new cat + exhaust = overheat??
 

hey, ok i have a strange problem... in an attempt to cure my glowing exhaust (aftermarket) and turbos, i took the car to a muffler shop. they took a heat reading before and after the cat and verified that (as suspected) i had a clogged cat. so i had a spare cat w/ 93K miles on it which i swapped in place of the old one. it smells like the cat isnt cleaning the exhaust as much as before (smells like a slightly cleaner midpipe), but i have some increased power (with some strange hesitation around 5K) :confused: .

now the car overheats in traffic, and will also overheat if im on boost for awhile and then slow down (on the highway)... im getting the coolant buzzer a few times a day :( , and have had to pull over to the side of the road and wait for 1/2 an hour so the motor didnt get cooked.... so something is VERY wrong. (and yes i have checked and topped off the coolant)./ the engine bay is EXTREEMLY hot..... what the hell happend?? i changed nothing but the CAT. BTW, the packing inside the exhaust still glows, as do the turbos... but only after boost now (its definatly not as bad as before).

im thinking about getting a HF cat, KOYO, and miata thermo sensor....but i have a feeling im just gonna mask whatever problem is there unless i sort this out before the new stuff goes in. also, it may be a few months before i can purchace the new cat and radiator. oh yeah, one more thing... i now have horrendous gas mileage. any ideas??

anyone???? im to the point where im considering taking it to the mechanic because the motor will not last much longer going like this

have you checked the downpipe? there's a cat in that too. if not, replace it with an aftermarket downpipe.

Wait, you said your coolant buzzer is going off? That sounds like a coolant leak.

its not the cat dude, your missing the big picture. Get a new downpipe instead of wasting more money on cats. Also it wouldn't hurt to get a bigger radiator like you said since you probably will do that later on anyways. But getting a new downpipe (aftermarket of course) will probably fix it. If this doesn't fix your problem, then your exhaust isn't the problem at all. It may lie as a coolant leak, which may be your turbo coolant lines which would cause your turbos to glow along with exhaust.

well i dont have a coolant leak because im no loosing any coolant. i have an aftermarket DP, so thats not hte problem.... any more thoughts??

but if it was a coolant leak on the turbos it would evaporate before you could see and also would cause overheating.

Are your fans coming on? An FD will overheat sitting in traffic if the fans don't come on.

If your coolant buzzer keeps going off, you have one of two problems. You are low on coolant, or the sensor is malfunctioning. Which is it?

you swapped a used cat for another used cat. Perhaps it was the greater of two evils.

i think there is a buzzer for over heat exhaust too

so it might not be coolant.

I ran my car with only a dp once and it started yell'n at me b/c it was getting too hot me thinks.

adam c: i believe the first fan is coming on... im not sure about the 2nd (it will turn on if i put the AC on... but really once i see the needle move enough for me to notice its hard to stop the overheating if im not on the highway).

i never thought about the meaning of the "low coolant" red light, as i always just associated it with overheating.... the reason why i just thought of the red light as the "your car is overheating....turn it the fuck off" light, is because once the car is cool the light will go off... and when i checked the coolant it would be at the normal level.

Sesshoumaru: yes :biggrin: i swapped a used cat for another used cat... i was leaving for a long trip so i needed my dads car (so we swapped for a week).... i didnt want to send him off with a car where the exhaust was glowing red, for an entire week..... so i swapped the cat, but unfortunatly that made the car overheat


basically im fucking sick of the car... i have been doing nothing but chasing problems since i got it (and i know that once everything is fixed the motor will give out). i just found today that it smokes a good amount at high RPM's (which it did not do before i swapped cats). the smoke is white/blue so it could be oil, or maybe just the cat not doing its job (where maybe before it was clogged but still scrubbing the air)??? one thing after another :mad:

This may sound dumb -- but are you checking your coolant level at the filler neck and not the overflow tank?

Also, I'm going to take a guess and say it is your coolant level sensor that is malfunctioning. You say that your coolant levels are FINE, yet the sensor goes off once in a while. I'll bet that once you replace that sensor, that it'll fix things. Trace the wire back to the connector -- make sure it's clean.

Once that is fixed, go on to your hot exhaust. Swap the "new" cat out with your older one and see if your problem with the "hot" engine bay goes away. It may just be in your head that the engine bay is hotter than it used to be, as the engine bays do usually run really hot anyways (especially with the stock pre-cat).

Your poor fuel consumption may be due to quite a few things: your driving style, seasonal gas mixtures, your plugs, fuel filter, etc.. If the fuel consumption has gone down hill AS OF LATE, it might also be due to the "new" cat that you just put on, as it might be causing excessive backpressure (thus causing the glowing exhaust and the poor fuel consumption). Mainly, change back to your "old" cat, and see what happens. Oh, and now would be a good time for a high-flow cat/downpipe/boost controller.

Honestly, I have been where you are. When your car is not working the way you want it to work, you feel as if ditching the problem will resolve the situation. Once you get all these "minor" things squared away, you'll quickly chamber that angst that you once felt so strongly about.

well i checked the coolant level at the AST, filler kneck, and overflow tank.... each were slightly low so i topped them off.... i will check again to see if the levels are the same.

im ordering a new cat today so hopefully that will eliminate the hot exhaust.

im not sure why the fuel consumption has dropped so drastically though.... im going to do plugs, wires, fuel filter... and see if that helps.

thanks for the help walien... i noticed that you are in SLO... it seems like there are a good number of people with FD's there :wink:

Do you have the stock ecu? If you have another ECU, have you or anyone been "tuning" lately?

I ask because it almost sounds like you're dumping unburnt fuel into the exhaust. That would definitely make turbos glow more than usual (fuel burning in the turbo instead of the engine) and it would send your mileage to hell. It could also explain your clogged cat with unusually high heat and unburnt fuel melting the cells in the cat together. Did you cut apart your old cat to see/verify the damage?

It could also be that you might have a leaky fuel injector and that it's dumping extra fuel into the engine. Has it been hard to start at all? That's a trait of a car with leaking injectors also.

Just more stuff to think about.

nope its a 94 CA stock ecu... i have a spare that i could swap and see if it makes a diffence. nope, it hasnt flodded yet... starts up every time. i may be running rich or lean (but its the stock ecu so i wouldnt expect that).... could it have anything to do with an old O2 sensor?? im not sure the last time that has been replaced.

another think i notice is a dip in power (at full throttle) at around 5.5K RPM's.... im not sure if its related but it never did this before all these other problems started. hmmmmm

i will cut apart the old cat and see whats inside though.... ill take some pics and report back, maybe that will help in diagnosing.

/\ as was said verify that the fans are coming on.
make sure you have no air in the cooling sys
yes a lazy o2 sensor that is showing the ecu the lean side will cause a drop in economy and power due to the richness

Dude you need a new thermostat...
And while your at it get a mid-pipe, cats are stupid...
Oh yea then get a PFC...
Trust me though Id be willing to bet your thermostat isnt opening up and thats why you are over heating...

no, cats are not stupid!!!! i wish more people on this forum could understand this. A#1 it pollutes the environment, B#2 you will smell like exhaust every time you drive your car (at least thats how it is for me right now... it permiates my clothes) C#3 you dont want to breathe that shit in!!!!

if you are worried about performance loss get a knightsports metalit cat (same flow as a midpipe and cleans the air)!!!

as far as the t-stat, yes that is a possibility... i will replace it when i go all crazy trying to fix this overheating problem. PFC... no thanks. a miata thermo switch and a koyo should do just fine. i dont want any more performance from this car... i want reliability!! i have a 93 project car and a 20b waiting to go in... no need to go all crazy with the stock FD cause the performance sector is taken care of :wink:

BTW this is slightly off topic but what should my oil pressure be at idle and at high RPM's?

If the stock gauge is accurate then I show just over 100psi.

Mazda doubled the pressure I believe from 30-60 to 60-120 on fd's since at high rpms the eccentric shaft would be starved.

I second the cat. I just put one back on my FC after having a presiliencer for 3/4 year. Boost control is easier too. It also quiets it down which is what I want. Plus the others things he mentioned.

60psi????? zuh?? uh oh... i just checked my oil and its full... but i get 30psi @ idle, and ~60/70 at full throttle if i remember correctly...... its MUCH higher when the car is cold though (obviously)..... im quite worried

https://www.rx7club.com/showthread.p...pressure+stock

it is 30

fc's 30-60 and i guess they only doubled the top side to 120.

couldn't remember

Your oil pressure is fine.

oil prressure is 50 psi at 3000 rpm using something better than the stock gague.