Overheating with temp gauge at 1/2? - MR2 Owners Club Message Board
Reply
 
LinkBack Thread Tools
post #1 of 22 (permalink) Old June 9th, 2019, 14:18 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Overheating with temp gauge at 1/2?

Hi Folks,
I've got a '92 JDM Gen II turbo, stock (no MBC). Lately the car runs fine until I've been driving it for 10 minutes (car has been in the normal temperature as per the dash gauge the whole time after warming from cold), after which point the A/C stops working and the car won't boost past 6psi. The strange thing about the issue is that if I turn on the heater and recycle the 2-3 litres of coolant in the heater core/lines.... the A/C and boost comes back for a few minutes.

I think the car thinks it is overheating, not sure if it actually is. Two questions about this:
- Do the A/C clutch and VSV stop doing their thing when they believe the car is overheating? (Obviously these systems create more heat, so its logical that the ECU would stop them... but I haven't been able to confirm this)
- Could this be an air bubble in the system? The car does gurgle after a long drive, but its been doing that for years.

Thinking I might replace the two temp sensors and just flush the whole system. Its been a few years since I replaced the coolant.

Thanks!
Craig

Last edited by leusent; June 9th, 2019 at 14:29.
leusent is offline  
Sponsored Links
Advertisement
 
post #2 of 22 (permalink) Old June 9th, 2019, 16:29
Registered User
 
Join Date: Jan 2006
Location: Alexandra, New Zealand
Age: 58
Posts: 7,398
OldTrader Rating: (3)
The VSV will limit boost to waste gate pressure (6-7psi) if;
1/ Engine temp is not up to operating (90C).
2/ Ambient temp is below 0C.
3/ MAP pressure is below 0psi.
4/ Engine Knock not detected.

Not really sure the AC has turned off but would guess boost limitation is related to a faulty temp sensor. Remember you have 4 temp sensors (ambient, coolant at engine, IAC, Radiator). Some of these have several control functions so can cause a few issues.
benckj is offline  
post #3 of 22 (permalink) Old June 9th, 2019, 21:43 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Thanks Benckj,
I am wondering if the issue is with one or multiple of the temperature sensors. I am aware that generally the VSV will not operate until the engine is up to temp, but I'm not sure if the VSV will limit the boost if the engine is far past normal operating temperature (i.e. way over 90 degrees). And if that is the case, I thought it depended on the engine coolant sensor (not to be confused with the dashboard coolant sensor) only.

The A/C is an even bigger mystery.... when the A/C doesn't work because the freon pressure switch detects low freon, the idle up valve doesn't trigger. In my case, the engine is idling up but the A/C clutch isn't engaging. Weird. Also, I'm unclear if the A/C even cares about the temperature of the engine from any sensor (This was the closest thing I could find about it: https://www.mr2oc.com/6-mkii-90-99-n...ml#post6697026).

*If* the VSV depends on the coolant temp sensor and the A/C depends on the rad temp sensor... (two against one)... then it almost certainly means that the gauge temp sensor is sending the wrong reading and the car is actually overheating.... scary! I'm worried this could be the case, because when you turn on the heater the temperature of the air is scolding :/

But in any event, I welcome your thoughts and ideas.

Cheers.
Craig
leusent is offline  
Sponsored Links
Advertisement
 
post #4 of 22 (permalink) Old June 9th, 2019, 22:10
Registered User
 
Join Date: Jan 2006
Location: Alexandra, New Zealand
Age: 58
Posts: 7,398
OldTrader Rating: (3)
VSV will still allow boost if temp is above normal. Generally, this can lead to detonation & knock which will then limit boost. My guess is that the radiator temp sensor or wiring is poked leading to strange results. I'd try to unplug it and see how the engine & system reacts. Fans should come on and not turn off.
benckj is offline  
post #5 of 22 (permalink) Old June 13th, 2019, 12:45 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
I unplugged the rad temp sensor and noticed the fans kicked on right away. Drove it around a bit and the same thing happened. Its worth noting that perhaps the post-drive gargling comes faster (almost right away) and is louder than it was in the past. Maybe my rad cap has just gone bad? Its probably 5 years old.

Whats got me most perplexed about this is, I'm not really sure why the A/C is turning off. I thought that it would run just as long as the pressure safety switch was registering enough freon in the system. What other conditions are there that it is checking?

-Craig
leusent is offline  
post #6 of 22 (permalink) Old June 13th, 2019, 14:38
Registered User
 
Join Date: Feb 2016
Location: Maui, HI
Posts: 1,107
OldTrader Rating: (0)
The radiator fans and a/c system are controlled by the a/c amplifier, an autonomous ECU entirely independent of the main engine ECU that controls boost, ignition, fuel, et cetera. Hypothetically if your a/c compressor is failing intermittently and generating false knock this would cause the engine ECU to cut/limit boost at the same time that your a/c turns warm. Honestly IDK.
merryfrankster is offline  
post #7 of 22 (permalink) Old June 13th, 2019, 15:18 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Hey man, I do appreciate the thought. I see your point, perhaps the a/c compressor is doing something to trigger the knock sensor... but what I can't figure out is, why would turning on the heater make the compressor stop "knocking" / "failing" ?

My gut says the car is overheating. The gurgling after shutoff is pretty aggressive. I can see small amounts of steam appearing through the overflow tank. Reading the BGB I can't see anything about the A/C system shutting off due to high temps... though it does apparently take the water temp sensor as an input: 1991 MR2 BGB Online - Mechanical - Air Conditioning System

So *if* the A/C system does shutdown when the car is overheating, and if the car is overheating maybe it is knocking too... then I just need to stop the car from overheating.

But its all conjecture.
leusent is offline  
post #8 of 22 (permalink) Old June 13th, 2019, 15:30
Registered User
 
Join Date: Feb 2016
Location: Maui, HI
Posts: 1,107
OldTrader Rating: (0)
If you think the car is overheating and this is not confirmed by any of your sensors which could be junk aftermarket sensors or old wornout sensors for all we know then get an IR gun and point it at your radiator inlet or the water neck this will give you verification of your water temp.

PS. If your car is overheating this should trigger your fans. If the fans are not on with an overheat condition then you need to check the cooling system sensors, wiring, relays, et cetera, refer to the BGB trouble shooting section.

PPS> If you have fans on and still overheat this could mean any of the following blockage, air pocket, failed water pump, blown head gasket, et cetera.

Last edited by merryfrankster; June 13th, 2019 at 15:33.
merryfrankster is offline  
post #9 of 22 (permalink) Old June 13th, 2019, 16:07 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Good thinking. I do have an IR gun and I will give this a shot.

I noticed you did not list bad rad cap in your list of reasons. Wouldn't a bad cap cause a higher boiling temperature and therefore possibly cause steam pockets and overheating?

PS it is annoying to try and google "Why does my ac stop working when my car overheats" because you only get questions like "why does turning on my AC make my car overheat". Sort of the reverse problem I am having, heh.
leusent is offline  
post #10 of 22 (permalink) Old June 13th, 2019, 16:40 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
I do see in the BGB that the amplifier has a pin that goes to the ECU, presumably so that the ECU can control A/C operation.

Also: https://www.toymods.org.au/forums/th...=1#post1429924 suggests that generally toyota ECUs might have overheat protection for AC. Interesting... hurm.

Anyway, I will pack my IR gun and see what it tells me.
leusent is offline  
post #11 of 22 (permalink) Old June 18th, 2019, 12:25 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Took the car for a short trip today. Got it back home and when I pulled into the garage, the temp gauge was at its normal fully warmed up position. The car gurggled a bit, nothing really extreme. I'm not sure if boost was limited, local streets have a low speed limit.

My IR readings showed the coolant tree attached to the block was as hot as 120oC degrees (250F). The hard line going to the filler neck was 90 to 100oC... so right around the temp of the stock thermostat.

Strange thing is.... the hardlines going to the radiator in the frunk were 28oC (not much more than the outside ambient temp)??? Not sure why that would be, shouldn't they be about the water temp (90oC/190oF)? This is just getting weirder and weirder.

-Craig
leusent is offline  
post #12 of 22 (permalink) Old June 24th, 2019, 10:24 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Well I think the mystery is solved. I was driving the car around for progressively longer periods, getting out and hitting parts of the engine with my IR gun. The last trip I attempted was about 15 minutes and the car just went totally bananas, overheating and coolant boiling out of the system. Took it apart and found the thermostat was just stuck 100% closed. Guessing my dash thermometer isn't working too great, though when my car turned into a 65mph steam machine it did rise all the way to about 3/4ths (but never into the red).

I'll report back when I have the thermostat replaced. Interesting thing to discover here is that, at least a JDM Gen2 engine, does seem to limit boost and AC when hot.

-Craig

P.S. I am running an Gen2 altrac ECU, though seems doubtful that would make any difference.
leusent is offline  
post #13 of 22 (permalink) Old June 25th, 2019, 01:30
Registered User
 
Join Date: Jun 2019
Posts: 5
OldTrader Rating: (0)
having a similar issue in my towing truck which we use for ritewaytowingnyc.com I am also looking for the solutions.

Last edited by martinbrown349; June 25th, 2019 at 01:36.
martinbrown349 is offline  
post #14 of 22 (permalink) Old June 25th, 2019, 08:02
Registered User
 
wildhippie666's Avatar
 
Join Date: Jan 2007
Location: Newnan, GA
Age: 32
Posts: 598
OldTrader Rating: (8)
Quote:
Originally Posted by leusent View Post
Well I think the mystery is solved. I was driving the car around for progressively longer periods, getting out and hitting parts of the engine with my IR gun. The last trip I attempted was about 15 minutes and the car just went totally bananas, overheating and coolant boiling out of the system. Took it apart and found the thermostat was just stuck 100% closed. Guessing my dash thermometer isn't working too great, though when my car turned into a 65mph steam machine it did rise all the way to about 3/4ths (but never into the red).

I'll report back when I have the thermostat replaced. Interesting thing to discover here is that, at least a JDM Gen2 engine, does seem to limit boost and AC when hot.

-Craig

P.S. I am running an Gen2 altrac ECU, though seems doubtful that would make any difference.
Glad you solved the mystery!
The stock temperature gauge (not sensor) has a pretty large "dead spot" at "normal" temperature. This keeps the needle from fluctuating up and down as the t-stat opens and closes at normal operation. I've seen 'yotas overheat without the needle moving, in fact. It could be a bad sensor, or it could be the gauge's dead spot is out of calibration.
wildhippie666 is offline  
post #15 of 22 (permalink) Old June 25th, 2019, 12:54 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
Thanks for the insight about the deadspot. I guess that makes sense, so you get a nice uniform reading most of the time. Very interesting that you've seen Toyotas overheat with a seemingly healthy engine temp being reported! Anyway.... If I didn't blow the headgasket, I might embark on a little project to deploy a more accurate engine thermostat with a display in the cabin.

I never leave a thread hanging, so I will report back when I've got this all sown up.

Big thanks to everyone who responded and even those who just read this and kept up with my short little story here.

-Craig
leusent is offline  
post #16 of 22 (permalink) Old June 25th, 2019, 15:11
Registered User
 
Join Date: Oct 2012
Location: Wellington, New Zealand
Posts: 1,132
OldTrader Rating: (0)
When the sensor starts to get steam or air pockets around it, it can no longer read temps properly so freaks out. It only works properly when fully immersed in water/coolant.
GDII is offline  
post #17 of 22 (permalink) Old June 25th, 2019, 15:44 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
I suppose the issue could be that the engine was steaming this whole time, though I didn't see anything coming out from the engine bay until the "big steam" last week. Heat was working and the CEL wasn't on. Last week it seemed that the engine hit a tipping point, once it got hot enough to start bubbling everything went over the edge. I lost cabin heat and I starting making * alot * of steam.
leusent is offline  
post #18 of 22 (permalink) Old July 4th, 2019, 12:38 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
I opted for a 170oF thermostat and got it installed with a 70/30 mix of coolant. The gauge settles between 1/4th and 1/3rd of the way up now, much lower than before. No gurgling after shutoff anymore, even after a long drive, and the AC and boost are working great. Problem solved!

-Craig
leusent is offline  
post #19 of 22 (permalink) Old July 8th, 2019, 00:12
Registered User
 
Join Date: Oct 2012
Location: Wellington, New Zealand
Posts: 1,132
OldTrader Rating: (0)
Interesting. That's quite a cold thermostat and the gauge reading there is not usual. Seems like there is some other issue still going on being masked by the thermostat. The ECU might still think the engine is warming up modifying the fuel map to run rich.
GDII is offline  
post #20 of 22 (permalink) Old July 8th, 2019, 12:04 Thread Starter
Registered User
 
Join Date: Jun 2017
Posts: 19
OldTrader Rating: (0)
What makes you think there is still some issue? The car is running normally again, with the boost and A/C working fine. The temp gauge is reading a little low, but I attribute that to using a 170oF thermostat instead of 180oF. I know there is some debate about which thermostat is best, but I willing to suffer the slightly worse-off fuel eco of the colder engine to stop the post-drive gurgling that I was facing for years before.

-Craig
leusent is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MR2 Owners Club Message Board forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: (1 members)
Del91T
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome