Engine Running hot and driving me crazy

bad_decision

Member
Aug 14, 2020
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Houston, TX
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
Aug 25, 2016
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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
253
128
53
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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Memphis TN
In cool weather mine runs about a notch below center....in hot weather, it about in the center....
 
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KRUISR

5 Year Member
Apr 16, 2015
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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

Member
Aug 14, 2020
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Houston, TX
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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Sep 1, 2010
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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
9
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37
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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