OPS relay mod

[drocker]

New here and this is my first post. I currently have a 1994 GMC Yukon that I recently picked up.

I have searched and read many post about the OPS, LP and the relay mod. I am pretty sure how to begin this task but I do have a few questions.

If you look at the 2nd picture you will see how I plan to wire up the relay to the lift pump. Where I get confused is in the 3rd picture. What is this LP relay shown here for (had to borrow the pict) and will my relay mod hook up before or after this relay. I was planning on cutting the wires to OPS about 3 to 6 inches back from the plug to the OPS.

One other question I have is with the thermostat. Some say 180 is better than the 195. Some say the fuel mileage will be hurt using the 180. I am reading so many different stories. I am running the 180 stat and before I switched it from the 195 my truck ran just fine before. Now I changed it about a week after I got the SUV and my current mileage is around 14.5 mpg. This seams pretty low since I don't tow but some say it could be cause of the winter diesel. Any ideas why it could be so low?

Thanks.

Thanks.

 

[Chevylover]

I'm happy with my 180°F thermostat. Never I'll go back to the standard 195°F. With this my engine will get to hot while towing 5 tons. With the 180, the temp stays at 185° on the temp gauge.

But that's just my 2 cents.


Cu,
Sven

 

[Pruittx2]

well first off Welcome to the site! Next when you get a minute,, go up and look for the USECP link in the site hearder, to fill out a Signature, to show us all the options your your nice Yukon, RPO codes are on a sticker on the glove box, you could look up to see what gears you got, and other usefull stuff. A few diff factors will get your mileage down, But do tell if you have done any Mod's like air box mod, downpipe, and such.

some else will chime in on the relay info,, as I have been thinking of doing this to mine also, just ain't got the time right now.

Again,,,,:welcome8: and :welcome3:

 

[drocker]

Updated signature. Not sure what gears yet. I know with the 285/75/16 tires I am running right at 2000 RPMs at 65 mph. Photos below show my custom CAI and ground mod to stop the gauges from bouncing.

 

[ak diesel driver]

Can't help with the relay. FYI your cai is not a cai just free flowing. It's sucking hot under hood air. I think your mileage is low because of your tire size and #1 fuel doesn't help either.

 

[drocker]

^ Sorry but I use the CAI pretty loosely in terms when talking about this type of setup. Also I dont see how my tire size can effect fuel mileage that much. I know they are one size above stock but running a smaller tire would mean more RPMs when doing the the same speed. Of course running to tall of a tire will mean more fuel for get up and go. I guess I will wait until spring or summer to see what my mileage turns out to be.

 

[vail426]

The third picture is the factory relay I believe. I'm not familiar with the 94 set up. If i am correct, leave that relay be and fashion your own relay in to reduce the load on the OPS according to your diagram.

 

[drocker]

^ thanks.

 

[matuva]

good reading here : http://www.thetruckstop.us/forum/showthread.php?t=4464&highlight=relay

 

[drocker]

^ Thanks. I think I read the thread a thousand times before I felt comfortable about doing the mod. Then I saw the relay picture for LP on the firewall which is like my Yukon. So then I got confused again.

 

[JiFaire]

Welcome to the site, drocker.

My opinion on your thermostat is a bit different than Sven's... actually, a LOT different than Sven's. Make of it what you wish.

Putting in a 180* thermostat won't help keep you cool when towing, other than starting the floor a bit lower. The thermostat sets the bottom temperature, not the top one.

Not sure what you know, so bear with me:

FIRST OFF: if you replaced your thermostat with anything but a genuine ACDelco thermostat, the PROPER one for your truck, there's your problem. You have a 1994 1Tstat system, and you need the right thermostat... Stant won't work right. Neither will NAPA, Autozone, Harbour Freight, Walmart, or one from a gasser. (The proper Stewart thermostat will work, also. Just don't expect to get a cheap one and be happy) These things like to run hot, and will get your best fuel economy around 195-200*.. 180* is too cool, IMHO.

- when the engine is coming up to temp (below 180*), your thermostat stays closed. Once things hit 180*, it opens to allow coolant flow and circulation through the rad, where cooling happens.

- A 195* thermostat does the same thing, only at 195*. Now... when you're towing, your engine is probably at operating temp, meaning the thermostat is wideopen. From this point forward, the thermostat might as well not be there... it's wide open, right?

If your rad cannot eject heat fast enough, and your engine continues to add heat, you will overheat. Period. With either thermostat. Every time.

That means if you're pulling 9800# high-front 5th wheel, into a hot wind, in traffic, in Southern Utah, and your IATs keep climbing, and your EGTs keep climbing, and your tranny unlocks and you end up running in 2nd or 3rd, you are screwed. Ask me how I know this.

Your truck has only a single thermostat, so there are some critical things you need to do:

- pull rad and clean it. Many times. Takes 3-4 hrs to do it right.
- replace thermostat with genuine ACDelco thermostat. Make sure it's the right one for your truck. Use no substitutes!
- check your fan clutch to make sure it kicks in properly and at the right temp. If not, either replace it or modify it to work right.
- do the TCC lock mod.
- Minimum3" exhaust, definitely replace your 1994 frankenstein downpipe with a 3" mandrel-bent one. I mean that.
- Turbomaster and GL4 chip.

Voila... no overheating with big load.

Now.. about your mileage. You are in Kansas. It's December. In your ambients, I bet the truck isn't warming up with that 180* thermostat; between that and #1 winter fuel, yeah, it'll cost you 5-7 mpg..

I suggest going back to the proper 195* thermostat, but at the very least, Put cardboard over your grille for a tankful and see what happens to your mileage.


Again, welcome to the best 6.5TD place on the net! Hang out with the guys... we'll get you running fine!

 

[Pruittx2]

Yeah.. What he said" :iagree: :welcome8:

 

[drocker]

JiFaire, current t stat is one from autozone. I know for sure it is a stant brand. I will purchasing a ACdelco from one of the online dealers that is a 195 stat to replace the current. It wasn't overheating before but the 195 stat that I replaced looked just like the stant one. I will never probably tow anything with this vehicle. I have seen the ACdelco and they do look a little different. The link below shows the one I will probably get but it list it as a 190 t stat. Part # listed is ACDELCO Part # 13191. So is this right?

http://www.rockauto.com/catalog/moreinfo.php?pk=79801

 

[Woody35]

btw 285/75/16 are not 1 tire size above stock its two, and on some trucks its almost 3 that came with 235s.

 

[drocker]

^ sticker on driver side door panel has tire size as 265/75/16. My 1994 fullsize chevy blazer (350 gas) that I sold had 265/75/16 which was shown on door panel as well.

 

[Woody35]

^ sticker on driver side door panel has tire size as 265/75/16. My 1994 fullsize chevy blazer (350 gas) that I sold had 265/75/16 which was shown on door panel as well.

sorry i am mistaken then. well my truck came with 245s. thought it was universal

 

[WarWagon]

Not to tangle with the admin, but to clear a point up:
The 180 T-stat starts to open at 180.
The 195 starts to open at 195.
It is accepted that the t-stats are full open 10 degrees after their set point.

So a 195 gets you 205 ECT at the outlet before it is full open. This gives you a narrow 10 degrees to get the fan on and avoid going over the 215 head cracking temperature. The harder you 'suddenly' load the engine the higher the temp overshoot can be before the fan kicks on. So there is an advantage for a lower t-stat if you tow and work it hard. But disadvantages are shown above.

I will second the advice of pulling the oil cooler and cleaning the mat of debris behind it.

I like the link with the separate lift pump relay. Do not use the factory crank fuel pump relay for this... But you can use one exactally like it and they leave you space for it too most times.

 

[JiFaire]

Good point on the relay, WW... and don't worry about 'tangling with the admin'... we all share info here - some of it conflicts, some of it agrees, some of it builds on the others... that's how we learn. All of us, me included!

At the end of the day, we collectively get damn good information that has been vetted through many smart guys - which makes this the best place to build your 6.5 knowledge. If this ever turns into the kind of place where those exchanges aren't encouraged, and where people don't work together, then you're on the wrong site.

Back on track - I put my Stant (yeah, I did it, too - once) 195* thermostat in a pot of water and boiled it, after Bill Heath suggested it when we changed it out for the ACDelco 195. The damn thing started late and only half-way opened by the time it was at 205 on my IR thermometer, and never opened much more than that by 212... I dunno HOW hot you would have to get it to open fully.

I've done the same thing with a few of the ACDelco 195s and they were wide-open before 200. I never install a thermostat that I haven't checked, since that experience.

 

[vail426]

Non Delco stats tend to have wide temperature swings.

 

[Green Machine]

I would still take a 195* over a 180*. 195 I consider the best operating temperature for these engines... 180* is to cool and probably makes the engine less efficient, but that's my theory...

And about tire size... I don't really see tire size effecting actual mileage much, but there are a couple reasons bigger tires may calculate less mileage...
1.) Speedo calibrated? If not you are reading less mileage on your odometer too because you are going more miles with less turns of the tire.
2.) Tire tread... the pattern and overall design of your tire can effect mileage... When I went from BFG A/Ts to Yoko M/Ts I lost ~1-2 mpg.