1995 mustang runs hot

Hey All,
Need some advice again. I have a 1995 mustang gt, 5.0L, ~90k miles
that, all of a sudden, runs hot according to the in dash temp gauge.
4 years ago I replaced the ECT and all hoses, belts, coolant and
thermostat (180 degree unit). Never had a problem with overheating
and it never got to the right of the 12 o=92clock position on the
gauge. After not running it for a couple months, I drove it in
ambient 75 degree weather and the gauge was on the =93L=94 of =93NORMAL=94.
It wasn=92t in the red but maybe a needles width or two below. It
climbs to the =93L=94, the fans kick on and then it drops down to the
=93A=94. I just replaced the temp sender to the gauge and have the same
problem. According to Haynes, the sender should read 97 ohms cold and
drop as the engine warms up. Mine read 330 so I replaced it.
Replacement read 280 ohms cold so I got yet another one that also
reads about 300 ohms cold. Is the book wrong or do I really have 3
bad sensors?
I have started it cold and held my hand on the upper radiator hose
until it got hot which was at the =93M=94 of =93NORMAL.=94 That hose used =
to
get hot at the =93O=94 and then fans came on between =93R=94 and =93M=94. =
I
suspect it=92s the gauge itself but don=92t know how to check it. I went
to my FLAPS and they had a mechanical temp gauge that went in the
radiator but it was $150+. What should my next step be here?
TIA,
Derek
Reply to
genius
most likely the haynes manual is wrong.
You could use one of those infrared temp measuring things.
Might want to check the thermostat. Maybe it went bad despite the low age.
If the fan isn't coming on at the correct temp then check the fan's temp sensor. I don't know about the '95 5.0L, but my '97 4.6 has two temp sensors. One for the gauge the other for the fan.
Reply to
Brent
Thanks for the reply. I thought about one of those infrared temp things but where do I point it, thermostat housing? How accurate are they? If they are within 20 or 25 degrees I would think that would help. Yes, the 5.0L also has 2 temp sensors, the ECT for the PCM and the sender for the gauge. Both replaced. If it was the thermostat, wouldn't the fans come on before the thermostat opened? If that happened I would have caught that when holding the upper hose.
Reply to
genius
The cheapies are accurate to within a couple degrees. WAY less expensive and more accurate than the old optical pyrometers.
One thing you can do is check various places along the radiator... the incoming water should be hotter than the outgoing water, and there should not be any cold spots in the radiator. If you see cold spots, it is because some sections of the radiator are clogged.
The cooling system will work fine if the coolant is circulating properly. A clog in the radiator, a bad thermostat, a bad water pump, or a clogged block can keep the coolant from circulating properly. --scott
Reply to
Scott Dorsey
water pump vanes corrode, 1995 is probably due for replacement.
if not electric fan => the Fan Clutch could have gone bad.
Does it overheat with AC on or off ?
The radiator cap may have lost its pressure holding capability, replace.
Watch the water level closely and see if you losing steam or water over time, if not gauge is off.
if you have a code reader, you could get the "water temp" as put to the computer.
many after market thermostats are not that good.
Good luck and let us know what you find out
-1993 5.0 8# KB
Reply to
Chumley
Thanks for the response. I replaced the radiator cap with a new 16lb Stant. No coolant loss, no water in oil or oil in water. Doesn't get any hotter or stay any cooler with ac on vs off. Car has electric fan, it does cycle on and when idling, maybe 20-30 seconds later, shuts down for 1-2 minutes, then repeats. I got the car hot, turned it off and pressed my hand (where I could get it, wedged between fan blades, belts and pulleys) against the radiator and it seemed to be hot everywhere I touched. Crawled under the car and grabbed lower radiator hose. It wasn't nearly as hot as the top radiator hose but still warm to the touch. I got a stant superstat from Napa as I thought they were supposed to be the best and coolant is nice and green, no floaties and good to -30f according to my cheapie hydrometer. I really suspect the gauge or sending unit but am not sure how to test accurately. I will try to get an infrared temperature reader as soon as I can.
thanks for the tips!
Reply to
genius
Are you you sure you are looking at the right sending unit for the temp gauge. This may have one sensor for the computer and fan operation and another that is for the temperature gauge.
-jim
Reply to
jim
How accurate are they? If they are within 20 or 25 degrees I would think that would help. Yes, the 5.0L also has 2 temp sensors, the ECT for the PCM and the sender for the gauge. Both replaced. If it was the thermostat, wouldn't the fans come on before the thermostat opened? If that happened I would have caught that when holding the upper hose.
They are not super accurate... You aim them at the area you want to measure. If you get an answer within 20F, I think that is about normal.
Reply to
hls
Scott, I have tested these under laboratory conditions, versus mercury thermometers, and I have not found them to be so very accurate.. Our laser units are cheap, in the $100 range. Good enough for some types of measurements but not really good enough for what I do.
Maybe within 20-25F. Maybe...
I normally work in the range of 160C, or that equivalent in F.
Reply to
hls
Thanks for the response. I replaced the radiator cap with a new 16lb Stant. No coolant loss, no water in oil or oil in water. Doesn't get any hotter or stay any cooler with ac on vs off. Car has electric fan, it does cycle on and when idling, maybe 20-30 seconds later, shuts down for 1-2 minutes, then repeats. I got the car hot, turned it off and pressed my hand (where I could get it, wedged between fan blades, belts and pulleys) against the radiator and it seemed to be hot everywhere I touched. Crawled under the car and grabbed lower radiator hose. It wasn't nearly as hot as the top radiator hose but still warm to the touch. I got a stant superstat from Napa as I thought they were supposed to be the best and coolant is nice and green, no floaties and good to -30f according to my cheapie hydrometer. I really suspect the gauge or sending unit but am not sure how to test accurately. I will try to get an infrared temperature reader as soon as I can.
thanks for the tips!
Actually plain water cools the best, but in the long term causes corrosion problems, the green stuff is less conductive, much less corrosive, but does not have the cooling capacity of plain water.
The thermostat should have a small hole, or small hole with small rivet in the top half to allow steam and help open the thermostat on Mustang, well the 93, other cars don't have it.
Fan sounds like it is doing OK, and cycling indicates it is cycling through the temperature range, and it is sitting on the high side.
you still could have worn water pump, not sure how to check it. I replaced mine suspecting it might be a problem when my car was running hot, and it was corroded quite a lot, missing a lot of impeller blades, probably only had 1/2 the amount of flow, that was at about 115k miles. I put in a performance part. With a supercharger, you have to pull out all the stops to get the best cooling.
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if you can afford it, should work on a 95, tells you what the computer is seeing, so if the water temp is 200 or so, then it is fine. The thermostat change to 180 will not lower the water temp to 180, the engine will still produce a lot of heat. Thermostat has two temperatures one for opening and one for closing and cycles between, the one you have has less with the notch in it which seems fine. Stock thermostat then water => about 220 180 => about 200 160 => about 185 or so (approximate)
Reply to
Chumley
I have seen them to be better than that... but they _do_ measure surface temperatures, so if you put a mercury thermometer into a steak and then point an IR pyrometer at it, you should expect a sizeable difference.
I was mostly interested in the things for measuring transmitting tube plate temperatures, and I found several of them all to agree with one another very accurately. This doesn't necessarily mean they all match a standard reference but it's a good sign... and they did measure boiling water within a few degrees. --scott
Reply to
Scott Dorsey
I haven't read all the posts on this thread and I don't know if this applies or not but ... Back in January I gave my 1995 Ford E150 van to my son. I had purchased the van new and put 92K miles on it with no problems except for normal repairs (brakes, tires, etc). My son recently took his family on a trip to Atlanta and the Gulf Coast and, wouldn't you know, he had overheating problems. The leaking water pump was replaced, new thermostat, and fan, and the van still overheated. Finally, the radiator was replaced, and no problems since then. Is it possible that your 1995 Mustang just needs a new radiator?
FWIW Dick in MN
Reply to
dickr2
Good point...That is always a possibility. Some years ago it was cheap and effective to take the radiator to a shop and have it rodded and chemically cleaned.
Now, some of the alloys used and the construction methods may not lend themselves to this old technology.
Really, cooling problems are usually pretty simple. There are a finite number of things that can be happening.
And, to fix them, you have to work systematically through the system. As in many other cases, to throw parts at this problem can be very expensive. A little diagnosis can go a long way.
Reply to
hls
How to test that one ? my 93 is making that sound a bit now, (had a broken one in a 89, rattled but had a loud resonance)
Reply to
Chumley
Update:
I took the car to a friend of mine that has an OBD1 scanner. From what we could tell, the ECM saw the thermostat open at roughly 182 degrees. The fans kicked on at 210 degrees and off around 200. From what we saw, everything looks fine under the hood. It looks like the in dash gauge is the culprit which I was fearing. The parts are extremely hard to find and expensive as can be, ~$400 via dealer which is the only place I can even find the part.
Does anyone have any other options other than these for monitoring the temp? 1. Ignore the gauge indefinitely (not my preferred solution) 2. Get some sort of aftermarket gauge cluster 3. Purchase my own OBD1 Scanner, keep it plugged in, tape to dash.
Thanks again.
Reply to
genius
Update:
I took the car to a friend of mine that has an OBD1 scanner. From what we could tell, the ECM saw the thermostat open at roughly 182 degrees. The fans kicked on at 210 degrees and off around 200. From what we saw, everything looks fine under the hood. It looks like the in dash gauge is the culprit which I was fearing. The parts are extremely hard to find and expensive as can be, ~$400 via dealer which is the only place I can even find the part.
Does anyone have any other options other than these for monitoring the temp? 1. Ignore the gauge indefinitely (not my preferred solution) 2. Get some sort of aftermarket gauge cluster 3. Purchase my own OBD1 Scanner, keep it plugged in, tape to dash.
Thanks again.
*****
Do you have a good wrecking yard nearby? You might try that.
Second to that, I would probably get a single unit temperature gauge and install it as professionally and inconspicuously as possible. You can get aftermarket gauges for some cars that will fit right in the dash. I have seen this done, but have never done it myself.
I would be hard pressed to give a dealer $400 for something like this, but I wont say it would never happen.
Reply to
hls
Yes it sounded like the coolant temp sensor and fans were working as they should. The gauge is just reading higher than it used to.
Probably the gauge is reading high because a resister that shunts some of the current to ground is burned out or has a bad electrical; connection. The purpose of the shunt resister (in combination with a capacitor) is to smooth out the reading (keep the needle more steady).
you could replace the resister. It doesn't have to be under the dash. The resistor can go from the sending unit output to ground anywhere between the sender and gauge. If you get the right resistor it should be as accurate as it was. A wild guess would be the resistor needs to be around 200-1k Ohms.
The other option is to just leave it as it is. You now know what the needle reading it is now giving mean.
-jim
Reply to
jim
I called the local wrecking yards and didn't have any luck. One of them told me that gauge was only in the 95 mustang GT convertible and that regular mustangs and cobras would not fit. Not sure how accurate that is but if that is the case, finding a working unit in a bone yard will be difficult at best. Agreed with $400 for an "indicator" but even if I know the car is running fine, driving around with the gauge in the red will still be disturbing.
Reply to
genius

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