89 Daytona, poor gas mileage/no heat or showing engine temp

[daytona98]

Hey everyone, I have an 89 Daytona with a 2.5 that gets really poor mileage (10-15 MPG) and the engine temp on the dash rarely comes above the cold mark. I suspect it's a bad thermostat but am learning it maybe a coolant temp sensor as well? Before I go tearing it off I'd like to order parts, it this sensor a 2 or 3 pin on the car? Any thing else I should replace/check like o2 sensor? Thanks for looking!

[BobD]

Usually when a TD gets mileage that bad, it's almost always an O2 sensor. They rarely give an engine code. At least in my experience.
Is this a TBI car or Turbo? The 2.5 TBI's are really bad. At least mine was and have known others that never could get very good mileage. The best I could do was 22mpg (all highway) The 2.5 Turbo auto is good for about 25 mpg with normal highway driving. You're results may vary.

[Dr. Johny Dodge]

temp gauige sender is single pin above and left of the dist in the front of the head between plug #1 $ #2

the one in the side of the T stat houseing is for the computer & fan

[Jakecs]

The temp issue could be the sending unit wire or the gauge itself. Make sure it is actually plugged in at the head.

If the coolant temp sensor(CTS) is bad, the fan should stay on constantly. It could also be a thermostat stuck open like you said, especially one of those fail ones. I've had bad luck with those and wouldn't recommend them.

[daytona98]

Well the guage used to work, stopped working when the heat stopped. why i think it's more mechanical than electrical gremlins. (jakecs) I.e thermostat/
So there is two sensors that It could be? the temp gauge sensor which I'm guessing control the gauge on the dash? or the coolant temp sensor which control the electirc rad fans? Since the fans operate normally i'm leaning towrads temp sensor. Either way I'm doing rad flush and new t-stat.

Dr.Dodge, does the sensor with one pin connector have like a threaded portion on the top to screw the connection and the rest of the brass part goes in the block?

[Dr. Johny Dodge]

yep that's the one for the gauge

might be an idea to try pulling it out of the head and see if any coolant comes out

if not the head is dry - without coolant touching the sender you will never get a temp on the gauge - + the over heating issue

[daytona98]

Well the coolant level in the rad and overflow at correct so I doubt the head is dry since it circulates from the rad no? I'll try the tstat and the sensor you mentioned, see if that helps. Hopefully fixes having no heat in the winter an garbage mileage.

[ILIKESHELBYS]

+1 on the O2 sensor causing the bad gas mileage. Been there, done that, twice. No codes at all, seemed to be running fine, but less than 10MPG.

[ChargedDust]

You may also want to check the heater control valve, IIRC there is a small vacuum line that goes to the valve which opens it allowing coolant to the heater core. +2 on the O2 sensor for the poor mileage, my experience is that they do give you fault codes, I've had to change several.

You could have multiple issues, if in fact the engine isn't heating up, then the computer might be seeing this and keeping the fuel ratios at cold start, which for an extended period of time may have fouled out the O2 sensor.

Personally, I like the Stant Superstats, stay with the factory recommended setting (195º I think) for proper heat. Also remember that the coolant system needs to be bled after. If you can get the plug out of the head on the top of the t-stat housing that is how you bleed it, many times they are badly stuck in place, alternately you can park on the steepest hill you can find and let it get up to operating temp, let the fan cycle on 2 or 3 times and you should be good enough.

BTW, you never mentioned if you checked for any codes....

[daytona98]

Thanks I shall check the heater controls and heater core as well. It's not throwing any codes hence why I'm playing guessing game haha. Not the best way to do it but w.e I think I'll do an o2 sensor as well, they are cheap enough on ebay. Should I get one or 2?

Charged Dust, After replacing t-stat, temp sensor etc, You mean fill the rad/engine with coolant and there is a air bleeder screw to get out any airlock?
Never had to do one like that before, just usually drain and fill

[Dr. Johny Dodge]

yes , C-D ment you can end up with an air bubble in the head when filling the rad

filling / running it with the front end on blocks will serve if you don't have a steep slope to work on

[daytona98]

Great thanks, will a 6x6 block of wood give me sufficient angle to avoid air lock? Or is there a trick like replacing thermostat and re attach rad hoses but pull temp sensor out of block and fill with coolant till it gets to the level where sensor it at? Then just stick in sensor and continue filling? Never had to deal with an airlock problem before, is that common with these cars/engines?

I def do not wanna deal with air lock or overheating problems that could cause more damage in the long run. Great advice everyone, sorry for all the questions that may seem silly.

[ILIKESHELBYS]

There is also the little trick of drilling a 1/16" hole in the thermostat and placing that hole in the 12 O'clock position when installed. This allows the thermostat to pass a trickle of coolant into the water box on the front of the head. That is where the air can and often is trapped and causes the coolant temp sensor (for the dash gauge) to move the needle about so quickly, its the hot water splashing on and off the end of the sensor. Another trick is to fill the radiator half way with coolant (not the 50/50 mix) and then pour in hot water (distilled is best since there are no deposits to fall out of it). When the hot water reaches the themostat it will cause it to open and the water box gets filled. The water will have to be at least 190* when poured obviously if you have a 190* thermostat.

All this assumes that the water box vent plug is not going to come out easily...and typically on a 25+ year old head they wont. If you use a torch to get the aluminum hot enough to swell (remember the coefficient of linear expansion of steel and aluminum are different) the plug can then be coaxed out of its home with a properly sized allen wrench socket. Not one that almost fits....you need a good snug fit to get the needed torque to turn the plug. Use the wrong size and you will quickly round the corners and removal at that point is going to be even harder.

The way I addressed this problem was a bit simpler, I just drill and tap the plug for a bolt (I like to use oil pan bolts) and then with the bolt and either a oil drain seal (plastic) or an copper or aluminum washer under the bolt to act as the seal. It works great and in the future it is easy easy easy to open and bleed out the air. You can go one step further and actually get or make a bleeder screw so that you dont even have to remove the bolt. I did this by chucking the bolt up in a clamp and then drilling a hole about 3/4 the way down the bolt from the end (not the head) and then drilling a cross hole to meet with the first hole. The cross hole I placed about 1/8" under the head. So to bleed w/this setup, you just loosen the bolt (not remove) and fill-er-up. When the bleed hole runs a solid stream of fluid, and stops bubbling/gurgling I know that all the air has been purged. The trick to this mod is to be POSITIVE that you drill and tap the hole square to the top of the plug or the seal ...wont. I actually used a fine file to be sure the top of my plug was flat and had a good sealing surface before I drilled the hole. If you are a little bit off when the hole is drilled, you can still use a file to lower the side of the plug that is too high and still get a seal....but its more work than required if you just make sure its flat to begin with and then drill a hole square to the sealing surface.

[Dr. Johny Dodge]

sensors are a little to low in the head's water jacket to get the air out of the top
that's why there's a plug in the top of the box at the T stat - that's usually stuck

but try takeing it out , you may get lucky

6x6's would be a start but I'd prefer a couple of cement blocks as they would be a bit taller and would be a little safer as the contact patch to the tire would be bigger

squeezeing the rad hoses to burp the system will help to - in fact it's all I ever have to do

[BobD]

+1 0n the drilling the hole on th top of the thermostat. Sticky back gasket helps big time in the alignment of the hole.
I may have missed it, but is your Daytona, a TBI or Turbo?
If a Turbo, be careful with the O2's you use. A lot of guys only use Mopar ones because the rest don't always work. I've wasted my money on a Bosch that did absolutely nothing. (frustrated me for a year wondering why I still only got a little over 10 mpg. 2.5 turbo Shelby Daytona) You can save a lot of money getting a NTK (made by NGK) They are an exact drop in. They make the Mopar ones. This is with a Turbo. The TBI's aren't as picky and another brand and may work just fine. The NTK's can be bought locally for under $40 if I remember correctly. Mopars were like $110 6-7 years ago.