Engine Running hot and driving me crazy

bad_decision

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Aug 14, 2020
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I picked up a 91 LX Convertible about 6 months ago, and one thing that has always annoyed me is that it runs a bit hot according to the stock temp gauge. The needle fluctuates between the mid point and the next tick up, something my previous fox never did. The motor was pretty much untouched by the previous owner and I'm guessing it is high mileage. As I want the cooling system working as well as possible, here is what I have installed:

New coolant temp sensor
SVE Aluminum Radiator
Gates reverse flow water pump
Motorcraft 195 degree tstat and fel pro gasket (no rtv or silicone)
New factory style fan, kept the stock fan shroud as-is
Haven't replaced the fan clutch, but it appears to be working as expected
Two 'at-home' flushes via drive cycles
Bled air with the front jacked up

When driving it, sometimes it gets hot at idle and sometimes when I'm cruising. It is inconsistent. It will randomly cool back to normal... both at idle and when cruising. The heat blows warm but NOT HOT - measured a little over 100F on my infrared temp reader. The tstat housing reads 200-205F once it gets warmed up good. No leaks that I can see. Compression is 130-135 psi on all cylinders. Based on the smell of the car I do think it is running rich if that matters. The only code is EGR related, haven't figured that one out yet.

I really don't know what to try or test next!
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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As I've said in the past, install a mechanical gauge, even temporarily zip tied to the wiper arm or something, compare those readings to the stock gauge and you will know if you are really running hot.
 
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HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
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From your infrared readings everything's fine. A little above the middle is no big deal.
 
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91AOD5.0LX

I have a slight sag in my rear
Feb 20, 2021
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Mine is always between the middle notch and the next one up. I believe that’s normal. She Runs fine.
 

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91AOD5.0LX

I have a slight sag in my rear
Feb 20, 2021
333
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North East
That's where mine is..Thanks good to know. My old one was bad..Maybe. It doesn;t seem that hot
I’d love for it to be dead center. Sometimes it is but most of the time she rides a little bit higher as shown in my picture. Never had any problems so decided not to let it bother me but always keeping an eye to see if it ever increases. That’s why I keep that picture so I can always compare.
 

HemiRick

I'd be looking at jacking under the house
Jun 28, 2020
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In cool weather mine runs about a notch below center....in hot weather, it about in the center....
 
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KRUISR

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I converted to electric fans and they come on at 205. My OEM coolant sensor would show the fans come on at the middle point (as you described). Unfortunately it crapped out and I put in a replacement. I changed nothing else in the system (same fans, same controller, same t-stat). My gauge will now climb to the point shown in the pic above, maybe slightly higher to the O, but my system still cycles as expected and I don't overheat. I have just come to expect that this is the new normal.
 
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bad_decision

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91AOD - that is exactly where mine sits! I was a little bit worried just because sometimes it can go back to dead middle at any point. Good to hear it is not uncommon. I may hook up a mechanical gauge just to get a more accurate number for peace of mind. Right now I feel like I'm always looking at that gauge!
 

7991LXnSHO

wanna catch the space herp
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I agree that it sounds fine, but aftermarket gauges are a good idea for oil pressure and coolant temp,
Any reason you did not replace the fan clutch but did replace the fan? Was the fan damaged or a flex fan?
Is the lower air dam in place?
 

bad_decision

Member
Aug 14, 2020
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Houston, TX
When I start replacing things on my car, I walk a fine line between replacing everything I touch and doing preventive maintenance :O_o: It had a stock fan but the blades were cracked, and as far as I could tell the thermal clutch was working as expected so I didn't think it was necessary to replace it as well.

Yep, lower air dam is in place as are the deflectors on both sides of the radiator.
 
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pavlos413

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Jul 26, 2021
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Mine is always between the middle notch and the next one up. I believe that’s normal. She Runs fine.
Mine has been running hot lately too, I recently installed a highflow water pump, new radiator and thermostat, new engine and coolant temperature sensors, and underdrive pulleys I was getting really worried. I tried burping the system once, I'm going to try again hoping that will do the trick to lower it a bit. I'm also going to add a Royal Purple additive to see if it helps at all. Oh and my rubber flaps as well as the piece under the car are shot, so I ordered new ones hoping that'll help.
 

2000xp8

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Aug 8, 2003
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Mine has been running hot lately too, I recently installed a highflow water pump, new radiator and thermostat, new engine and coolant temperature sensors, and underdrive pulleys I was getting really worried. I tried burping the system once, I'm going to try again hoping that will do the trick to lower it a bit. I'm also going to add a Royal Purple additive to see if it helps at all. Oh and my rubber flaps as well as the piece under the car are shot, so I ordered new ones hoping that'll help.
Why a high flow water pump?
IMO, don't put additives in the cooling system.
Lose the underdrive pullies (The 5hp they give you do more harm than good).
Buy a motorcraft or ford racing pump, i think they are like $75.

Between the pullies and the hiflo water pump, you messed with too much at once. Who the hell knows volume or speed of the coolant flow.
 
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7991LXnSHO

wanna catch the space herp
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The tractor version and this higher price racing version of water wetter are helpful. 5-10 deg on a functioning coolant system is what I have seen. It is mostly a surfactant so the water makes better contact and transfers heat better.
It will not fix a bad system, but gives more heat transfer in a good one under HD conditions.
 

KRUISR

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Pavlos... what do you define as hot? You may have no issue and just a factory gauge showing you a high number (that is incorrect).
 

2000xp8

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Aug 8, 2003
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The tractor version and this higher price racing version of water wetter are helpful. 5-10 deg on a functioning coolant system is what I have seen. It is mostly a surfactant so the water makes better contact and transfers heat better.
It will not fix a bad system, but gives more heat transfer in a good one under HD conditions.
I think the real question would be, if you have a properly functioning cooling system, why would you need water wetter in the first place?

Also, water wetter has been linked to gunk and sludge in the system. Has this been proven 100%? I'd say no, but i think it happens too often to ignore it.

A good 3 row, properly working fan clutch with stock pump is reliable and effective.
Too often people make more problems than they fix by messing with the cooling system.
 
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7991LXnSHO

wanna catch the space herp
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I think the real question would be, if you have a properly functioning cooling system, why would you need water wetter in the first place?

Also, water wetter has been linked to gunk and sludge in the system. Has this been proven 100%? I'd say no, but i think it happens too often to ignore it.

A good 3 row, properly working fan clutch with stock pump is reliable and effective.
Too often people make more problems than they fix by messing with the cooling system.
That’s why I’m picky about what additives I use. If you live in a climate where water only works during race season, something with anticorrosion is needed. Otherwise, it’s a bit of margin on really hot days or an extra heavy load.
 

pavlos413

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Pavlos... what do you define as hot? You may have no issue and just a factory gauge showing you a high number (that is incorrect).
It's above the middle line, sometimes it's halfway to the next one above and sometimes it goes to the line right above middle and that's scaring me a little especially because there's no numbers on that guage below 270 and I'm wondering how hot this thing is actually getting. I think I'm going to get a temp laser scanner and check the thermostat and the hoses to read where it's at.
 

7991LXnSHO

wanna catch the space herp
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For best results, use the temp gun on metal parts. They conduct heat better than rubber or plastic.
 
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