Since it's so hot out these days...

[IHI-RHC7]

I have a Q.
Recently, the supra started showing some very odd cooling characteristics. The outside temperature was around 95 or so, and as I came down from cruising speed to stop and go portland traffic, the temp gauge started fluctuating like it does under boost with a BHG. What is odd, is that when I romped on it, instead of going up, like with a bhg, the temp jumped back down. This seems like a classic hot rod syndrome, with the mechanical fan not moving enough air at idle to cool the system down. The ac was on, and it was hot as hell outside, so I figured I might need to upgrade fans and radiator to keep things in check during the hot summer months.
So after it cooled down for good, I hopped on the dyno, made 4 4th gear pulls, and the temp didn't budge. The huge fans were blowing away, and apparently it kept things in check.
On the way home, things were fine until I hit traffic, and it started fluctuating again. Right when it was almost up to the H, I found a break in trafic and got up to 70, and it cooled right back down. But then it started dancing up and down even at speed. Only when I went through shade would it settle down. Still, boost made things better, rather than worse. When I let off the throttle, it heated up. It ran this way for 50 miles or so, and then was fine for the remaining 10 miles home. Until I got to the driveway, then it heated up. I parked it and let the turbo timer count down, and it stabilized right before the car shut off.

So what's it sound like to you? I pulled the thermostat, and tested it. It is fine. It's a 93 deg unit, so I'm replacing it with an 85 deg unit. The water pump usually weeps before it stops pumping correctly, right? The headgasket is a year old Titan 1.5mm torqued with ARP studs to 90 ft.lbs. The coolant was flushed last summer, and it didn't have any cooling problems all last summer or this winter. Also, turning the heater on full blast had NO effect on temperature. It seems that if the headgasket was to blame, then the temp would have gone up under boost, and been fine when cruising, but this was NOT the case. Do you think I just need more airflow? Or a bigger radiator? Or is there a mechanical problem with the motor? I'm compression testing it this weekend to see if I've lifted the head, but I'm really doubting this is the problem due to the erratic charactaristics of the problem. Any insight would be most appreciated. It semms that plenty of us are having cooling issues this summer.

Thanks in advance!
-Jake and Heidi

 

[siman]

Mine does the same.

My temp gauge fluctuates around 2 bars....under WOT and slowing down runs on backroads ( not a floating gauge though) it lowers because of the higher rpm use...the fan is going faster and teh air is obviously hitting the radiator faster.....so better cooling effenciancy.


I thought my temp gauge or thermostat was quirky for the longest time...but over 11K miles from the rebuild its not the HG or the brand new water pump or thermostat!

its just the way the car cools....funny.

I think you are fine. If it was something REALLY bad...the car would overheat or start weaping coolant ( if water pump is blown, you were 100% correct there).

-Jonathan

 

[TONY!]

Some of following is of course speculative:

… the temp gauge started fluctuating like it does under boost with a BHG.

Are you sure you don’t have air pockets in the cooling system or a leaky hose? (Just want to make sure.) If you have a leak in your cooling system, maybe air pockets are to blame? Air in the system is a problem for coolant to circulate. Enough air in the system or running low makes the coolant harder to be pumped up and over the air pocket because of the difference in weight of coolant to air.
Coolant system pressure testing is an option.

What is odd, is that when I romped on it, instead of going up, like with a bhg, the temp jumped back down. …

…On the way home, things were fine until I hit traffic, and it started fluctuating again. Right when it was almost up to the H, I found a break in trafic and got up to 70, and it cooled right back down. But then it started dancing up and down even at speed …

…When I let off the throttle, it heated up. It ran this way for 50 miles or so, and then was fine for the remaining 10 miles home. Until I got to the driveway, then it heated up. I parked it and let the turbo timer count down, and it stabilized right before the car shut off…

So what's it sound like to you? …

CIRCULATION
Sounds like it happens when you have the RPM’s low. The water pump works in relation to the RPM’s. For some reason lower RPM’s are not enough to get things circulating properly. Another possible cause of poor circulation would be a pinched hose, or too much scale in the system. How well do you know the car or its history? If it is scale, here is a post on removing that based on my conversation with a friend:
Post 12 of http://supramania.com/forums/showthread.php?t=4050

… Chemically:
Now there is also a chemical cleaner you can use that is (according to my friend) only available at the dealer. It is supposed to remove any built up crap in the system. As far as the way it was mentioned to me, it is much stronger than what you would get from an Advanced Auto Parts or other stores like that.

…I'm compression testing it this weekend to see if I've lifted the head…

Doing a compression test for what reason? Personally, I like leak down testing over compression testing. It is easier to pinpoint what is your problem as you can feel and hear where the leak is sometimes. I will now shamelessly provide my write up on that:
http://supramania.com/forums/showthread.php?t=2229

If you are trying to figure out if it is BHG, a compression test ranks as third IMO as diagnosing that. A block test is much easier to do – all you have to do is remove the radiator cap and test. If you should feel like you have a BHG after other steps are considered, here are my thoughts on BHG’s:
http://supramania.com/forums/showthread.php?t=251

Any insight would be most appreciated. It semms that plenty of us are having cooling issues this summer.

I have noticed that myself even from reading SF also.

Thanks in advance!
-Jake and Heidi

Thanks in advance for writing your post clearly. I tried to respond to this one guy’s response to me at SF, and with all his typos and extremely poor writing, I wasted 20 minutes just trying to figure out what the hell he was saying.

 

[supraman7mgte]

could be bad sensor or gauge. did the car still run while it was tripping out?

 

[Yawgmoth]

The heat wave is horrid, I have occasionally noticed strange problems with my temp as well, but I burped the system and it pretty much eradicated it.

 

[IHI-RHC7]

Thanks Everybody. I'm going to comp test it because I have a compression tester, and I don't have a block tester. I will buy a block tester if I determine that I have tested everything that can be tested for free and still have a problem. The car has been maintained meticulously at the dealership. We are the second owners and last summer, we completely flushed the cooling system. I went so far as to remove the heater hose and blow through the block before and after to get every last bit out. I did not flush it with a hose, as this can damage the block, radiator, thermostat, etc... I used Prestone radiator flush and cleaner, and ran it through 3 cycles to thoroughly clean the system. When I started, there was a ton of restriction when I blew through the block. When I was finished, it was restriction free. You think another flush, 1 year later, and less than 10,000 miles could be beneficial?
Other posible problems are the massive blitz 4 core and B&M supercooler sitting in front of the radiator. The stock fan shroud has a bit of a crack in it, but I have the two A/C fans and the one auxiliary fan in front of the radiator. All electric fans are working perfectly.
So, what are the chances that all is well and I just need a bigger, more alluminum radiator?
Tony: The thing that frustrates me is that with a BHG, boost should push exhaust into the coolant, thus raising temps. How could boost possibly cool the temps? I can't think of how higher cylinder pressure could have a cooling effect.
Last question. Could the clutch fan be the one to blame?
I'll check the TSRM and test it.
Thanks again!

 

[TONY!]

… and last summer, we completely flushed the cooling system. I went so far as to remove the heater hose and blow through the block before and after to get every last bit out….

IF it was scale, you would need more than just a physical flush, but a chemical one …

…I did not flush it with a hose, as this can damage the block, radiator, thermostat, etc...

Or it could blow hoses or gaskets also IF you give it too much pressure. When I have done those flushes, I had the engine drain plug open, the radiator cap open, and the radiator drain plug open as well. When I turn the water on, I use in my own sense on how much pressure to give it – you can vary the pressure you give the water hose.

…I used Prestone radiator flush and cleaner, and ran it through 3 cycles to thoroughly clean the system. When I started, there was a ton of restriction when I blew through the block. When I was finished, it was restriction free...

Now I don’t know from my own experience, but my buddy that works at a Chevy dealer (the one I mentioned), made it sound as if there are over the counter flushes and then there are the ones used by the pros that are industrial grade. I know that some chemicals/products are not to be sold to the general public, but only to trained folks. I know that is true to some extent on some autobody supplies. From the way my friend made it sound, the stuff that they use at his shop is the real deal and that the Prestone stuff is the watered down version. But I did not see that product he was talking about first hand, I only heard how well it has fixed some problems.

…Tony: The thing that frustrates me is that with a BHG, boost should push exhaust into the coolant, thus raising temps. How could boost possibly cool the temps? I can't think of how higher cylinder pressure could have a cooling effect.

Based on what I know, it is completely incomprehensible – so I dismissed it. I instead considered that the cooling was happening as a result of higher RPM’s. Higher RPM’s make the water pump work faster. True, you may see your boost going up and true, boost and RPM’s do not always work in exact relation to one another, but you can’t get boost without having a minimum of RPM's. And so I suspected higher RPM’s instead of boost. RPM’s increase circulation, and that’s the reason why I suspected circulation.

...Could the clutch fan be the one to blame?
I'll check the TSRM and test it.…

I really don’t know, maybe my suspicions of poor circulation are wrong. I could not find info on checking the fan clutch and I did wonder what procedure you are talking about – what page is that? It is not in the Cooling System section, but I am interested in assess in fan clutches. Here are some other causes (I found that after making this post and my unsuccessful search for the procedure you mentioned):
http://www.cygnusx1.net/supra/library/TSRM/co/CO_04.html