EGT Probe alternate locations

[lcattin]

I have a 1999 dodge 3500 1 ton cummins.  I would like to add an EGT gauge.  The problem is that at one time the exhaust manifold cracked.  The PO had it welded ( it apprears they did a good job).  The weld is right through the center of where the recommended spot is to drill and tap for the probe. Is there an alternate location where the probe could be located?  I really don't know if I want to take the chance of drilling where the crack was.

 

[Yankneck696]

You can put it in the 123 collector & just remember that it'll run cooler temps on the gauge. How much cooler, I do not know.

 

Ed

[dorkweed]

My guess is that he/previous owner may have welded up a previous hole where an EGT probe was tapped into the manifold.  Maybe in hope to fool prospective buying that the truck was BOMBED.  Just saying, not arguing.

[lcattin]

No. I had the manifold off a while back to replace the gaskets and it had definitely cracked almost all the way round. 

[Mopar1973Man]

You can put it in the 123 side or just move all the way up against turbo on the 456 port. If its truly welded up properly that should all be one piece of metal once again so it should be good to drill and tap again. Another idea is to just replace the manifold but they are not cheap.

[AH64ID]

I'd drill it where you want it. The photo doesn't show a weld right in the drill spot, and if you hit the edge of the weld it shouldn't be a big deal assuming a good weld.

 

The weld does look good thou, as there is no exhaust leak. Exhaust components are very difficult to get a good weld on since the soot permeates and doesn't allow for a proper bead.

[lcattin]

Thanks for all the comments.  I really want to put it in the right spot.  I may be pulling my wife's 35' to Florida soon and would feel more in control if I can monitor the EGT's and boost.

[Yankneck696]

Usually, weld material is much harder than the host metal & difficult to drill & tap. The heating of the surrounding metal also may have changed the properties of the manifold & it too may have hardened.

 

Ed

[lcattin]

I took the plunge and got a set of Isspro Gauges - Mechanical Fuel pressure with an isolater - Mechanical Boost and EGT.

 

I am partially through the installation.

 

I was able to drill and tap the exhaust manifold just next to the weld and it worked like a charm.

 

Now to finish the install tomorrow.

[Yankneck696]

Glad it went in. It means that they did the weld properly & you should not have to worry about it.

 

Ed

[AH64ID]

Good deal! Be glad you went for it instead of post or a different spot.

I did my first tow 2 days ago with a pre and post turbo pyro. Wow, I always knew pre was better on a modified engine but wow! The temp difference varied based on boost, load, and duration. The pre would heat up instantly with fuel and the post takes a while. Below 10 psi there was often only a 150° difference, but going from a low to high load could see 400° for half of a hill.

I would say post is good in marine applications, but not so much in pickups or OTR rigs. It also surpised me how much hotter the post is at idle with the turbine wheel leeching heat slower than the exhaust manifold.

[Russ Roth]

I would say post is good in marine applications, but not so much in pickups or OTR rigs. It also surpised me how much hotter the post is at idle with the turbine wheel leeching heat slower than the exhaust manifold.

 

 

I have been around class 8 trucks most of my life and while driving was not my career I have done it part time since I was a teen and full time for about 4 years in my early 20's.  Virtually EVERY class 8 rig I have been around (lots of them) for at least the last 25 years have a pyro that is post turbo and if not it is drilled for the probe post turbo and plugged instead.  And those are Cat, Cummins and Mack engines.  Don't remember on the series 60's.  I also read an article by Cummins addressing the placement.  Their tests indicated a solid 300* difference post and pre.  This would have been stock engines but you have to think about why the factory would now put virtually all the probes that I have seen in the post position.  And yes I know of more than one probe over the years killing an engine when before the turbo.  Take it for what it's worth.

[AH64ID]

Yeah that's the same stuff I have seen, I am just not sure it's as good as they indicate. I never saw a 300° difference under sustained load, but have a slightly looser turbine housing than many OEM turbos in recent history.

I am guessing OEMs are more interested in ease of placement and random probe failure than anything else.

My Jacobs exhaust brake came tapped and plugged, which is where my new post is installed.

[dorkweed]

Thanks for the info John and Russ!!

[AH64ID]

I did another 420 miles towing yesterday, and it was WINDY. I'll be lucky to have broken 10mpgs.

 

I still never saw anywhere near a 300° difference, the biggest was about 240° and only for a few seconds. It seem's that 225° was about as big as it would get, but 200° was closer to the max.

[Ilikeoldfords]

I wonder what the difference would be on another truck that is not tuned quite as well as yours John. Say, a truck that has a bit to much fuel, or even not enough fuel. Just curious. I even wonder what a totally stock truck would run pre and post...

[AH64ID]

I think that the difference has more to do with the turbine housing than anything, and I would expect a bigger drop with a tighter housing as the pressure decrease is greater. I run so little drive pressure that there isn't as much pressure drop across the turbine, and thus not as much of a temp drop from the expanding gasses. By the time you get the heat to the pre-probe the tuning is out of the equation, IMHO.

 

It's hard to say thou. The QSB 480, Marine 480hp 5.9L, has a difference of 375° at rated rpm and hp. 480 @ 3400 and if memory serves it's a HX55 on that engine. The HX55 has a water cooled turbine housing thou, so I would expect a bigger drop.

[lcattin]

Well all the gauges are installed and are working great.  I immediately had to bump the regulator on the FRRP to get it where it wouldn't drop drastically under WOT. 

With the gauges installed we were ready to make the 3 hour drive today to hook up the 35' Travel trailer and tow it to our home here.  Well it didn't happen as planned.  On the way running 65mph my left front tire just exploded and had me heading toward an oncoming semi.  With some fishtailing and the Hand of God the truck was gotten under control enough to get to the side of the road and stopped so I could clean my shorts and get the spare put on.  It ripped out my plastic inner fender liner and ruined all the plastic on the front bumper which I had to rip off so I could attempt to drive once again. After finally getting to our destination I immediately headed to the local DT for a complete new set or rubber.  Now I think I may have to get another alignment also. After all that I was not up to towing a 35' trailer so we drove home and the new tires did fine.

 

What a day!!