Engine won't stay at operating temp

[EJ22T SS]

Thought I was out of the woods.

Searched archive haven't seen this one.

Just got done with swap/rebuild.

Problem: When I drive DOWN 6 mile long hill engine temp and heater temp drop off to COLD condition, like half of operating temp. Before descending hill engine at operating temp. Car is turning 3,000 RPMs in 5th gear all way down on compression/not touching gas or brake pedal. Get to bottom car is cold.

Drive up same 6 mile long hill engine stays at operating temp.

I've burped it for the last five days.
I'm on my second thermostat. A OEM Subaru one.
I boiled both to make sure they open.
This one opened at 192 degrees.
I've jacked up drivers side overnight cap off.
Opened bleeder cap on radiator multiple times
I've parked on a 17 percent grade/hill at operating temp heater on.

Replaced during swap/rebuild:
Water pump.
All new hoses, even the little ones, and the heater hoses too.
I've wiggled and squeezed them all.
New over sized aluminum radiator.
New radiator cap - 13 pound.

I've checked the heater hoses to make sure I didn't reverse them.

No Check Engine Light.

So what am I missing? More trapped air?
Thermostat opens fans come on.

Can you really have too big of a radiator? Thermostat has got to closing or engine wouldn't ever get to operating temp.

Suggestions or a better yet a solution please. Before I pop a head off.

Thanks in advance.

[mike-tracy]

I had something similar, and it was the gauge temperature sensor, not the ecu one. Car was running normally, just the gauge would go up and down. Brand new one fixed the "problem"

[EJ22T SS]

I believe the gauge to be accurate.

I don't have any heat at bottom of hill either.

[IronMonkeyL255]

Well, coasting for 6 miles, you aren't generating any heat so this makes sense. 6 miles is a pretty damn long way to coast, plus since it is running on compression, it is cycling cool air through and not injecting any fuel. All this adds up to 'gonna cool shit down'

Is the car fully warmed up when starting down the hill (been running for a bit at operating temp on the gauge, not just hit it). If it's clear enough, try leaving it out of gear and just idling to see if it does the same thing.

[Alphius]

6 miles of constant compression braking? How long does this take to drive down? Its definitely not out of the question that it may just be cooling off enough to reduce heat output in that amount of time. These cars do have Decel Fuel Cut which means that anytime you are engine braking and the tach is over 1500 or so the ECU is not injecting any fuel and no combustion is happening.

Edit: Ninja'd by IronMonkey!

[EJ22T SS]

Thanks for your reply's.

Driven down 6 mile long hill in same fashion for 25 years of commuting in NA 2.2 Legacy. No issues.

Leave in 5th don't have to ride brakes for next 6 minutes to keep speed in check for the Idaho State Police running radar each day on their favorite speed trap.

New 1993 turbo not like so much.

Engine has plenty of time to come to full temp before decent of hill. Cold as can be at bottom.

Options to test:

Just coast.
Put in fourth and push on gas to make go at speed/60 mph
Leave in 5th run the gantlet of Radar.
Just go to recycle bin and put cardboard in grill for winter?

I can see the sheer volume of air passing through engine could be cooling it off. It is also not something your going to experience in Nebraska, Floria.

How hard on engine? Slow cool off over 6 minutes. Burns more fuel having to heat back up. Two extra heat cycles for no go reason?

I'll keep you posted. Going to be Wednesday before I go down it again.

[IronMonkeyL255]

I take it the the N/A was a 5-speed as well?

It may just be that the turbo has a more robust cooling system that the n/a you are used to.

This is an interesting occurrence. I often try to coast down as many hills as I can to try to save a little gas, but hadn't ever thought about it cooling down until you mentioned this.

[EJ22T SS]

In last 25 years:

425,000 in 1992 Legacy Wagon-RIP
100,000 in 1992 Wagon - lifted
341,000 in 1997 Outback Wagon

All five speeds.

Drive to top of same hill leave in 5th gear "coast" or be on compression till bottom of 6 mile hill at 3,000 rpm or so at 60 mph. No problem or drop off in temp in NA engines.

Now new to me 1993 Turbo with new 5MT speed swap and Cat-less down-pipe.

Larger cooling system in turbo, and now larger radiator, plus lower compression engine ,with turbo pulling way more air on or off turbo, sucking through engine with little back pressure and cat could be the problem.

The added "turbo effect" or added volume of air and cooling over six miles might be it.

It is the only time I see the temperature gauge drop.

So I'm going to try 4th gear and "push" car down hill. See if that fixes it. Simple fix. If it works.

I'll know more next time I drive down in 4rth gear.

It is way more fun driving up hill in a turbo after 25 years of N/A.

[James614]

I'd go ahead and try the cardboard and see what difference it makes.

[Legacy777]

Bottom line, the engine should maintain proper coolant temperature, regardless whether you are coasting for 6 miles or not. Where does the engine temp gauge needle show at normal operating temp and where does it show when you've reached the bottom of the hill?

As you descend the hill and you have the heat on does the heat gradually reduce or is it more of a sudden decrease in temperature?

What modifications does your engine/car have?

[EJ22T SS]

Have 8-10 minute drive at 65 MPH before descending hill.

Engine temp just a tick above half on gauge at top of hill. Slow loss of temperature, at bottom of hill temp gauge less than 1/4 up. Hand testing "heat" coming out of vent cold to touch.

In the past I've found the heaters in the Gen 1 Legacy's to just about cook me if I leave them on high and fan set to 4.

1993 Stock engine 1991 heads
Stock turbo.
Stock intake and air cleaner box.
50/50 mix on anti-freeze

Mods:

Catless down pipe
Aftermarket Komo aluminum radiator.
Heat tape wrap on stock header.
Subaru oil cooler from 1991
4EAT removed replaced with 5MT

No Check Engine Light

Thanks for you help.

[Legacy777]

Hmmm

Is the engine temp always a tick above half when driving around town or during "normal" driving?

I ask this because I've driven across country several times and climbed the continental divide and didn't take it easy on the car and the temp gauge has never moved. It's always stayed just a slight tick below middle. And yes the heaters in these cars will cook the crap out of you.

The fact that you may be seeing slightly higher temperatures when climbing a grade, even with an oversized radiator seems odd to me.

Can you go into any additional details as to the work you did, what parts were used, what were new and were they aftermarket or Subaru? Are you 100% sure you have all the coolant lines hooked up properly?

Are you having to add any coolant to the system?

[Someperson]

all my leggies have stayed a tick above half as well in all conditions, DD a 94 NA atm, just my .02

[EJ22T SS]

Engine temp is exactly where have seen last 800,00 miles in N/A 5 speed Subaru when warmed up. Ever so slightly above half being a tick. Just noticeably barely above half. Doesn't move unless descending hill.

Only time I've seen a gauge move before, on that hill is "UP" at 100- 105 degrees ambient temp/summer pulling 18 foot outboard jet boat behind N/A 2.2 Legacy. Yes! No flipping kidding. Did it and multiple times, and still do. Third gear 3500 RPM's. Flipping amazing engine and HP torque to pull hill and boat off of ramp, with Borla header as only mod. My 1997 Outabck won't do it even with same header. I hate that 2.5 Outback, even though I have driven it over 300.000 miles. No comparison when it comes to a 2.2 versus 2.5. I'd take a 2.2 every time, better engine.

This is why the, What The Heck? Really, on decent moment?

Burped this 1993 turbo car over and over when filling with coolant. Been sitting 3 days with radiator cap off. Now no need to add fluid.

What part of "cool" doesn't "turbo" dictate for longevity? Both oil and H20? A thermostat should take care of engine temp even if an swimming pool is behind it. Shut down to just a trickle or off.

NAPA H2O pump is biggest after market part. Spent big bucks buying Subaru OEM hoses to replace 20 yr-old crusty crap. NAPA upper and lower radiator hoses.

As far as hoses and mixed up lines it is possible but unlikely as "OEM stock lines tend to lead you to stock holes.

I don't doubt I'm more stock than most of you here.

Wonder if catless down-pipe and lack of back pressure on long decent is root of issue?

Temp on up hill doesn't change and is same as flat running or normal.

[Alphius]

If the throttle is closed the car is in decel fuel cut mode which is the exact same as having the car completely off as far as heat generation; there is no combustion occuring. If anything, it cools faster because of the cool air being drawn through the cylinders as the car rolls downhill.

If I had a hill that long and steep around here I would try it myself in my N/A Legacy vs my Turbo.

How fast does the car warm up from cold? I could see this being an issue if the thermostat was not closing all the way, allowing the warm coolant to cycle through the radiator as you travel downhill with no additional heat being generated to replace the heat lost.

[wtdash]

Found THIS THREAD that was taken from the the now defunct Revtronix site which leads me to believe your car is 'over cooling'...I don't have any answers, but thought this was relevant:

Deceleration

Conditions:

* Throttle closed
* Low engine load
* Engine speed above idle limit

Under engine deceleration, no power is necessary so fuel ratio can be leaned out and eventually the fuel injectors can be turned off completely. Spark timing is set to transfer combustion heat to the rest of the engine to slow heat loss instead of expelling it out the exhaust. Deceleration mode will eventually be disabled under prolonged deceleration to prevent the engine from cooling too much, which would require another warm-up period.

[EJ22T SS]

Thank you. For your input and reply.

So the hour I spent in garage drilling 1" holes in 1/4 plywood, creating a winter grill insert, was good time spent. I'll know Thursday am, just in time for cold snap. Over cool, oversize radiator, will be tricked to be underutilized, as it will be blocked by grid of 1 inch holes between upper radiator mounts to bottom of radiator.

I'd guess, I've cut surface area by 50% which would be in ballpark of stock.

We will see in am.

Thanks again for your help and support.

[EJ22T SS]

Well today's drive to work yielded some improvement on cold condition on decent of 6 mile long hill.

What a fickle little bugger.

No surprise engine warmed up quicker, but, didn't overheat 30 degrees outside. Held temp almost to bottom of grade.

Left in fourth gear with slight touch of foot on gas pedal to maintain speed, 3,500 rpm to maintain 60 mph.

Gotta tickle pedal to light fire to car to keep it lit and warm. Must be fuel cut. Lack of back pressure dropping from 5th to 4rth barely drops speed and creates a tap dance with gas pedal to just barely push on it to keep withing speed limit of 60 mph with gravity assist on grade.

Weird to have to watch both speed and temp gauge at same time to regulate gas pedal.

I swapped out for 3 inch bellmouth catless down-pipe with stock 2.5" exhaust behind that. New car to me and never drove car with stock down-pipe and back pressure. Anyone out there who can describe difference? Would stock down-pipe fix problem?

I have one, would wiling to go back to totally stock to avoid daily dance if it would.

I'm tickled with turbo "performance" from NA, without messing with BS of non stock if it would improve chilly-tap dance on daily drive.

[mike-tracy]

With my td04 (just a hair bigger than a stock vf11) I had worse spoolup than the stock exhaust setup. No change in engine operating temp

[kleinkid]

Mike Tracy said to replace the temp sending unit, $32, couldn't hurt to have a fresh one in there getting good data.

[cj91legss]

I have a TD04 and 3" exhaust to an STI axleback, and my spool up is.....ok... However I also have a really low compression build in my car.

I'm going to +2 the temp sending unit (since mike already suggested earlier,) It's a cheap part to rule out an inaccurate sensor and like kleinkid said, it'd be nice to have a fresh one in...

[EJ22T SS]

I'm good with spending $32.00 bucks, as it is a drop in the bucket on rebuild,/swap, to get good info. If I was cheap I'd reuse the one out of the 1991. Going to buy OEM Subie I even if it costs $64.00 just to make sure. Winter/screen with 1/4 plywood with 1" holes helps but doesn't fix problem. I want to be done.

[turbo5711]

I know what it is the engine need to be burped all know it

[EJ22T SS]

It is possible that I might still have an air bubble after daily and nightly burping for over a week.

If so, where would it be hiding? How to relive it?

In all driving conditions except long downhill car is fine.

[cj91legss]

http://www.rs25.com/forums/f190/t116363 ... ystem.html

I have one of these kits. Works AMAZING.

Of course you'll have to ignore the arguments in the discussion under the first post.