Al's 1993 Aerostar XL (Green)

[asavage]

Speedo reading vs . (borrowed) Magellan GPS:

Speedo      GPS
10          09
25          23
35          33
40          38
42-3        40
50          47
54          50
60          55-6
65          60

The speedo is analog but electrically driven. There is a recalibration process that one can do -- a calibration constant is changed, it's a number, you change it using the Select and Reset buttons on the speedo -- but you only get six changes per lifetime, and after that it can't be changed.

Current constant value is 995.

I am having trouble determining how much to change that number to get the desired result.

[kassim503]

I think the constant value would have to go lower for it to read slower

Ford Speedometer Calculator This could work, it probably wouldnt, it probably uses the forumla ford created and would probably still give u 5 under, plug in your info and play around with it, see if its accurate or not.


On the PSOM you lock in the code by pressing the reset button at the end, I have never tried this idea that I just cooked up, but you may be able to test drive with different constant values, ground out the connector, start the car, change the constant value, cruise around and compare with the gps, lock it in once your happy, and that may be it. Would it work? probably not.

If that worked people would probably cut the math out of the equation, and the psom would be the greatest system to ever hit the face of the planet.

I wouldnt bother with any of it, having a speedo that reads 5 high is great, you can do "75" in a 65 and probably not get a ticket, and even though you are still going slower than traffic is, your dashboard is screaming haulin ass

[Carimbo]

I am having trouble determining how much to change that number to get the desired result.

You could call Puget Sound Radiator & Speedometer Repair - (206) 524-0886.
Seems like they would be dealing w/ this all the time.

[asavage]

Random leftover pictures
These are pictures that I didn't use in the main post.






I was experimenting with plumbing washers and actually found a couple that would probably work on the PS lines, if the temp didn't get too hot.

[asavage]

Investigating the wavering and low-reading temp gauge.

The FSM says to test the gauge using resistors.

9.5 ohm = "C" mark
74 ohm = "H" mark

At 12.4v, I used 10 ohm and 76 ohm (closest I had in my junk bin).


A bit low on both ends. Doesn't explain the wavering though. New temp sender. IR gun results inconclusive. Tried a fourth thermostat: no change. Well, actually, average is a bit lower if anything.

Why do I get all these extremely-weird problems?

[rlaggren]

Do the IR thermometer and the dash gauge move the same?

On most of my vehicles when the temp gauge moves more than about 1/8 scale, I can feel it in the heater air temp. Maybe that would give a hint whether the fluctuations are real or electrical.

Rufus

[plenzen]

I know this is going to sound weird but here goes. I had this similar problem with a Mercury Lynx that I owned. I finally figured out that if the gas tank was more than half full then the temp gauge would give me one reading and if the tank was less than half full the temp gauge would give me another reading? ( I cant remember which way it went though) I aint kidding, that really was the case. I don’t know if the resistor behind the dashboard or where ever it was located did the "resisting" for both or not, but that the reading of one did affect the other. I finally got tired, frustrated actually, of trying to locate where the problem was an installed a mechanical temp gauge. The engine temp was in fact normal and stable on the mechanical gauge when it was doing its "fluctuating" with the dash gauge. I changed sender on the temp gauge at least once, and I did not even bother with the tank gauge as it would have meant breaking off a bunch of rusted things to get at it. Have you tried installing a mechanical gauge temporary to see if in fact the engine temp is actually fluctuating and that you are not being tricked?

Paul

[asavage]

This dash uses four similar gauges. They are "magnetic" gauges, no springs, non-thermal. The other three operate without anomalies. There is no voltage regulator in the dash, as there were in Fords of years past that used thermal gauges.

The low reading I can understand: there may be a high-resistance joint in the line from the gauge to the sender.

But the wavering isn't so simple. I have had an ohmmeter on the sender; perhaps I should run a wire around and mount the ohmmeter on the dash for a few days.

Data from the IR thermometer is difficult to interpret, as different readings occur depending on where you "shoot". But it does seem to indicate actual temperature fluctuations that are much wider than normal. I'm beginning to look for oddball things like the wrong rotation water pump installed, or a small combustion leak that introduces a small amount of gas in the coolant that makes the thermostat act oddly. Out there stuff, but I've tacked the obvious areas already.

Instrument clusters are $17 at the JY in Tacoma, I'll pick up a spare and swap the whole thing, at the same time I can "use up" the speedometer constant changes on the JY cluster, zeroing in on the correct value on a throw-away PSOM module -- one gets only SIX changes per PSOM, period (until after 1997, urg).

[plenzen]

Al. I found this, (quote below) and I know the years are different, but I could not get access to earlier years without buying a subscription. There were similar complaints for earlier years and Aerostar in particular. The first link to the site below lists "TSB's" for this problem but no descriptions available without subscription.
Dont know if this will help you or not.

http://www.aboutautomobile.com/tsb/1994/FORD/AEROSTAR

The below quote came from here:
http://www.rebuiltautoengines.com/ford- ... icles.html
It cites nearly the exact wording for the same problem with the Exploder!
FWIW
Paul

Temperature Gauge Fluctuation On
1995-2000 Ford 4.0L OHV Engines

AERA members have reported a temperature gauge fluctuation on 1995-2000 Ford 4.0L OHV engines. Along with this fluctuation, the customer may complain of a knocking or thumping noise as well.

This noise is most pronounced with the engine at normal operating temperatures and heard in the passenger compartment of the vehicle. The noise is caused by steam formation in the cooling system. This noise is then transmitted through the heater hoses and heater core.

Ford offers a Coolant By-Pass kit to cure this problem. This kit increases the flow, which reduces steam formation in the cooling system. Refer to the chart listed below to get the correct By-Pass kit as it depends on the type of vehicle the customer has.

[asavage]

That's for the 4.0l, which is an entirely different critter (no parts interchange with the 3.0l).

Both my '93 and my '89 have exactly the same engine, same heater hoses, same water pump and same heater core, and did not show any fluctuation or reading low. However, the '89 has the optional digital dashboard, which coarsens the gradations on the display, so minor fluctuations do not register.

If I do not purge the cooling system of air completely, I can hear very odd noises from the heater core: gurgling, whooshing, etc. But it's silent if I follow Ford's purge procedure.

I have run this 6k miles and it hasn't changed, hasn't been using coolant either. Any air in the system would have been purged by the heat/cool cycle and the reservoir. But if new gas is being introduced at cooldown, by some leak I don't know about and which is not showing at the radiator fill neck as low coolant, that would explain at least the odd warm-up behaviour (warms to setpoint, then the needle drops like a rock to almost 'C', then slowly climbs to somewhere lower than setpoint and then varies from too cool to much too cool for as long as I drive).

The later ('94? 95-on?) Aeros all have an integrated bypass/enable valve on the heater hoses to allow shutoff of the heater core during Max A/C operation, but these earlier Aeros don't, they run coolant through the core at all times.

[plenzen]

It certainly behaves like thermostat problems. Are you using one of those "fail Safe" ones? I have had issues with those in the past at allowing things to run too cool, not remaining shut, sticking etc etc.
I changed three in a row in a 3.1 V6 GM before I finally went to the Delco one and problem solved. I guess I could have just as easily gone to a Stant "non fail safe" one too.

Paul

[asavage]

Four thermostats:

1. The one it came to me with;
2. A NAPA (Stant) SuperStat (non-fail-safe);
3. An OEM Motorcraft (ordered through the Ford dealer);
4. A cheap NAPA 183

All give the same symptoms, though thermostats one and four read lower average than the other two.

I have thermostats two through four on hand.

[plenzen]

You definatly have a puzzle on your hands. Hmm?? It is not one of those thermostats that has the rubber gasket around the perimiter of it is it? Or is it supposed to have one of those rubber gaskets around it. Almost seems like it is lifting in the housing when it gets hot enough and has to open, and then perhaps moves or tilts upwards to allow bypass. ,,,,,, Is the coolant actually cold or is it just the guage that is telling you that it's' cold? If it were me, ( and I know it is not) I would somhow, some way install a mechanical guage and see for sure if in fact is is cooling off and its just not the dashboard guage screwing with your inner peace.

Paul

[asavage]

It is not one of those thermostats that has the rubber gasket around the perimiter of it is it? Or is it supposed to have one of those rubber gaskets around it.

No rubber gasket. Assembly order (click on image for larger):


Note that the gasket does go on the opposite side of where most t-stat gaskets reside -- there is a recess in the outlet housing, not the manifold. I've been assembling it correctly.

Almost seems like it is lifting in the housing when it gets hot enough and has to open, and then perhaps moves or tilts upwards to allow bypass.

Thermostat No. 3 I RTV'd into the outlet housing, let it set up, then assembled: there is no possibility that any coolant made its way around that thermostat, definitely not, and I had to pry it out when I put t-stat No. 4 in place a few days ago: it was not moving around.

Is the coolant actually cold or is it just the guage that is telling you that it's' cold?

That is the Q, isn't it? And, if it's not cold, why is the gauge moving up and down as if temp variations are happening?

If it were me, ( and I know it is not) I would somhow, some way install a mechanical guage and see for sure if in fact is is cooling off and its just not the dashboard guage screwing with your inner peace.

I do not trust mechanical gauges any more than electrical ones, I've had too many weird readings from mechanical gauges to believe they are "better".

However, when I buy a JY cluster, I will have another shot at it.

Meanwhile, rigging a temporary ohmmeter to the (new at Christmas) temp sender gives me a second gauge, since the output of the sender is supposed to directly relate to the temp it senses.

I'm also thinking of cutting the upper hose and putting in a clear section of Lexan. If I don't learn anything, at least it's bling .

[plenzen]

I just thought that the mechanical gauge would be another way of getting a temp reading that did not rely on grounding to the block, or any kind of electrical device(s)/systems etc. as the coolant/temp. sensor does. I thought just for a reading that is all, not necessarily permanent. Speaking of which, and I know I am waaaayyy out there on this one, but, what did you use to seal the coolant/temp sensor? Perhaps the sealant or whatever is insulating from a proper/good ground. Maybe run a jumper wire from the outside of the sensor to the (-) side of the battery. Long shot I know. It sure acts like that problem that I had on that damned Lynx though and it was something else that was affecting the temp guage. Oh yeah I almost forgot. The clear piece of Lexan will be cool ( no pun intended) Picture of that please.

Paul