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Looking for advice on a few things maybe or maybe not related on my 51 200. I have had the car for 8 years and when operating and cruising, the temp gauge has always read at the "P" in the word Temp which is about 3/4 of the way up the gauge. Seems high to me but I have never had an overheating issue to speak of except the last trip I went on was a hot afternoon and about an hour, hour and a half drive. I felt the transmission slip/jump (almost like I let off the gas) several times after the ultramatic would shift into the higher gear. Low was fine with no issue but after the shift it would sputter/cut out a bit and eventually cruise fine again. I noticed the trans fluid level was low when I got home. I added a quart, no change, added a second quart and walked away. A week later I took it out and checked the fluid and it looked perfect, shifted fine.

Question 1: This transmission issue, do we think low fluid level was to cause, like I said, had the car 8 years and have only had that issue twice, both within my last 4-5 trips. I added two quarts of Type F.

Question 2: The temp gauge at the "P" seems high, another guy at the last show with another 51 says his runs much lower on the gauge...so do I simply have a gauge issue? Should I investigate/correct this further if I am not having any other issues? I used a temp gun when I got home while it was still running and was reading about 200-220 degrees on the top of the engine as it sat after running. Anyone know what temperature it should read or where to accurately take a reading?

Question 3: The service manual says to check the trans fluid in neutral which I thought was strange, I have always checked other vehicles in park after driving. I assume if the manual says it that is the way to do it. I'm also not sure my car has a factory dipstick for checking, it doesn't look out of place but doesn't look like the pictures in the manual either. I will post a picture for clarification that I am checking things correctly.

Appreciate the help, I've had the car for 8 years but thankfully have had to do very very little in the way of repair or even service, oil changes, lubrication, one pinion seal, that's it. It has been incredibly reliable for me. Some of these may be obvious questions but I am looking to learn, thanks all.

Picture of dipstick

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Someone has changed from the original transmission dispstick and if it is an aftermarket item any info or photos you could provide to help identify it might give some ideas to others who have been on the forum in years past. Several have asked if there is a way to modify the dipstck to avoid going under the car to check the fluid level. Seeing something that someone else has done might give them a direction. One can only hope it was done correctly by matching readings between the old and new dipsticks so the low or add fluid point is the same. Without having the factory dipstick and tube or the ability to swap one in, it will be hard to verify if the newer one is reading correctly.

You can check the fluid either in park or neutral as the valve body is in exactly the same condition in either gear position. Important thing is to keep the engine running or else if stopped, presuming a field change was done on your car to remove a valve, to make sure you are all set up to quickly do the check within one minute of the engine being stopped. With the valve removed, any longer than the minute delay and the fluid will start to drain back out of the converter and distort the reading as it runs back and fills the pan.

On the temp gauge, if the sender is old there is a chance the sender might be changing value. The 51-6 gauges need to have a resistance range of approximately 70 ohms cold and 10 ohms hot. Another poster did some checks on his 52 and came up with data indicating what the readings on the gauge are and the corresponding resistance value of the sender at specific temperatures. You will notice the resistance readings above 71 ohms are all in fairly low temperatures so the gauge will just be at the bottom of the scale until the resistance starts to get in the working range where the gauge will start to work. Fuel senders also work in the same approx 70 to 10 ohm range.

Unless you are literally shifting the lever from L to H when driving, your transmission is not going from low to high. If you are in H the whole time, you are feeling it go from converter drive to direct drive. Please clarify. 🙂

It really doesn't matter what gear you are in when checking the fluid as long as you have been out of direct drive for the given interval then shift to park or neutral when ready to check. I'm not sure why they always say neutral instead of park as the manual valve (gear shift linkage valve) is in the same position regardless. The selector shaft linkage I suppose adds like 1 oz to the reading in neutral vs. park, but who cares; the difference in reading a dipstick is surely near the limit of human perception. If you fill it properly, the extra will leave through the vent hole in time regardless.

Appreciate all the info, I will definitely try and get some more pics and measurements of the dipstick setup if it will help some out. PGH as far as the shifting, I of course just meant the converter to direct not actually shifting L to H.

According to the referenced post, regardless of the Ohms readings, the temp I was reading correlates exactly to that post..."P" on temp being about 212 degrees (assuming reading at the top of the engine or similar). So, I guess the question then is am I running a bit hotter than I should be, if all systems are functioning properly, where should the temp gauge read? Dead center?

additional info about temp gage

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