My stock water temp gauge died, however, I do have a autometer oil temp gauge hooked up to the oil pedestal. Is there any reason to fix/replace the water temp, shouldn't I be able to note a overheating situation with my oil temp gauge?

 

i wouldn't rely on it...

 

Water will overheat and show sooner on the coolant temp gauge than the oil temp will. Since the oil has it's own cooling/heat rejection system, it is not directly tied to the water temp. While you will/may notice a rise in the oil temp, by then it may be too late for the engine.

Coolant temp is too critical not to have a working gauge reading for.

 

How would you hook up an aftermarket coolant gauge?

 

The question has been asked/answered soooo many times. To make it simple, there is a land on the back of the water pump housing near the #2 coolant temp sensor. This is the best spot to drill and tap for the sensor.

 

I beg to differ Trochoid, here is a better way:







And here's the post that led to this new way of doing things, with details on how to do it:

https://www.rx7club.com/1st-generation-specific-1979-1985-18/second-water-temp-sender-tip-installation-question-631760/

 

Ray, I know we have differing opinions on this, but if the thermostat ever sticks closed in your method, the engine is toast before it registers on the gauge.

 

+1 trochoid i have had a engine over heat with the rad cap off and my finger in the rad my dumb *** mistake luckly enough it did not hirt the engine got 30,000 on the rebuild.
eric

 

"if the thermostat ever sticks closed in your method, the engine is toast before it registers on the gauge"

That's certainly an important point Trochoid and in my case not a real problem, since my stock electrical gauge still works, which should guard against the unlikely event of the t'stat sticking. But I bring it up for the sake of discussion and to point out that there can be more than one answer to an apparently simple question.

So, for those thinking about a second temp gauge (as I was a few months ago) here are some things to consider:

1. Is it your primary gauge? Then the water pump would be the best option.

2. Do you want a secondary gauge to "check on" your primary gauge? Then a mechanical gauge is a good idea, since it will be immune to electrical glitches. The mechanical gauge like my sunpro unit has a relatively large sensor bulb compared to the stock electrical one, would it fit in the water pump?

3. How much effort will it be? I don't have experience with converting the water pump, but adding that tap to the thermostat housing was cheap and easy.

4, and the main reason I put it in the t'stat housing, it just looks cool.

But all this does raise an interesting technical question or two.

First, if the t'stat froze shut, would there really be that big a temperature differential seen by a probe in the water pump, just before the t'stat, and the housing, just after the t'stat? After all, with the t'stat closed, the water in the water pump won't be going anywhere either and it's temp will depend on heat diffusion through the water pump casing, which is exactly how the t'stat housing would also detect a temp increase. So would there really be that big a difference in the response with the t'stat closed?

Second, if properly maintained and replaced every few years (as we 1st owners always do) what are the chances of a t'stat freezing up on you? I've never seen this happen with the 7's I've been driving for the last 7 years. For that matter, I've never had a t'stat freeze on me in my 40 years of driving.

There's always a first time, I suppose, but are we making a decision here based on a technical consideration that is essentially irrelevant?

Maybe all of this is just the ramblings of a scientist thinking in overdrive, but I don't recall these questions being answered in the earlier t'stat posts and there seems to be some relevance to the original question in this post, which was about how different temp sensors see things.

 

I believe I mentioned the danger of a thermostat sticking in your other thread. Would a sensor in the back of the wp housing show a difference between the 2 if the thermostat stuck, yes, it would. As the water pump is still circulating the coolant within the engine block.