Rear heater cooling the engine coolant?

Furi · Post by **Furi** » Sat Jan 14, 2017 4:56 pm

So I recently did a temp reading of the in/out engine coolant hoses from the rear heater while in operating temperature. The in-line had a reading of 145 F, the out-line had a reading of 85 F. Mind you the rear heater was not on, not the blower, not anything. The coolant just circulated through it. Outside temperature was about 40 F. Would the rear heater cool the engine coolant that much in this scenario?
I'm in the process of removing the rear heater/AC as I won't be using it and wanted to reduce weight and make space for other things. But that difference in temp seems pretty significant.

Post by **Growlerbearnz** » Sat Jan 14, 2017 8:31 pm

Huh. That's a higher temperature drop than I would have expected. How long had the engine been running before you measured the temperature difference? Was the rear heater control set to hot (even though the fan wasn't on)?

Still, plenty of L300s were made without the rear heater (but had the same front heater and radiator), so I don't see any reason why you can't remove the rear heater. Or to look at it another way if the rear heater is all that's keeping you from overheating there's something wrong!

Furi · Post by **Furi** » Mon Jan 16, 2017 8:53 am

Engine was on for about 15 minutes with a little drive in side streets. I checked the temp by using an infrared thermometer on the hoses. I removed the heater controls from the cabin a month ago, and of course didn't pay attention to the settings :)

I was actually checking the temp of the hoses to see if any engine coolant was flowing at all since I wanted to pass the engine coolant through a heat exchanger after removing the rear heater. I also checked the temperature of the hose for the front radiator and it was about 5F degrees warmer than the in-hose into the back heater.

I haven't had any overheating issues but good point regarding the Deli's without a rear heater. I'll check the temps. after the mod. in similar scenario and see how it goes. But the difference in in/out temps. was surprising!!!

Post by **Growlerbearnz** » Mon Jan 16, 2017 1:09 pm

From memory (which means I'm likely to be wrong) the rear heater has an inline valve which shuts down the flow of coolant to a trickle when it's set to "cold" (unlike the front heater, which has full coolant flow all the time). I wonder if your rear heater is set to cold, causing it to take a very long time to warm up.

Post by **FalcoColumbarius** » Mon Jan 16, 2017 3:53 pm

When climbing really steep hills, such as the Kootenay Pass 1,775 metres (800 metres in about ten or so kliks), I find that it pays to have a working cabin heating system, as well as the cockpit heating system, when it comes to providing additional cooling for the motor.

Falco.

Furi · Post by **Furi** » Wed Jan 18, 2017 7:18 am

Would make sense for the heaters to be able to cool the engine coolant some; I've also used the heater to draw outside air in cooler days to do the same. But just didn't expect it to be that much from the back heater.

Will do another reading and compare to the temps in front radiator when the engine is hot and proper to verify.

Post by **FalcoColumbarius** » Wed Jan 18, 2017 4:37 pm

From what I understand, and as correlates to GBNZ's memory, however flawed it may be, when one turns the heat on in the cabin and turns the fan on it opens up another few feet of potential cooling system, although it does pay to have the aft windows opened when you are doing this in the Summer. That hill is steep and long. I watched my temperature climbing, turning the heat on I witnessed the needle stabilise then gradually drop a little.

Falco

Post by **thelazygreenfox** » Wed Jan 18, 2017 7:08 pm

Hi Furi, FC and GB
The rear cooling lines function as a cooler as well. I tossed all the data I collected years ago on my L300 cooling but I would be hesitant to remove the heater, knowing the overheating history of the L300 diesel, mine included.

At the very least loop the rear cooling lines so they function as they're meant to. Someday you may need the extra cooling those parts provide.

MD

Furi · Post by **Furi** » Fri Jan 20, 2017 4:27 pm

Thanks both for the feedback!!

thelazygreenfox wrote:
Hi Furi, FC and GB
The rear cooling lines function as a cooler as well. I tossed all the data I collected years ago on my L300 cooling but I would be hesitant to remove the heater, knowing the overheating history of the L300 diesel, mine included.

At the very least loop the rear cooling lines so they function as they're meant to. Someday you may need the extra cooling those parts provide.

MD

Wish you still had the numbers. But that seems to be the case based on the temp readings.

My plan was to just remove the heater and leave the piping in place and pass the in/out coolant line though a liquid/liquid heat exchanger to heat water. Wanted to save on weight and use the space for other things.

But I did another reading of temps and having second thoughts on removing the heater considering how much it cools the coolant. And thats even without the blower running.

This is after an hour of driving; no hills so temps didn't rise that much. But the readings were consistent to previous one.

Rear heater in coolant hose: 145F
Rear heater out coolant hose: 95F
Front radiator hose: 150F.

Just to make sure I have this right. These are the hoses; right?

: 20170119_123105.jpg (26.11 KiB) Viewed 7345 times

Post by **Growlerbearnz** » Fri Jan 20, 2017 10:40 pm

Yup, that's them. I'm still surprised at the temperature difference without the fan on!

Furi · Post by **Furi** » Sun Jan 22, 2017 1:30 pm

Growlerbearnz wrote:Yup, that's them. I'm still surprised at the temperature difference without the fan on!

So was I!! Could someone with a rear heater do a quick reading on the hoses to verify this? Good info to have.

Post by **Growlerbearnz** » Sun Jan 22, 2017 5:14 pm

I just measured mine. This is on a 23C day after a half hour drive, measured with an IR thermometer on the steel lines, engine idling, rear heater set to cold: 77C in, 79C out. Radiator top tank 92C.

There's probably a little more difference than I measured, as the IR thermometer's aperture is a bit bigger than the steel lines' diameter- it's likely measuring a bit of the background as well.

Furi · Post by **Furi** » Mon Jan 23, 2017 1:32 pm

Ok. So I'm putting up my heater with its incredible cooling capacity up for sale for 1 million dollars. The formula derived from the magic dust inside is probably worth much more but I need the money.

But before I do that, when you get a chance could you check the temps again with the back heater set to heat without having the blower on? Wondering if you at least get readings that are closer to the front. I actually got pretty inconsistent reads on the metal pipes and checked the checked the temps of the hoses.

Post by **Growlerbearnz** » Tue Jan 24, 2017 2:09 am

Errrr... I'll try, but don't hold your breath- it's been a stinker of a summer so far and I need all the aircon I can get.

Furi · Post by **Furi** » Tue Jan 24, 2017 10:45 am

Maxing the aircon in January; must be nice :) No worries.

Did another reading with same results as before; still no good explanation for the big temp difference!