On stock 91 GT - question on OEM cat system -

MrPerfect2 · Jul 29, 2019

My car is a all stock daily driver - with historic tags , so no emission testing - it has some borla mufflers on it that sound like a quieter version of 2 chamber flows ( without the drone or popping ) the cats seem original ( 105k miles on car ) looks like 4 cats on there ( I heard the front 2 are actually “pre heaters “ for the real cats closer to mufflers - can the front 2 get removed without causing the ECU to go into safe mode and cause the car to not run good ? I am looking to drop the operating water temperature down a few degrees and have heard a free flowing exhaust helps engine run cooler - got a new 192 thermostat , new fan clutch and stock shroud - I imagine the exhaust will get a bit louder too , but that is ok .

Wayne Waldrep · Jul 29, 2019

A couple of things. Is that temp reading on the gauge you are showing the temp you are trying to make lower? That is a very normal level. But, I looked at all my thermostats the other day so this is fresh on my mind. I run a 180 in mine. In the old days, I ran the must have 160 which did nothing for me. Then I went back to the 192. I've settled on the 180 now and it's working fine for me. Depends on your car though. As far as the cats go, I've knocked tons of them out when we used to do that and never once seen any difference in the front two compared to the rear two. But to answer your question, I knocked mine out and ran it that way for 20 years until I finally got an aftermarket x-pipe. Actually, I had a MAC Prochamber first then an X. Never caused me any trouble but didn't make the car run any cooler either.

MrPerfect2 · Jul 29, 2019

I can maintain 190-200 on 85 degree days - but when air temps in high 90s it goes to 220 after 45 min drive ( I can knock it down to 215 by running heat - with top down ) do you think a 180 degree stat would help - my view is the 192 would be fully opened anyway , so I can’t see that bringing temps down . If I cut the front 2 cats off it will still have back 2 - I think the air feed and O2 sensor are in the rear area ( can’t remember off hand ) the ECU should not notice front 2 missing correct ?

Wayne Waldrep · Jul 29, 2019

The O2 sensors are in the front on a factory pipe. Look at it this way, you can slap an offroad pipe on and it doesn't change anything so do whatever you want with the cats as far as the car goes. I've never had a computer notice and I've always done all 4 at the same time. Back then it was just an initial ritual for us to take them out, bump the timing, remove the silencer, put in a K&N air filter, and a couple of other things. As far as the thermostat goes, there probably won't be that much difference between the 180 and 192. Since you have the 192 just use that. How is the rest of the cooling system? Radiator? Waterpump? Tiny little air deflector under the radiator that's been off of my car for decades but everyone always asks about? Bottom radiator hose in good shape and not collapsing? Anybody else have any ideas for him?

FastDriver · Jul 29, 2019

1st, there is no issue. 220 is perfectly fine on an all iron motor. Hell, on aluminum motors, the on-temp for fans on the LS1s is 226*. Goes on high closer to 240*.

2nd, if you want the car to run cooler, you have an air-flow issue, or a heat exchanger issue. I would recommend a griffin 2 core radiator.

Cats aren't going to bring temps down unless they're clogged.

MrPerfect2 · Jul 29, 2019

It has the bottom air deflector on it . The radiator looks like it’s been changed about 5 years ago but hard to tell ( it does have good flow inside when I took cap off to watch ) , water pump looks about 5-10 years old , belt looks shiny so maybe there is some slip there - I will take a closer look at where sensors are - they should be after cats correct ? If there are not 4 sensors then 2 cats should suffice as far as inspection ( if I want to sell ever )

MrPerfect2 · Jul 29, 2019

FastDriver said:
1st, there is no issue. 220 is perfectly fine on an all iron motor. Hell, on aluminum motors, the on-temp for fans on the LS1s is 226*. Goes on high closer to 240*.

2nd, if you want the car to run cooler, you have an air-flow issue, or a heat exchanger issue. I would recommend a griffin 2 core radiator.

Cats aren't going to bring temps down unless they're clogged.

MrPerfect2 · Jul 29, 2019

Thanks for input -I heard iron heads can take more heat , but several of responders on my other thread about normal temps said 220 was approaching danger .

FastDriver · Jul 29, 2019

That's pretty conservative, and it's a parroted rule of thumb, and not a bad one, as people will push it, anyways. That's also where I get concerned on my own setup with aluminum heads, but it's because my car runs from 188-213, and it has a LOT of cooling capacity beyond what the motor generates at anything but sustained high loads. So, when it gets to 220*, something has gone wrong. That's by my design. 185* t-stat, fan kicks on at 205*, have only seen 213* once, and drops back down to 195* when the fans shut off. When I cruise it drops to 188*. That gives me almost 20* for the car to get through a red light without kicking the fans on.

I don't really worry about warping or damage until over 240*. Even that's conservative. I remember getting my AFRs so hot they cooked the oil, which would require oil temps of 270-300* (hotter for synthetic). The heads were still fine. I don't know how long it ran that way. My buddy was driving, and I woke up, looked over, and noticed the temps were over the top of the stock temp gauge. The car lost oil pressure over the next 10-15 minutes. I thought the mains were toast, but after putting fresh oil in, the pressure came back up, and there were no issues anymore. If the heads warped, it wasn't enough to cause leakage past the headgaskets.

nickyb · Jul 29, 2019

You could drop temps with a electric fan and some water wetter,I'm in hot as the sun Nevada and in traffic with a.c. On I stay 200 or under. P.s. It's 113 degrees today,yes that's 113 ! Stay cool my friend.

MrPerfect2 · Jul 30, 2019

FastDriver said:
That's pretty conservative, and it's a parroted rule of thumb, and not a bad one, as people will push it, anyways. That's also where I get concerned on my own setup with aluminum heads, but it's because my car runs from 188-213, and it has a LOT of cooling capacity beyond what the motor generates at anything but sustained high loads. So, when it gets to 220*, something has gone wrong. That's by my design. 185* t-stat, fan kicks on at 205*, have only seen 213* once, and drops back down to 195* when the fans shut off. When I cruise it drops to 188*. That gives me almost 20* for the car to get through a red light without kicking the fans on.

I don't really worry about warping or damage until over 240*. Even that's conservative. I remember getting my AFRs so hot they cooked the oil, which would require oil temps of 270-300* (hotter for synthetic). The heads were still fine. I don't know how long it ran that way. My buddy was driving, and I woke up, looked over, and noticed the temps were over the top of the stock temp gauge. The car lost oil pressure over the next 10-15 minutes. I thought the mains were toast, but after putting fresh oil in, the pressure came back up, and there were no issues anymore. If the heads warped, it wasn't enough to cause leakage past the headgaskets.

MrPerfect2 · Jul 30, 2019

You would not worry as much with iron heads on a stock set-up ? Another question I have is why Ford put the # 270 on the stock gauge as danger area?

Mustang5L5 · Jul 30, 2019

I don't think cutting the two front cats off will do anything for cooling your engine. This is really a bandaid solution.

If you are really concerned, then address the cooling system with either a new coolant flush, or a new radiator, or install deflectors alongside the radiator to channel flow through it better. Also, make sure your fan clutch is in great shape and has resistance when you spin it by hand (engine off of course). When those go bad, they tend to freewheel loosely and don't pull as much air through the radiator.

My car will run 188 degrees all day long with the stock 4-cat pipe in place.

FastDriver · Jul 30, 2019

Yeah, I'm sorry. I guess I wasn't thinking straight. 240* is the number I think about for aluminum heads. 270* is Ford's danger area. I would say that if you're operating in this range (coolant temps), you should be pretty worried about your oil temps, which can often exceed the coolant temps. Beyond 270*, you're cooking dino oil.

General karthief · Jul 31, 2019

Beyond 270* everything is cooking!
Without going back through the thread looking for symptom/repair suggestions let me say a couple things, a plugged cat could cause higher than normal engine temps, there would be other symptoms too like sluggishness and the smell of burning hair when the neighbors cat slips underneath the car.
More likely high engine temps are a flow problem, I test all thermostats before installing because well, most just don't work in the operating range they say they do.
The fox temp gauges are a little on the ahhhh, lets just say they are a hint of what the temp is. Mostly because of age and wiring condition.
A good radiator, fan clutch, shroud and the air dam under the radiator support should keep the temps at reasonable levels, I would say 195 to 220* or even 230* sitting in traffic with the ac on is reasonable.

MrPerfect2 · Jul 31, 2019

Thanks all for your input ! Highway cruise at 1900 rpm for 30 min at 65 mph yielded 230 temps in 95 degree air temps / high humidity ; same trip today yielded 218 temps but air temp was 82 degrees . It seems higher rpm and higher speed makes my car run hotter than low rpm stop and go city driving . It has a new Hayden heavier duty fan clutch , so I would think the fan would spin hard as rpm rise .i am thinking either radiator not flowing enough or water pump not circulating enough , could be a sticking thermostat ( but that is a new Stant 192 ) maybe this is how stock mustangs temps run with OEM style parts ( probably not many stock mustang people on here , lol )

General karthief · Jul 31, 2019

Sounds like it may be time for a radiator and/or a water pump
didn't look but what is your timing set at?I
the fan clutch should free wheel (so to speak) at speed.

MrPerfect2 · Jul 31, 2019

Don’t know what timing is actually set at ( seems to run good - no bog or stutter - crisp throttle response , no ping or knock on 87 octane ) as for free flow spin , I know it does not spin at full speed of rpm - it’s next step up from standard duty ( heavy duty ) but below severe duty clutch

MrPerfect2 · Jul 31, 2019

MrPerfect2 · Aug 1, 2019

FastDriver said:
That's pretty conservative, and it's a parroted rule of thumb, and not a bad one, as people will push it, anyways. That's also where I get concerned on my own setup with aluminum heads, but it's because my car runs from 188-213, and it has a LOT of cooling capacity beyond what the motor generates at anything but sustained high loads. So, when it gets to 220*, something has gone wrong. That's by my design. 185* t-stat, fan kicks on at 205*, have only seen 213* once, and drops back down to 195* when the fans shut off. When I cruise it drops to 188*. That gives me almost 20* for the car to get through a red light without kicking the fans on.

I don't really worry about warping or damage until over 240*. Even that's conservative. I remember getting my AFRs so hot they cooked the oil, which would require oil temps of 270-300* (hotter for synthetic). The heads were still fine. I don't know how long it ran that way. My buddy was driving, and I woke up, looked over, and noticed the temps were over the top of the stock temp gauge. The car lost oil pressure over the next 10-15 minutes. I thought the mains were toast, but after putting fresh oil in, the pressure came back up, and there were no issues anymore. If the heads warped, it wasn't enough to cause leakage past the headgaskets.

On stock 91 GT - question on OEM cat system -

MrPerfect2

Wayne Waldrep

Before I post a pic, do you have one of yours?

MrPerfect2

Wayne Waldrep

Before I post a pic, do you have one of yours?

FastDriver

I was uncomfortably high & wearing a helmet

MrPerfect2

MrPerfect2

MrPerfect2

FastDriver

I was uncomfortably high & wearing a helmet

nickyb

I gotta say i never painted my nuts, Never Ever

MrPerfect2

MrPerfect2

Mustang5L5

That is…until I whipped out my Bissell

FastDriver

I was uncomfortably high & wearing a helmet

General karthief

wonder how much it would cost to ship you a pair

MrPerfect2

General karthief

wonder how much it would cost to ship you a pair

MrPerfect2

MrPerfect2

MrPerfect2

Similar threads

On stock 91 GT - question on OEM cat system -

Before I post a pic, do you have one of yours?

Before I post a pic, do you have one of yours?

I was uncomfortably high & wearing a helmet

I was uncomfortably high & wearing a helmet

I gotta say i never painted my nuts, Never Ever

That is…until I whipped out my Bissell

I was uncomfortably high & wearing a helmet

wonder how much it would cost to ship you a pair

wonder how much it would cost to ship you a pair

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