a malfunctioning thermostats, but before taking a wrench to the goose-neck, I think it best to ask this group what other issue I may be facing.  For some background, the car is a 98 point restoration and drives great.  It has a new radiator. Thank you in advance of any input.

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I don't know much about Buicks of that era but the typical temperature gauge of that era is a “mechanical” unit. It has a bulb filled with ether in the engine and a small capillary tube going to the dash unit. The dash unit is basically a pressure gauge, the higher the temperature in the engine the higher the pressure of vaporized ether. If your Buick has that type of temperature gauge then you can be sure that the rise and fall in temperature is really happening in the engine.

 

First place I would look would be the thermostat(s) located on the engine on the hose(s) going to the top of the radiator.

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Yes, it is a bulb system. Oddly enough, my research indicates the the thermostat is available at NAPA to this day. Makes sense, it is a simple and reliable design.  Thank you for your input, the only thing left to do is drain and fix. Q: is there a special refill procedure?  Some coolant systems require burping or priming. 

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Ply33 is correct that the original style temp gauge is a bulb filled with ether  that's at the rear of the cylinder head with a capillary tube leading to the dash gauge.  The pressure rise from the heated ether works on a bourdon tube (a coiled, flattened tube) that the needle from the gauge is attached to.  As the ether pressure rises, the coiled tube uncoils a little and the needle moves.   

 

The water jackets toward the firewall end of the straight eight engine is notorious for building up sediment, as it is far from the water pump and the circulation is weak back there.  What could be happening is that you're getting localized boiling of the coolant back there because of poor circulation, and when the bulb for the gauge ends up in a "bubble" of vapor rather than liquid, it reads cooler (vapor does not conduct heat as well as liquid), and then when the bubble passes and the bulb gets back into liquid the gauge temperature goes back up.

 

The only cure, and I had to do this, is to remove the head and to dig out the mud that you will find back there with long screwdrivers, coat hangers, etc. I chucked a cable from a lawnmower throttle control into a drill and inserted it into the water jackets and roto-rooted it!   My engine's water jacket was more that 1/2 blocked back by #8 cylinder.  

 

If you remove the head to do this, be VERY CAREFUL about removing the bulb for the temp gauge from the head.   I ended up twisting the capillary tube off the bulb and had to replace the whole thing.   The bulb slips into the head and is held in place with what I would describe as a compression nut that fits around the bulb and screws into the threads in the head.  I recommend soaking that sucker with a penetrant for several days before attempting to unscrew it.  I'd also turn it only a tiny bit at a time, checking that the bulb and capillary are not spinning along with the nut.  The bulb and capillary must stay still and only the nut can spin.  Maybe turn the nut back and forth like 1 degree of motion to try to break any rust that's gluing the nut to the bulb while spraying on more penetrant.

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The last rocker arm stanchion  "bolt" on the distributor side of the engine is actually a stud. The stud hole is tapped through to the water jacket directly above the temp sensor bulb. If you remove the stud you have access to the water side of the bulb and you can manipulate the bulb through the hole to loosen it.

It still can be a challenge.

Be sure to use a sealant when replacing the stud or you will get water in the oil.

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27 minutes ago, DFeeney said:

I would remove the capilary tube from the block and put it in a can of very hot water to see if it acts the same before I would take any thing else apart.

I wouldn’t. That capillary tube is pretty fragile and if it is working at all, which it apparently is, then it is very likely to be reading correctly.

 

The suggestion by @DonMicheletti is simply and can’t hurt. The next easiest is to pull and check the thermostat. After than I would follow @Pete O and try to get the block and head cleaned out. Pulling that sensing bulb and the capillary tube is the last thing I would do (been there, broken that).

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4 hours ago, DonMicheletti said:

The last rocker arm stanchion  "bolt" on the distributor side of the engine is actually a stud. The stud hole is tapped through to the water jacket directly above the temp sensor bulb. If you remove the stud you have access to the water side of the bulb and you can manipulate the bulb through the hole to loosen it.

It still can be a challenge.

Be sure to use a sealant when replacing the stud or you will get water in the oil.

 

 To go a little further,  I have seen longer studs or bolts used in that position, pinching the bulb.  As Don said, a challenge. Be careful.

 

  Ben

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2 hours ago, DonMicheletti said:

To me, the wild gage oscillation says gage problem. An engine couldnt change temperature that quickly - unless,maybe, the water is low.

 

It is not an electrical device what might have some partial short to ground causing rapid swings. It’s a pressure gauge measuring the vapor pressure of the ether in the bulb. If the needle is moving that quickly that means the pressure is changing that quickly and that means ether in the bulb in the head is heating and cooling that quickly. No other way around.

 

Per @Pete O it could mean that the bulb is sometimes in hot water and sometimes in steam because the back of the block/head is filled with crud.

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Thanks all, I put a new thermostats in yesterday, it was such an easy thing to do I figured I would eliminate it from the Fault Tree.  Haven’t had a chance to run it yet, but will report back with a day after doing so.  I was surprised at the thick rust residue on the old thermostat, I think a serious flush is in the near (this weekend) future.  I am open to the best concoction for the job.  Back in the day, my father may have suggested a diluted TSP or something in the Rust-Away family.  I want to be careful not to hurt the sealed bearing in the water pump. Ideas?

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Update:  I could not wait to test the cooling system, so I took the car for an hour drive at speeds of up to 70 MPH.  The temperature gauge stayed-put at the midpoint without fluctuation.  This is good, but I am confident that the collective experience of this forum know not to get excited on an “n” of 1.  I will keep all updated.  My next post should include I.R. readings of the block, front-to-back so as to eliminate the “cylinder #8” issues brought-up on this post.  However, as a retired engineer (as of last month) and having founded and ran an engineering firm in the R&D and Manufacturing of organ transporters and other thermal-dependent devices, I must agree with ply33, the temp gauge moves with pressure/temperature changes (PV=NrT), and the change in pressure is due to an increase in temperature.  Also, with a “stuck” thermostat, the potential for the coolant to “flash” to steam at the #8 cylinder and being the furthest from the point of cooling point (radiator) it is obvious why the boys and girls at GMI (the validation point for Buick in the 1930’s/1940’s), placed the sensor at the hottest point on the cooling jacket.

With all that said, it is still a data point of 1, and as we have all witnessed in the news over the past year, liars figure and figures lie (a mis-quote of Mark Twains “Figures don’t lie, but liars figure”).

Thanks again all, I hope to help others with issues in return.

 

PS: Gas gauge is the next thing to fix, but it has been isolated to the send-unit.  I have never enjoyed removing gas tanks, it’s a job best done on a lift.  And for some background, my diagnosis found the gas gauge reads “FULL” with the send wire disconnected and “1/8” when grounded, the same state it reads when connected and ignition on.

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35 minutes ago, 3rdowner said:

. . .  However, as a retired engineer (as of last month) and having founded and ran an engineering firm in the R&D and Manufacturing of organ transporters and other thermal-dependent devices, I must agree with ply33, the temp gauge moves with pressure/temperature changes (PV=NrT), and the change in pressure is due to an increase in temperature. . .

Welcome to the retired engineers club. I’ve been in it for about 8 years now.

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I wish you hadn't run the car without installing a filter in the cooling system before the radiator.  Especially after long disuse, the block will disgorge flakes of rust loosened by the action of the water pump and will promptly deposit them in the radiator.  I use women's calf-high stockings as worn with slacks--I think I paid $7 at Walgreens for a box of 20.  Drain off enough coolant and remove top radiator hose.  Use a blunt handle of a screwdriver or ratchet to push the toe of the stocking well into the top tank of the radiator.  Fold the open end over the outside of the radiator neck, and re-install the upper radiator hose so that all coolant passes through the stocking while entering the radiator.  Drive 100 miles (not much more the first time), drain a sufficient amount of coolant (which you can re-use), remove the stocking and see how much debris has been captured.  The quantity will inform you as to what the next inspection interval should be.  Rinse out the stocking and re-install.

 

The reason for the limited number of miles before checking is so that you do not capture so much debris that the now-full toe is too large to easily come out through the upper neck.  I learned that the hard way with my Paige, and spent an hour massaging the debris-filled toe with chopsticks (yes!) to make it slender enough--but longer--to get through the upper neck.

 

The stocking works far better for me than a Gano filter designed for the same purpose, as it captures very small pieces of debris--as well as the "sludge" from previous owner's overuse of soluble oil.

 

Whenever you have used a chemical flushing compound, discard *that* stocking and install a new one after the water flush before adding new coolant.  After 1,000-2,000 miles of this process, the stocking cleaning exercises can be done only every 3 or 4 years.

 

Further, when a block has been boiled out as part of a rebuild, there's a gray coating that seems impervious, but after 20 or 30 heating-cooling cycles the coating loosens and flakes off.  So the stocking technique should be used on rebuilt engines as well.

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Hi Grimy, thanks for the suggestion, I will filter my next project.  However, I my have misrepresented the condition of this car.  I bought the car from Mike Stowe, owner of Great Lakes Motors, a well know restorer and collector of “mostly” American cars.  The car has been completely restored, frame-up.  The radiator, hoses et. al., are new.  Mike drove it once a week to breakfast within our small town (Boyne City).  The rust color I spoke of was on the thermostat, but it was not caked-on, just discolored.  I will drain the system this weekend, simply for investigative reasons, no issue at this point.  As for the stocking, I do have some stainless steal mesh ranging from 10 um to 80 um I use a pre-filter on a well-pump for our home (off the grid).  You have encouraged me to make a filter between the goose neck and the radiator.  It will be removable, but it is so easy to switch-out the return radiator hose that it makes total sense.  I did check the fluid color today, bright green no signs of contamination.  Last, and not at all least, the IR temp gun (using emissivity) indicated balanced temp across the entire block.  I did not write it down, but 150 F was the basic mean with little more than 2 degrees delta.  When I figure out how to post pictures, I will do so!

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Closing the loop:  Thanks all for the keen insight on all potential issues for my erratic temp gauge on my 41 Buick 50C.  I changed the thermostat, replacing it with a 160 F unit, and the needle is rock solid in thre middle.  I ran a quick test on the old thermostat as per the attached pictures.  The pictures came from a video, but the video is too large to post.  Bottom line: the thermostat was closed at 180 F, began to “cracked” at 200 F and was open at 208 F (all approximates, but my cooking thermometer is within 2 degrees F at 200 by eye when compared to a calibrated lab Mercury thermometer).   So, basically the old thermostat is toast.

 

Last, and referencing Grimy’s in put (thank you), I flushed the block (actually pretty clean) and the heater core (not clean at all).

 

PS:  I think I made a mistake (correctable) with respect to gasoline over the weekend.  I put non-ethanol gas in (good) but it was 94 octane (bad). My engine runs a bit rough, sounds like a slight miss.  Could this be due to the octane?

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