283 Maxidyne Exhaust Temps

[Lmackattack]

Im Looking for some people with a 283 maxidyne and 5/6 speed combo.

Whats your EGT reading at a hard pull?

whats your avg cruising EGT.

just wondering as im sometimes seeing some high EGT temps (1200.) after a adjustment of the fuel screw.

I also recently installed a new probe and guage. the wire lead between the probe and guage was standard wire. Im wondering if I need a special wire lead/ length or if i just have a little to much fuel going to her?

Whats the thought on this one?

[fullfuel01]

Trent, I'm driving a DMM mixer truck. 285 and a 5 speed. fully loaded on big hill never reach more then 950. at full speed ( 60mph@2125 rpm) on flat road it's something near 600. not sure at 100% of this one but I'll take a look for you. somebody already told me that you should not cut these wire. their lenght sould not be changed... I'm sure it's because the probe make it's own current so if you change the lenght you change the restristion of it... I know that the pump on my truck is turned up a bit, and I added some shims on the puff limiter cylinder.. black smoke is great!! bulls make dust with their paws, bulldog do black smoke by the exhaust!

[b61mack]

Trent, I'm driving a DMM mixer truck. 285 and a 5 speed. fully loaded on big hill never reach more then 950. at full speed ( 60mph@2125 rpm) on flat road it's something near 600. not sure at 100% of this one but I'll take a look for you. somebody already told me that you should not cut these wire. their lenght sould not be changed... I'm sure it's because the probe make it's own current so if you change the lenght you change the restristion of it... I know that the pump on my truck is turned up a bit, and I added some shims on the puff limiter cylinder.. black smoke is great!! bulls make dust with their paws, bulldog do black smoke by the exhaust!

Trent i have a 76 285/5 speed on a hard pull it has been running 1100-1150 EGT, on flat ground it will run 900-1000, you need to get the wiring,if you shorten or use differnt wiring it will not read right,1200 is too high ,1125 is max, i think my pump is getting worn out letting too much fuel in,you might check your air filter. Ron

[therabbittree]

well you mention the higher egt after a fuel screw mod..maybe you turned it up too much..it doesn't take much...other wise ya need a bigger turbo...

thanks

deo

[Lmackattack]

Thanks guys

I gave the screw about a full turn last winter. locked it and left it alone. All was fine bob tailing but with a trailer EGTs are seam a little high. The security wire was still on the housing before I turned it up so I think it was at stock setting before I messed with it. I did replace the old wire lead from the guage to the probe. the old wire had the excess length coiled up and zip tied. I will buy a new wire lead from MACK and install it to see if my EGTs change. I thought someone said that the length makes a diffrence? We will see

Thanks for the info Again

[therabbittree]

your excess egt probe lead wire should be coiled up and loosly secured some where ... ie under the dash etc ..it needs to be the set length it came as to be calibrated correctly..if you secure it tightly ie ..zip tied tight to some thing, the vibration could be bad .. ie cause cracks ar shorts etc.. so just tape it or loosedly zip tie the excess..

hope this helps ya....where is your probe mounted?.. pre turbo will be more accurate and temps will be 300 degress hottter then post turbo and they will respond faster...all my probes go preturbo

thanks

Deo

[HK Trucking]

Trent, Is it getting enough air?

If you have a boost gauge what's the manifold pressure on a hard pull around 1400 rpm? If I remember correctly the 285s that I had ran about 20 - 22 lbs.

Be sure the connections on the crossover from the turbo to the intercooler are not leaking.

If the air compressor is turbocharged, check to be sure that 1" hose that runs from the intake manifold to the air compressor isn't loose or damaged, or your turbo boost can be lost there too.

Also, I had one that was losing boost pressure due to a crack in the tip turbine intercooler core.

How about the air filters? I know up here in WI, it's been real dry & dusty this summer & air filters aren't lasting long, just another possibility.

Herb

[Lmackattack]

therabbittree

The probe is just after the turbo in the exhaust elbo that points down towards the frame rail. Both the probe and guage were bought new in December 05. The wire that went from the probe to the guage was standard wire that would be used for lighting. I replaced it with new wire when I installed the new parts but Im thinking its not the right wire or length for the applacation. I am going to buy the factory wire from MACK when I get back home next week. hopefully the wire I used is the issue

HK

Im getting around 16 psi at full boost in summer 18 in winter. I thought 20 PSI was normal also but thats just what I heard from other people???The air compressor does have a 1" line from the intake manifold to the compressor. I dident think of that as a possible leak issue. I will check that line and check the charge core for leaks. My Air filters were replaced last summer and I have low milage on the truck sience I replaced them.

good ideas

thanks again

Trent

[Rob]

Trent, you need type "K" thermocouple wire for this application. A thermocouple makes it's own current to drive the pyrometer. The meter is a standard 1 milliampre full scale deflection guage calibrated to read temperature. The probe is made of two dissimilar metals that generate a DC current proportional to it's temperature exposure. Type "K" thermocouple wiring is a red wire, and a yellow wire. It is readily available from McMaster-Carr in your neck of the woods. The length is not important as it is a series connection and only has to reach your point to point mountings. The kits you purchase are generic to fit most any vehicle and too much wire is not detrimental to usage.

Rob

[Lmackattack]

Good info rob, Thanks again for the help

I found the "K" wire online. I will order it when I get home if its to pricy from the dealer.

Trent

[mudslut28]

LOL This is gonna sound crazy but I dont even use a pyrometer on my old 2 valve 300 (285?). Pump is turned waaaaay up on it...will in fact turn the manifold and turbo orange on a hard pull. However it has been like this for the 9 years I have had it so I dont even worry about it. Exhaust temp doesnt seem to be as important to a Mack motor as it is the lesser makes. This is hauling 35-45 tons of coal on 5-15 degree grades so I would imagine you wont stress a motor much more than that.

Truck has a 6 speed so the motor/tranny should be about the same as yours.

[b61mack]

LOL This is gonna sound crazy but I dont even use a pyrometer on my old 2 valve 300 (285?). Pump is turned waaaaay up on it...will in fact turn the manifold and turbo orange on a hard pull. However it has been like this for the 9 years I have had it so I dont even worry about it. Exhaust temp doesnt seem to be as important to a Mack motor as it is the lesser makes. This is hauling 35-45 tons of coal on 5-15 degree grades so I would imagine you wont stress a motor much more than that.

Truck has a 6 speed so the motor/tranny should be about the same as yours.

Those old 2 valve 237-300s are damn good engines, they pull there guts out and still keep running,i dout if there is a engine out there that small that is working as hard as they are, my 285 has been running high EGT for about 4 years still runs good and dosent use oil. Ron

[Lmackattack]

Update:

This week I installed a factory wire lead from the EGT probe in the Exhaust pipe to the EGT guage. Temps are still high under load. I checked the crossover pipe and all the rubber clamps, no signs of boost leaks. I was only getting 14 psi of boost so Today I Replaced all the exhaust manafold gaskets, studs etc... to make shure no exhaust leaks. my boost guage is now reading 15psi on a hard pull and temps are still high. this past winter when I took put the boost guage in I was getting 18 psi but I figure that was from cold temps?

I asked my local mack dealer what boost psi I should see and HK you were correct 18-22 depending on the condition/ age of the motor.

This motor uses no oil and when I had the manafold off there were only 2 cyls that has a very, very slight trace of oil seaping past from a valve or something. It did not look like a caked mess that some old engines have. all looked normal to me. Im thinking that this low boost is possible cause for the hight EGT.

I was thinking about swaping a diffrent 285 turbo on to see if it makes more boost. my turbo has a few hair like cracks in the snal but no exhause leakage from them???

only thing I can think of now is the charge air cooler is leaking? does the air that goes thru the tip turbine make its was back to the intake manafold or does it blow out to the out side air? I cant hear any air escaping??

Thanks for the help

Trent

[HK Trucking]

Hey, Trent, Looks like you've kinda narrowed it down to low boost pressure as a cause of the high EGT.

There is a gasket where the intercooler core fits into the bottom of that housing, & theres a gasket on the top of the core where the lid bolts on, any sort of less than perfect seal in these areas can lose boost pressure. A couple times when installing an intercooler core in one of those, I have run a LIGHT bead of silicone gasket sealer around those gaskets, just to be sure. (This will really make it a bear to disassemble next time though). And, as I mentioned before, I had one with a crack in the flange on top, extending into the pressurized area, allowing a small leak. It doesn't take much of a boost leak to raise the EGT.

Also, where that approximately 1 inch hose runs from the turbo crossover pipe into the tip turbine, theres a spring loaded check valve that opens when a certain boost pressure is reached, thereby allowing pressure to enter the tip turbine, causing it to "spool up" drawing air from the separate air filter element, & blowing it thru the intercooler core. You can tell when that check valve opens up because thats when you hear the sudden whistle of the tip turbine fan winding up. The actual reason for that check valve is so that in conditions of no boost, unfiltered air is not pulled back thru the tip turbine & into the engine. The boost air that is used to operate the tip turbine is exhausted to the atmosphere after going thru the tip turbine & is not put back into the engine. You're right about boost pressure being higher in the cold weather compared to hot weather,that's due to hot air being less dense than cold air. What about that line running to the air compressor?

Let me know what you find, now I'm curious about this too.

Herb

[maxidyne237]

A little off topic but i remember as a kid seeing an old f model pulling a flat bed loaded with steel ( you know he was 80,000) pass us at night uphill (5 mile hill on rt 380) like we were standing still (and we were in a car) when my father and i saw this in amazement we went and caught up to this bad f model to see under the cab the exhaust manifold and turbocharger glowing red.

My dad tells a story of a guy that used to haul oil to a black top plant at night with a b-61 and he had the juice turned up enough that supposedly he would blow a small flame out the straight pipe. He would always burn through the exhaust elbows because of the heat. Just thought id add these two little stories

[Lmackattack]

2nd Update:

I did a "sniff" test today. With the truck running I sprayed either around the charge core to see if it was sucking air..i.e leaking. no change in engine speed or sound. I also sprayed it in the tip turbine fan to see if it was leaking on the inside of the core aera. no change in engine sound. I removed the turbine fan to inspect the core. it looks clean but lightly sprayed it down with water to see if any dirt came thru. all looked clean.

with the turbine fan removed. I plugged the turbine feed pipe hole with a cap and took the truck around the block to see if I could get more boost. With no boosted air being able to bleed off to through the turbine fan pipe. i was able to get 16 psi of boost when I held my foot on the brake to give the engine a load. EGT temps were obviously rising very fast with out the turbine fan installed, so I only did a few test trials.

I still cant hit full boost or close to factory spec boost. It did however make the boost a little faster than with the fan installed so it leads me to belive that there is a large air leak that I have not found or that the turbo is worn out?

Im leaning towards the turbo fins are worn out and not allowing it to make factory boost levels?

I should have a spare 285 turbo tomorrow to test my thoughts.

What do you think?

on a side note the check valve on the fan inlet had a rubber flap that was a little worn as well. it was more or less contoured to the metal bridge that regulates how far the flap can open. I will be replacing that flap if its still availible at Mack just to elimanate that as a problem.

Thanks for the help guys.

[Lmackattack]

fixed

I pulled the turbo off the manafold and found the intire center separtor wall of the exhaust snail was deteriorated and missing!!. I could clearly see the back of the turbine blades LOL. i think that would explain the issue with low boost .

I put the "new used" turbo on and I can now get 15 psi at 1100RPM and a full 25 psi at 1900RPM She pulls like never before and EGT temps are very low at cruise.

this was fun but glad its over..

Trent

[HK Trucking]

[Lmackattack]

here are the pics of the internal destruction. its hard to see but the "tear" goes all the way to the turbine blade aera and bypassed most of the snail housing.

Enjoy

[mudslut28]

Niceee!! Yikes!! LOL Glad ya got it fixed.