Water temperature gauge fluctuation (87' 2.9L)

[Keith333]

Hi everyone. My name is Keith and this is my first or second post here. I've been driving my 1987 Ford Ranger (2.9L, 5-speed with AC) for over ten years now. The only reason I mention the length of time is that in all that time, the temperature gauge, once the engine was warmed up, would pretty much lock-in at a constant location between the "R" and "M" (what I've always assumed was manufacturers "normal") barring any abnormal driving and/or heat conditions. I've had to replace the heater core and radiator lately, both due to leaks. The core was an easy thing to diagnose and fix, so not an issue. The radiator developed a small leak (on top near the hose connection, so it was easy to see) and I tried some radiator stop leak in hopes of saving or at least postponing investing in a new radiator. The hole seemed to just get bigger and it eventually overheated on me one day and I replaced it promptly then. I also replaced the t'stat as a precaution thinking that may have contributed to the overheat situation. Hoses are good, so short of replacing the pump, fan clutch and temp sensor (and anything else I've failed to mention), I should have a good-as-new cooling system. I also flushed and back-flushed it a couple of times before and during the repair cycles.

Here's my current problem though: Now my temperature gauge fluctuates between normal and close to H (Hot), but not quite there. For anyone not familiar with the temperature gauge on an 87', it begins at the bottom Cold (C) and peaks out at the top Hot (H), with a wide "normal" operating range between spelled out with the letters NORMAL. Where before all these changes my gauge would pretty much lock in between the "R" and "M" (midway) on the gauge, it's now fluctuating between that and sometimes peeking out at the top of the "O" (close to hot, but still within normal) before returning back to normal. I've been racking my brain lately trying to figure this out - it seems the t'stat is fine and the cooling system is actually "cooling", I've just never seen the gauge fluctuate like this before. While these temps are still within manufacturers "normal", I'm concerned that something else is wrong with the cooling system and I keep a real close eye on the gauge anticipating another overheating problem.

Any thoughts, insights or suggestions would be greatly appreciated. Thanks in advance!

 

[IMenriched]

Hi everyone. My name is Keith and this is my first or second post here. I've been driving my 1987 Ford Ranger (2.9L, 5-speed with AC) for over ten years now. The only reason I mention the length of time is that in all that time, the temperature gauge, once the engine was warmed up, would pretty much lock-in at a constant location between the "R" and "M" (what I've always assumed was manufacturers "normal") barring any abnormal driving and/or heat conditions. I've had to replace the heater core and radiator lately, both due to leaks. The core was an easy thing to diagnose and fix, so not an issue. The radiator developed a small leak (on top near the hose connection, so it was easy to see) and I tried some radiator stop leak in hopes of saving or at least postponing investing in a new radiator. The hole seemed to just get bigger and it eventually overheated on me one day and I replaced it promptly then. I also replaced the t'stat as a precaution thinking that may have contributed to the overheat situation. Hoses are good, so short of replacing the pump, fan clutch and temp sensor (and anything else I've failed to mention), I should have a good-as-new cooling system. I also flushed and back-flushed it a couple of times before and during the repair cycles.

Here's my current problem though: Now my temperature gauge fluctuates between normal and close to H (Hot), but not quite there. For anyone not familiar with the temperature gauge on an 87', it begins at the bottom Cold (C) and peaks out at the top Hot (H), with a wide "normal" operating range between spelled out with the letters NORMAL. Where before all these changes my gauge would pretty much lock in between the "R" and "M" (midway) on the gauge, it's now fluctuating between that and sometimes peeking out at the top of the "O" (close to hot, but still within normal) before returning back to normal. I've been racking my brain lately trying to figure this out - it seems the t'stat is fine and the cooling system is actually "cooling", I've just never seen the gauge fluctuate like this before. While these temps are still within manufacturers "normal", I'm concerned that something else is wrong with the cooling system and I keep a real close eye on the gauge anticipating another overheating problem.

Any thoughts, insights or suggestions would be greatly appreciated. Thanks in advance!

You may just have a sticky T-stat ...or it could be just a failing temp sending unit for the gauge, both of which can happen easily. personally I don't trust the factory gauges, and suggest that you get a nice set of mechanical gauges.

When you installed the new radiator and heater core....did you thoroughly flush the block of the can of goop of stop leak?....if not, that stuff can sometimes cause more problems then they fix.

 

[Keith333]

Thanks for the reply IMenRiched, I appreciate it. I'll try a new sending unit. I priced one at AutoZone for $6.99. Also may try another new t-stat as well, but I want to try a good chemical flush first and see what that does. I did the chemical flush prior to noticing the old radiator leaking (it was pretty gunked up before that and wouldn't even drain through the drain plug, the flush cleared that up though), and I do recall backflushing the system before pulling the old radiator (and after trying the stop leak), but not a chemical flush. I've seen comments about the "stop leak" stuff similar to yours at various forms, so another good chemical flush sounds like a good idea.

The system seams to be good and tight, complete with a new cap with a free flowing overflow tube and tank, but one thing I noticed this afternoon is that a had a small drip leak in the new heater hose near where I had installed the backflush adaptor. I first thought it just needed a simple clamp tightening, but on closer inspection it looks like I may have accidentally cut it with the blade when I was cutting the new hose to length - like I changed my mind on the length but didn't realize I had already made a small cut. The cut was on the bottom and when I lift the hose up, it in effect "opens the wound" and sprays out instead of drips. Hopefully this will explain why I've been losing a little water each day.

Packed full of water, the fluctuation was minimal this afternoon (maybe midway to "R" and back). I'm now thinking that maybe it gets progressively worse as it bleeds off water through the pressurized cut hose (?), but I've never had to replace more than maybe a cup of water to top it off.

I've had similar thoughts about getting a mechanical gauge too. I haven't purchased or installed a mechanical gauge in years, so any recommendations?

Also, on the temp sensor, it looks like its the single wire unit and the Haynes manual specifies the sealer to use. I've read somewhere else that it needs a special sealer because the unit grounds itself to the block (?). I've read that on the two wire units you can use a standard plumbers tape, but not the single wire units. Any helpful thoughts on that?

Thanks again, I appreciate your help and insight.

 

[Keith333]

UPDATE: Drove it to the parts store (appr. 10 miles) and fluctuation was minimal, but on the return trip it increased. I replaced the damaged heater hose, warmed it back up, burped it and toped it off. Took it for a long drive around the block and temp never went above factory normal (what I was accustomed to seeing prior to all the repairs earlier). It did fluctuate just a tick to the cold side though, but it was slower roads and it was about 30 degrees here in Middle Tennessee. Still plan a chemical flush and sensor replacement.......