Suggestions re overheating 240z

[aussie240z]

Guys

I am hoping to get some suggestions to assist. I have a 240z engine  that has just been rebuilt, completely from the ground up. Oversize by 30thou, port polish, ATF 2 cam etc. The radiator is 3 row, had the tanks off, rod cleaned etc, new water pump with engine build, new Nissan 71c thermostat, new radiator cap. Did overhaul of fan clutch but then replaced with elwctric thermostat controlled 12" fan (front mount). Car has been on dyno and triple webers balanced and jetted accurately. Behavior is that car runs fine, drive for 1/2 an hour and temp goes up from normal after start then starts to climb. Gets to around 170f and higher and then starts to blow off excess pressure. Can't see anything blowing pressure into water jackets that would show issues with head gasket or similar. Am going to try removing thermostat and just use the electric thermo switch but that seems at odds with normal practise.

Appreciate any suggestions/ideas as I am at a loss to cure this issue.

Cheers

Ian

 

[peter mc]

mmmm its so hard to find these problems over the net ... i had a engine a wile ago that had a the same problem and it had a small crack in the head it was fine for 20 min then it would get very hot, so i think u will have to look very hard and most likely have to take it apart ...... but i have also had a thermostat do it to

[Wayne G]

170f is not hot, actually about right for 71c thermostat.  Perhaps the cap is faulty or not seating correctly in radiator?  Perhaps the gauge is faulty and it is actually hotter?

[Linton]

taking out the thermostat can cause o/heating as well, the water has no restriction to give the radiator time to cool the water, If you are sure the h/gasket is good you might change the t/stat to a lower temp or at the very least check its operation and as the others mention recheck  the r/cap, wouldn be the first time I overlooked a simple fix.

Linton

[dat2kman]

Water bpils, produces steam etc at 212 deg F it expands in volume as soon as it starts to get warm, ie from approx 80 deg F.

A 14 pound radiator cap, on a sealed system will raise the boil point to 240 deg F ie approx 120 deg C

 

Your issue could be, ypur new radiator cap is a " recovery" type, not a full seal type.

A recovery rad cap should be combined with a recovery overflow bottle that has a normal sealed rad cap fitted, i use this system in all race cars, adds security and allows expansion and stops overflow, but i do have a overflow bott

E from the recovery can ( to stop dumping fluid on track)

 

Other good idea is use a watwr wetter like Redline or Penrite Sin, this acts as a conductor between the eatwr in the system and all metal components. Ethylene glycol, (antifreeze) acts as an insulator, thus pteventing heat generated in tne metal to be conducted to the watwr. System needs a absolutely thourough clean it before use.

Lowers opetating temps by up to 20 deg F in my cars on a like for like comparison

 

Two weeks back, all thos eas coveted by anptjer tjread, have a trawl tjrpugh, or can someone link it to hete?

[Zedman240®]

I've had new thermostats jam shut from new... I'd remove the thermostat and check it opens sufficiently in some boiling water. Also check how much it opens...

[MaygZ]

How recently was it 'rebuilt'?  Was the head re-torqued after the first warm up?  You may find that you have a little blow-by of compression gasses that could be solved by a re-torque of the head.

 

Is the fan coming on at temp and is it staying on until cooled?

 

What are the chances that you are now revving quite a bit faster with you new sweet motor, and the extra RPM is causing water cavitation from the faster revving water pump?

 

Other than that, what the other guys said.

 

By the way Dat2kman.  Please turn on the study light when you're typing. 

[aussie240z]

thanks for all the suggestions. A couple of responses.

the engine was rebuilt and went "live" about two months back. Head was retorqued as suggested by normal process. Have since checked again and is down to spec. Havent run the car hard at all yet so not too much chance of over revving yet..

the old clutch fan was replaced with electric fan, with adjustable thermo switch. have tried setting at various levels but still overheating.

The rad cap is a non recovery type so shouldn't be an issue with blow by on that.

The behavior is heating up to op temp, then runs for a little while and then start to go up with pressure/temp. Sort of indicates a leak somewhere from past experiences.

Plan for the weekend is to grab a leak test kit from repco and test the radiator fluid for combustion gasses. If that shows positive, then a leak somewhere and  tear down and check. If nothing there, will also take the thermostat out and check that for correct operation. Will see what transpires.

Appreciate the collective assistance

 

[dazzed]

Im pretty sure yoou should be running a 82 degree thermostat, when the engine was first started did it get really hot before the thermostat opened? as a new stat takes a lot longer to melt the wax inside the pellet before the stat opens ,and then the block recieves a gush of cold water whick causes thermal shock and head gasket problems.

[aussie240z]

I did have a higher (Tridon) thermo in from the engine rebuild. Replaced post running with the Nissan one. Don't remember the temp setting on it. The big test will be the leak tester and see whether any combustion gasses coming through the radiator water. Everything else having been ruled out, sort of feels like head gasket or head issue. 

[dazzed]

I had 30 tridont thermostats in a shoe box i fitted to vehicles that had 3 year warranty and all failed ,and the distributor refused to back the warranty , said i was stupid and didnt know what i was doing, now you mention you fitted one all your problems have now been associated with just that, you may have a crack in either the block or the head, and is going to be a daunting task to prove , im not saying that its exactely the problem but a good place to start your diagnosis, cheers Daz

[dazzed]

And the problem is that a leak test will not show up or be indicated untill the engine climbes up to a tempature that is higher enough to expand the engine to open up a apurature or crack that can effect cooling

[aussie240z]

The tridon went and the nissan one went in. Now, the combustion leak test is the next plan and true, the check when up to op temp is the only way to make sure. Am intending to run on the weekend and see what results i get. If need be, will drop the head and magnaflux the unit. Not an exercise i want to do again and pull the head off but probably only way to make sure. 

[dazzed]

I have a 6 cylinder twin cam toyota that has exactely the same symptoms and have had the head off and crack tested,with no crack showing up, so i can only assume the cyl head is cracked internally which is difficult to detect, let us know how you go, cheers Daz

[Patch]

Chemiweld is good stuff, I have used it on a Cressida where the water is pouring out exhaust, water in the oil, oil in the water and running rough, comes all good and got 5 years out of it having to use another bottle each year as it blew though, ended up blown head gasket, yet my bobcat that had a cracked head has been going 6 years on one bottle .

[dazzed]

Chemiweld is good stuff, I have used it on a Cressida where the water is pouring out exhaust, water in the oil, oil in the water and running rough, comes all good and got 5 years out of it having to use another bottle each year as it blew though, ended up blown head gasket, yet my bobcat that had a cracked head has been going 6 years on one bottle .

thats exactely what i did , only lasted about a year ,then did it again