HELP! Engine running too cool

t0rquey · **Posted:** Mon Feb 22, 2016 10:40 pm

I have the OEM stat and no mech fan. When cruising down the freeway, the temp sits right at 168°. In 20° weather the other day, I idled for fifteen minutes with the heat on (AC and e-fan cycling) and saw the temp slowly climb to 194°. Within a half-mile of driving down a 45mph road, the temp was back down to 168°. This was all according to Torque Pro and my ELM327.

thermorex · **Posted:** Mon Feb 22, 2016 10:47 pm

geordi wrote:

I disagree that the cooler a transmission is, that it contributes to lower MPG. Modern synthetic fluids are designed to be stable and operate consistently across a wide range of temperatures, none have ever stated there is a problem with operating too cold or below a certain threshold. Too hot on the other hand.... The temps that you say your transmission is running are perfectly acceptable. The transmission in my TDI has an external cooler as well, and runs about 100 degrees over ambient pretty much all the time except in stop-and-go traffic. Heat is primarily generated from an unlocked torque converter, so whenever you are on the highway, the converter shouldn't be slipping and you also aren't changing gears much, so the transmission is effectively straight through. This is why it isn't generating as much heat either, so there isn't as much of a penalty for fluid that might be too cold.

But the normal operating range of transmission fluid is between 130 and 190 anyway. When you start climbing above 200, the lifespan of the fluid drops off precipitously because breakdown happens very quickly. If your fluid climbs past 230, you should consider replacing it very soon. If it hits 250, the fluid is done immediately.

My transmission runs about 160-170 on the highway, cooler when the ambient temps are cooler... It was running about 130 when driving around NJ a few weeks ago. My mileage has been rock-steady at 36mpg per tank for many months, and that is at a highway speed of 83mph! This is on a 2003 VW TDI wagon with the automatic transmission, so this mileage is pretty much spot-on for the higher-end of the range it is capable of.

I'd always prefer the other fluids be too cool rather than too hot. It's easy to make things hot. Keeping them cool is hard.

There are subtle gains when running a transmission warmer, but within safe intervals. The modern hydraulic oils still gets thinner at higher temperature. And, as an extra argument, ram has a transmission warmer on the zf transmission, which earned them some carbon credits since it improves the mileage. This can be researched online. This being said, I still like to run transmission on up to 160F. Ram runs 185-195 all the time and I don't like it. It's a project for me to find ways to drop it, but things are overly complicated due to the transmission warmer with a build in bypass valve and coolant going through it. The warmer is installed over the transmission, similar to the crd oil cooler.

flash7210 · **Posted:** Mon Feb 22, 2016 11:01 pm

t0rquey wrote:

I have the OEM stat and no mech fan. When cruising down the freeway, the temp sits right at 168°. In 20° weather the other day, I idled for fifteen minutes with the heat on (AC and e-fan cycling) and saw the temp slowly climb to 194°. Within a half-mile of driving down a 45mph road, the temp was back down to 168°. This was all according to Torque Pro and my ELM327.

Interesting.
Last week, 40 F morning, driving to work, heat on and AC off.
Drove 5 miles and got up to 175 F when when I pulled into the McDonalds drive thru.
Idled for about 5 min while moving through the drive thru.
Temperature dropped to 168 F.

I'm using a modified (gutted) OEM thermostat housing with a 195 thermostat in the upper rad hose.

geordi · **Posted:** Mon Feb 22, 2016 11:35 pm

thermorex wrote:

There are subtle gains when running a transmission warmer, but within safe intervals. The modern hydraulic oils still gets thinner at higher temperature. And, as an extra argument, ram has a transmission warmer on the zf transmission, which earned them some carbon credits since it improves the mileage. This can be researched online. This being said, I still like to run transmission on up to 160F. Ram runs 185-195 all the time and I don't like it. It's a project for me to find ways to drop it, but things are overly complicated due to the transmission warmer with a build in bypass valve and coolant going through it. The warmer is installed over the transmission, similar to the crd oil cooler.

Unless there is some sensor nanny system going on, it seems like that "warmer" system would be pretty easy to delete by just looping the coolant lines together. There IS an actual transmission cooler somewhere, right? If not, then that isn't a "warmer" it is the only heat exchanger, and the idea is to regulate the transmission's temp at the same as the engine coolant. The problem is that transmissions will want to run HOTTER than that, b/c they will be adding heat to any temperature they are given to start with - usually b/c the exchanger isn't anywhere near large enough.

You may want to look into something like a Derale transmission cooler - look up the 13900 model, that is a pretty nice one with its own fan. The thermostat is garbage, but everything else is great.

flash7210 · **Posted:** Tue Feb 23, 2016 6:38 am

Quote:

I disagree that the cooler a transmission is, that it contributes to lower MPG.

What about those cold mornings where the transmission hasn't warmed up enough and wont apply the TCC? Surely that has to be hurting efficiency.

I really wish I could figure out a way to disable or fool that sensor because I find that feature really annoying.

t0rquey · **Posted:** Tue Feb 23, 2016 8:31 am

flash7210 wrote:

I'm using a modified (gutted) OEM thermostat housing with a 195 thermostat in the upper rad hose.

Do you have a mech fan?

flash7210 wrote:

I really wish I could figure out a way to disable or fool that sensor because I find that feature really annoying.

That drives me nuts as well.

flash7210 · **Posted:** Tue Feb 23, 2016 8:41 am

t0rquey wrote:

flash7210 wrote:

I'm using a modified (gutted) OEM thermostat housing with a 195 thermostat in the upper rad hose.

Do you have a mech fan?

Nope.
And currently, the way I have the electric fan wired, the fan is always on LOW. I added a toggle switch to switch between LOW and HIGH.

flash7210 · **Posted:** Tue Feb 23, 2016 11:40 am

papaindigo wrote:

Remember the primary purpose of a tstat is to bring the engine coolant up to a minimum operating temp before that coolant goes thru the radiator and a secondary purpose may be to keep coolant temp at or above the fully open temp; it is NOT to control maximum coolant temp (e.g. once a tstat is fully open it has no influence on coolant temp)

So I guess I'm asking those with the gear to read actual coolant temps direct from the ECU in XXXF what actual operating temps are they seeing with the OEM tstat, inline tstat, and turbo diesel freaks housing with either the 195 or 203F thermostat inserts?

On a related note what is the "ideal" operating temp?

I think the "ideal" operating temp depends on the operator and how/where they use the vehicle.

I use a modified (gutted) OEM t-stat housing with a 195 t-stat in the upper rad hose.
On a hot summer day here in FL, with the AC on, coolant temps can easily get up to 205. But usually they stay around 197 and I'm happy with that.

I think that folks who tow heavy loads, especially in mountainous regions, would do better with a 180 t-stat. Just so that the cooling system has some more headroom and doesn't get too hot too quickly.

I dont know if any of this applies to the CRD engine, but...
I've seen some engines, mainly large V8 gasolene engines, where the rear most cylinders run hotter than the front cylinders that are closer to the thermostat outlet.
For most operators, this isn't a problem for daily driving.
But if these engines are used in racing or heavy towing this inbalance in head cooling can lead to warpage and premature heat gasket failure.
I've seen two solutions for this issue:
1. run a cooler thermostat so that overall the heads are cooler and the temp inbalance is less drastic.
2. add coolant passages (hose or metal tubes) from ports at the rear of the heads up to the thermostat outlet so that coolant from the rear most cylinders has a quicker path out.

thermorex · **Posted:** Tue Feb 23, 2016 3:01 pm

flash7210 wrote:

Quote:

I disagree that the cooler a transmission is, that it contributes to lower MPG.

What about those cold mornings where the transmission hasn't warmed up enough and wont apply the TCC? Surely that has to be hurting efficiency.

I really wish I could figure out a way to disable or fool that sensor because I find that feature really annoying.

I think the easiest is to install a pad warmer on the transmission pan. I don't have this issues since my crd is always garaged, and when I leave in cold mornings the transmission temps are not very cold.

thermorex · **Posted:** Tue Feb 23, 2016 3:19 pm

geordi wrote:

thermorex wrote:

There are subtle gains when running a transmission warmer, but within safe intervals. The modern hydraulic oils still gets thinner at higher temperature. And, as an extra argument, ram has a transmission warmer on the zf transmission, which earned them some carbon credits since it improves the mileage. This can be researched online. This being said, I still like to run transmission on up to 160F. Ram runs 185-195 all the time and I don't like it. It's a project for me to find ways to drop it, but things are overly complicated due to the transmission warmer with a build in bypass valve and coolant going through it. The warmer is installed over the transmission, similar to the crd oil cooler.

Unless there is some sensor nanny system going on, it seems like that "warmer" system would be pretty easy to delete by just looping the coolant lines together. There IS an actual transmission cooler somewhere, right? If not, then that isn't a "warmer" it is the only heat exchanger, and the idea is to regulate the transmission's temp at the same as the engine coolant. The problem is that transmissions will want to run HOTTER than that, b/c they will be adding heat to any temperature they are given to start with - usually b/c the exchanger isn't anywhere near large enough.

You may want to look into something like a Derale transmission cooler - look up the 13900 model, that is a pretty nice one with its own fan. The thermostat is garbage, but everything else is great.

Geordi, we complain about too many sensors in crds... If you see how ram is, you'll be running back to crd for how simple it is. Ram has a transmission warmer and a transmission cooler, similar to crds, shared with the Ac heat exchanger. But the cooling management in ram involves an extra 2-1 valve that's controlled by ecm. Coolant gets through one port and the exit ports go to the cabin heater and transmission warmer. Depending on how much heat is required in the cabin, the computer tells the 2-1 electronic valve where to distribute warm coolant. Once there is no need for cabin heat, or when the engine warmed up over 150-ish degrees, the 2-1 valve starts distributing warm coolant to the transmission warmer.

I heard from gde that jeep EcoDiesel does not have the transmission warmer. Go figure, you'd expect to be the other way since you're more likely to tow with the ram. Anyways, the advice from gde is to bypass the coolant from the transmission warmer. Going this route will probably let the transmission to operate few degrees lower, as the coolant won't heat it. The disadvantage would me no transmission heat in the cold winter days. But there is still the problem of the bypass that's in the transmission warmer, which won't let the transmission fluid to go towards the cooler unless it passes a specific temperature, which I don't know right now what that value is, but I suspect it opens at about 170-ish. There are people in the ram forum posting pics with their transmission temperature at 230F, while towing in the summer. That is too hot by any standard.

My plan is to take that transmission warmer out, see what I can do about the bypass valve, maybe take it out if possible and let the coolant flow through the warmer as before. If still the transmission temperatures are high, then I can add a manual valve operated by cable (similar to manual heater valves available in generic Autoparts stores) to restrict the coolant flow through the warmer in demand, this for hot summer days. Anyways, it's not as easy as it would be on the crd. So far this is my only significant complain regarding the ram EcoDiesel.

HELP! Engine running too cool

Who is online