348 Odd Overheating Problem

First off, 91TS, been fighting with this problem for quite some time. Problem= start car, drive until fully warm(90C)... highway cruising will stay around 90C/194F. If I drive into town, traffic jam, etc, temps will climb to 115C/239F and slowly cool off 'somewhat' with fans running full time. Fans kick in normally. The temps will not come back down enough for fans to shut off(or seems like forever) unless getting back on highway for .5kms.
Things that have been done:
New water pump (Ricambi) 4k kms (last year)
Flushed rads a couple of times, can see light from other side of rads, compressed air from backside with cleaning solution.
Bled system 16x, heater on, etc...!
Watered(distilled) down coolant to see if that might help... no major difference
Changed old rad cap(.9bar) for a 1.1 Bar... pressure tested new cap. all good
Pressure tested cooling system 16lbs (engine hot & cold)for 20 minutes each, no loss in pressure
Checked all spark plugs for possible 'sauna bathing' all clean/lean & normal
no white smoke from exhaust
used Block Tester to check for any 'containation' of coolant with engine running.... is a tester that changes color if combustion gases are present.... all clean, no head gasket leakage...
There are 3 ideas that I haven't done yet...
Change out thermostat... but, in my view, thermostats tend to stick open, or in my case if stuck closed, engine would overheat almost immediately???
Pull the rads and have them steam cleaned, inside & out.... have run cleaning crap through them and flushed???
Water-Wetter... will help, but there has to be another problem...
Anyway, any thoughts welcome.... thanks so much

 

Thanks for your quick replies.
Yes, both fans are operating properly.
I thought head gasket but did the 'Block Test' to see if there were any gases in the coolant. Basically you remove the rad cap, warm up engine, and place the tester filled (to line) with test liquid(blue) in place of rad cap, and squeeze bubble for 5 mins sucking up any gases within the coolant tank that might be coming from a leaking gasket. Did this test a couple of times, no color change. Actually screwed the rad pressure tester on when hot/running pressurized to 15lbs to see if I could get a rise/or drop in pressure.... stayed the same???... but not on for too long.

This is getting stupid.... drove car tonight, temps stayed just around 88>92C for most of the drive. Only after filling for gas did it move up, but then again I was on it for a bit, then cooled back down to 90C fairly reasonably in time????
It may still be a head gasket, just trying not to pull engine and find out it was something stupid

 

Hmm... that did cross my mind about a thermostat not opening fully! Years ago, I had heating problems with a liquid cooled snowmobile engine. What I discovered when diagnosing, was the thermostat shaft had bent, (heat most likely)and would never open more than a quarter lift. Miroljub, you have something there.... Time to pull the thermostat, if only to cross that off. The engine does seem to run fine/cool until traffic, or downtown city street/stop, go, stop. At that time, both fans are trying to cool, but it takes quite some time to get back to a normal temp... usually by getting out on open road, and then the fans shut down. When driven hard, the temp will rise a bit, maybe somewhat more than expected.... but I'm MOVING... and the air through the rads will help in this regard. I will try to pull the thermostat tomorrow... just know it's a PITA, removing the engine cover, etc, and working out the roof! LOL!

 

OK, pulled the thermostat, verified that it opens/closes at proper temps... and it did!!! I suspected it would as when it warms up driving, I can see the fluctuation on the temp gauge as it opens, draws cooler reserve, opens, and so on.
So..oo. that leaves me with a head gasket headache! Unless someone can come up with another alternative, I'll be pulling the engine tomorrow. GrrR!
Anyways, drained all the coolant out again, inner wheel wells out, spraying all open threads with penetrating oil and just called it a day.
Maybe it's a good thing as I'll be able to get to some oil sweat/leaks that have been bugging me since the last major. Wish Ferrari engines had that Japanese O-ring case sealing.... I'll be more stringent in my assembly this time!
Again... if anyone has another suggestion before I pull it, I'm all ears,,, LOL!

 

Well, again, thanks for more of your replies. I agree with all of you and it's obviously somewhat hard to describe every little detail in this problem. I'll try... The car had some background but the last previous owner proved himself to be not too honest.... # of issues definitely known to him and not forthcoming. I'll stop on that as I don't want to write a book! History was good until about 2008.... then the car sat, with very little time on road until 2016. I have cleaned up most of the issues, except for this irritant! I have never overheated this engine, but it has gotten pretty hot. That said, I'll never know what might have happened with the PO ownership. I've changed out coolant more times than I care to count, flushing, purging air, etc. Of note, the driver's side rad looks almost new, passenger side probably original. I was thinking maybe I would pull the rads 1st, passenger side anyway, to verify how ugly they may be.
To 'TIM', I will attempt to refill all coolant, purge air, etc, then take it for a good drive. I will leave the inner wheel wells off, and pull out my handy dandy infra red temp sensor, and try to verify any differences in temps. While purging air after warm-up today, I looked for 'bubbles' in the tank, saw none, but then it was getting hot(100+C) and the tank was starting to burp and splash coolant. Cap had to go back on. Fans ran as normal, shutting down later when the fans had done their job, albeit they ran alot longer than expected to bring down the temps.
All the 'tests' that I have previously have suggested good head gaskets, but gaskets are funny, sometimes hidden until apart. I'm wearing down, frustrated, and I'm not used to not being able to diag, and just guess!

 

OK, I decided to pull both rads today, and see how bad/good they were. Took my time with it, passenger side a bit of a pain(bolts holding oil rad to water rad), but they're out!
After flushing them thoroughly, they seem to be pretty good, not too much crap... but what do I know! LOL! Certainly someone else has spent big bucks on new ones in the past cause these are not 27 yrs old. Tomorrow am they are going for a steam cleaning and verify that they will flow properly at a reputable rad shop. Depending on time, I will remount them and go for a drive later, or Wed am, try the infrared temp reader and report back. If this doesn't clean it up then motor will have to be pulled... I'm out of options!

 

Not sure exactly which hose you're talking about. Do you mean the small coolant hose leaving from the lower rear of the coolant tank? If so, I'll look in am

 

Hey, thanks again guys. Nick, I wondered about the condition of that hose, as it felt 'harder' than the reg flexible hose. Will replace this am while getting the rads cleaned. thanks.... Mats, your read is right on.... exactly the problem. I know the drivers side fan puts out a good blast of air, never really checked the output of the passenger side, other than hearing the fan kick in, and fitting fingers in between the rear tire and fender. (lowered w/19" tires, not lots of room) and feeling the blowing air. When pulling the fans and rads, the passenger side fan electrical connector was partly dissolved w/ lots of corrosion, so I believe (after your thoughts) that passenger fan would be running at maybe 50%.(guess from corrosion!) And, it would make sense in why it takes so long to cool back down. Do you have a part#, more info, on the fans that you replaced. Fan connection was going to be replaced today anyway. Who knows, maybe this will all pay off.... thanks everyone.

 

Well, at least I'll know that the cooling system will all be in order.... by the end of today/tomorrow....
BTW... that hose you suggested checking.... I actually replaced that in the major last year because it was fairly hard/old. Just went & checked this am... knew there was something about it when you mentioned it, just didn't remember replacing it...

 

Miroljub, that's a great looking fix for some poor engineering!!!
Today, the rads went in to get tested and cleaned up. They turned out to be in great condition..... somehow I was hoping for a problem....! Anyway remounted everything, new connectors and heat shrink everything. Tested all fan motors... all good! Pulled that hose that Pangea & Miroljub were suggesting, no problems with any corrosion, etc. I'm a bit apprehensive that I didn't find any solid problem other than the corrosion of the right fan connection. I will fill with coolant, and bleed tomorrow, then go for a drive and see. You never know, maybe the corroded fan connection was drawing big amps and turning half speed???? In any event, I'll know that the coolant system is A1...