would a coolant pressure gauge be useful? Update: YES!

[BLINGMW]

Just thinking. Give me your thoughts:

My temp gauge likes to crap out on me every now and then. I was going to hook up another temp gauge as a backup. But instead, what if I hooked up coolant pressure? My thinking is that it might be even more useful as both a suppliment and a backup.

If I had a leak, and was losing coolant, I would see it long before the temp gauge would. That'd be cool.

If the radiator cap needed replacement, I would know. Sweet.

Head gasket leaking combustion gasses into coolant? I would see it.

Now here's the one I'm not sure of. If the water pump failed or the belt snapped. Would the pressure stay constant because it's regulated by the cap even as the coolant got hot? Or would pressure rise faster than the cap could bleed off and I would see it before the head gasket asplode? That'd be neat if so, and like I said, maybe even more useful than a temp gauge.

:?:

[Maengelito]

since the cap regulates the pressure, i dont think a coolant pressure gauge would do much except tell you the rating of the cap. also, if you had a leak, a coolant pressure gauge wouldnt tell you if it was in a line or the headgasket or where. it'd just show that the pressure was down. obviously, its not gonna hurt to monitor the status of coolant, but i dont think it would be of much value

[BLINGMW]

yeah, that's the big question for me, is the system going to overpressurize quickly enough to overcome the cap and register as a spike if things are getting too hot? Dunno. And sure, reading low doesn't tell me exactly what the problem is, but it might be a good indicator to get off track.

Any other thoughts? If it's a total waste of time, I'm not going to bother. Otherwise, I'm hooking it up at lunch tomorrow I can let my car idle and get a little hot (by not turning on the fan) and test the theory a little bit.

[Jeff]

I dunno. Seems rather random. A good accurate (autometer!!) temp gauge would make more sense to me.

[BLINGMW]

I dunno. Seems rather random. A good accurate (autometer!!) temp gauge would make more sense to me.

maybe it is. I'm just curious. If the temp gauge keeps giving me trouble, I will replace it, but I just thought this might tell me more. We'll see!

[Jeff]

What happens with the gauge? Just wondering what your problem was. As a TD owner I have lots of experience with randome cooling system issues...(shut up nick...)

[Nick325is]

Have you checked the ground on the instrument panel as well as under the dash. My coolant temp gauge fluctuates alot and I believe this is the cause of it.


Nick

[BLINGMW]

What happens with the gauge?

it works perfectly 98% of the time. Accurate as verified by my infrared pyrometer and tire temp pyrometer. Now and then it'll just jump all the way to 0. Sometimes for a day or two, sometimes just up and back a few times and then fine again for weeks. By cleaning the grounding nut on the back and tightening it, it got a lot better. And I might do that and check other grounds again if I get bored and it gets worse.

[Jeff]

Check the ground at the sensor!!!

[BLINGMW]

sweet!

I hooked up a gauge to read coolant pressure today. I think it's the new hot thing, you ain't cool if you don't got one.

I will play with it some more, but I think it's pretty useful, (at least for me) maybe even more so than a temp gauge. When cruzing or idleing, at normal operating temp (175 for my car with its slightly lower than stock thermostat), it reads about 7 psi. But if I let it sit and idle, and don't turn on my radiator fan, just letting the coolant temp raise to 180 brings the pressure to 10. 185 is more like 13.

My GUESS is that if the temp were to go up to the 190's, the cap would start to vent, and the gauge would level off at 17 psi as that's what my cap is rated. I might test that theory later. But since my normal operating temp is lower than that, if my gauge was ever showing 17psi, I'd know something was not quite right. HOW not right, I may not know, but it's time to shut it down!

So for the most part, during normal operation, the pressure gauge pretty much follows the temp gauge.

But it seems a little more useful, because it's going to react imediatly to a sudden leak. And if there's a slow leak, or the cap isn't sealing quite right, when I shut down the car, the gauge is going to drop much faster than usual. Right now, even an hour and a half after shutting off my car, it's still at 3 psi. Remove the cap and it drops instantly.

Another plus to hooking one up, I don't think it would matter where you tied it in, the pressure should be the same everwhere.

The only drawback for some cars I can think of: If your operating temp and pressure are not below the pressure the cap was rated for, if they were equal, the gauge might not be very useful. If the temp was slowly climbing, the venting cap might keep the gauge showing that everything is ok. Installin a higher pressure cap or lower temp thermostat would fix that.

Also, I'm not yet sure if my operating pressure is always going to be around 7psi. Let's say it's 90 degrees outside. I start my car and the coolant is already 90 degrees at 0 psi. At 175, will my pressure gauge read lower than usual? Or if we start at 20 degrees. At 175, will I be hitting 17 psi? Thoughts? I guess we'll see.

[ScottyB]

this is really cool, keep us updated

[BLINGMW]

haha, I don't know how cool it is-- more of a curiosity? And maybe only to me and you. I can't imagine most people care! :lol:

Upon further testing today and yesterday, the gauge definatly isn't QUITE the super duper replacement for a temp gauge that I hoped it would be, but I still like it. What I was wondering about before is true.

The operating pressure IS determined by the temperature of the coolant when I start the car. Like I noted before, with ambient temps of 60-70F, once my car is up to temp, the pressure is ~7 PSI. To simulate the "hot day" situation, I let the car warm up for just a minute or two, just a little pressure had built. I opened the radiator cap, head temp was 140, water in the rad was 130, a little hotter than I meant to go, but that's ok. Now with the cap back on, and pressure at 0 again, once I went on down the road and reached normal temp (175ish), my new operating pressure was only 3 PSI. I expect that in the winter, with sub zero starting temps, I'll see normal operating pressure quite a bit higher than 7 PSI.

So that was kind of expected, oh well. The gauge will still follow the temp gauge in movement, but you can't say that 7PSI = 175F. I'll just have to note the "normal" pressure once up to temp, and if I were to lose my temp gauge, the pressure gauge can still act like a backup as long as I knew where "normal" was. So not too bad.

An interesting side note/thought. If you were at the track, and opened your cooling system to check the level or something while it was fairly warm, when you close it back up, your operating pressure is going to be lower. Which gives you less protection from overheating. :!:

Just for kicks today, when I got home I left the car idling and didn't turn on the fan. Put my temp probe on the head.... I chickened out at 225F, but as expected, the pressure gauge hit about 18 PSI sometime around 215F and didn't go any higher. At least I know it's working!

Umm.... that's all. Oh yeah, I took out my gauge cluster, cleaned and retightened the grounding nut on the back of the temp gauge. And also did this to bypass the stupid, non-functioning SI batteries. Picture and idea stolen from E30tech:



just in case any of you other few E30 people have the same problem, either one or both of these things brought back my temp gauge. Works better than ever. :wink:

[Maengelito]

FYI, i happened to be watching the busch race today. they were talkin about how dale earnhardt jr's car was loosing "water pressure" but they couldnt find any puddles when the car stopped for pit stops or any leaks under the hood. they hypothesized a pinhole leak in the radiator because it was a super speedway race so any debris they hit would hit at like 190 mph. i was thinking "chan was right with all this coolant pressure jibba jabba"