How hot is too hot?

AndrewHadji

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May 10, 2015
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So asking the brain trust. Seen a lot of coolant/overheating questions. Should start my own. I have an engine watchdog connected to the headbolt closest to the coolant outlet.

So i dont overheat, but i do get warmer than before I turboed. it seems 190 on the watchdog is a little under half way on the stock gauge. I graze 202 on a steep climb and going faster than 70 mph with the ac, otherwise 190 seems to be where she sits mostly. 202 seems to be 2/3rds, half way between the half way and the red on the gauge if that makes sense

How does this align with turboed folks? It never sits on 202 very long, maybe a min or two. Everything seems to be working correctly as the temps come down pretty quickly if i cruise at 65.

Looking for other temps for those that have turboed. Does this sound similar? And is 202 higher than I should like?
 

coldtaco

 
 
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Jul 3, 2004
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Anchorage, AK
on my turbo'd 2H just above middle was showing about 245F on my aux gauge, so can't imagine what temps are closer to red line. Don't know if temp readings are the same, or max temps are the same between the 2H and the HZ. After all the work on the cooling system, including getting a custom built 2in longer (on the bottom) radiator I finally got my temps under pretty good control. We have on 5mi hill climb near hear and before I got the new radiator the water temp would outclimb the egt's, then with the new radiator the egt's outclimbed the water temps. But the head cracked last summer so I think I did the damage way before then but the cracks held together for a while. mine would sit at about 190 at 65mph all day long at the end. I would have to re-read my build thread, or you could ;)
 

GTSSportCoupe

2LTE whisperer
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Mar 23, 2012
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Victoria, BC, Canada
The problem with the turbo IDI's, is there is a lot of heat around the pre-cups in the cylinder head. So even though your cooling system as a whole is not overheating, there can still be localized boiling around the pre-cups. Think water boiling in a cast iron frying pan on your stove. You know all those bubbles on the bottom? That is what is happening at the hot spots in your cylinder head. This vapor actually prevents sufficient cooling of those hot spots; which means they get even hotter. If this happens regularly, it leads to a cracked cylinder head.

So when your total cooling system water temps start getting up there, it means you are running closer to the edge in the cylinder head. Not a good thing.

Now those of us with LJ78's know this problem well (a factory turbo IDI engine). My recommendation to those in the LJ world, is don't run the factory temp gauge over half. More ideally around 1/3.

Personally I've gone to evans waterless coolant, which doesn't boil until 380f. I hit the red on my factory gauge at least a couple times every year when I'm towing my 16' camper up long grades in hot summer weather (truck and trailer weight is 8500-9000lb) Seven years of that now and I haven't damaged my cylinder head yet. I can only chalk it up to the Evans preventing the localized boiling which stresses the head. The stuff does have it's disadvantages tho....
 

AndrewHadji

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Gotta flush all the water out.... 3 percent or less.... need to carry spare as doesn't seem to be readily avail least in my area
 

FJBen

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Apr 1, 2004
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Disadvantages of Evans?
Higher Cylinder Head Temps.. However, since Evans has a higher boiling point, you won't get the problem of boiling off and non-cooling in those areas. If that higher temp causes any issues with a 1HZ/IDI engine, I don't know but is another potential downside.
 

GTSSportCoupe

2LTE whisperer
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Mar 23, 2012
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Victoria, BC, Canada
Disadvantages of Evans that I'm aware of (having used it quite a few years now):

- Its not as efficient as water at transferring heat, so your total coolant temps will be a bit higher under load. Although this sounds bad, the stuff will still be protecting against localized boiling in the head, so the total head temp will be much more even. So will protect against what kills the IDI cylinder heads.

- It does gel at very low temperatures. It's not really recommended for diesel engine heaters or even electric block heaters.

- It's expensive and a PITA to install.

- In a pinch it does mix fine with water, but you loose the advantages of it as soon as you add water.

For me the advantages have out-weighted the disadvantages. I have no doubt it's saved my 2LTE cylinder head thus far. I abuse my engine heavily when towing in summer.
 
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