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Overheats less in 3

1041 Views 10 Replies 6 Participants Last post by  tateos
Hi all. First post. Thanks for having the forum! Lots of good info.

I have a question with which I hoped someone could help. 1997 Concours. New car for me. Many thanks to the dealer for full disclosure!!! :D It runs around town just fine all day, but it overheats on hills at interstate speeds. It MOST LIKELY has compromised head gaskets. Everything SEEMS to flow well. Stat/cap are new. Haven't had time to test for gases or look at water pump yet.

So I'm a glutton for punishment and decided to drive it from Arkansas to Cincinnati. Eventually I figure out that it is MUCH less prone to overheating if run in "3" instead of "D", even though RPM much higher. That seemed odd to me. I just rationalized it with the gasket issue by assuming pump more efficient and pushing combustion gases through purge line at a higher rate. The vapor then venting without issue until too much hill stress creates a huge bubble at the pump causing cavitation (when the gauge "runs for the red" the heater stops blowing hot).

Is that a valid assumption? I'd love to find out that the water pump is just crapping out. That thing ran like a champ up to 70 in "3" all through flat Indiana/Illinois, and even cranked up to 80 as I "roller-coastered" the Missouri hills. I had cruise set on 65 in "3" for hours at a time on the flats.

Anyhoo, I was curious about that oddity and thought I'd ask the experts why a compromised head gasket would be LESS finicky at higher RPM's. Thanks for any answers!!

ps- Also, best strategy for pulling temp back was crank heater, slow to ~30 and shift into 2nd. This seemed to bring it back pretty efficiently and prevent the need to stop.
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Head gasket(s) is/are shot and multiple head bolt holes in the block are stripped - you need to repair it or have it repaired. Driving in 3 will eventually burn out the trans, the motor, and enough extra gas to pay for the repair.

I did Norms, but I would do this if I have to do it again on another N*:
tateos has, unfortunately, "been there, done that".

Get a coolant gas test kit ($50) from NAPA and confirm/deny the presence of exhaust hydrocarbons in the airspace above the coolant in the surge tank. This will definitely give you your next course of action. (Fortunately, you're only in for a top overhaul.....leave the lower end alone.)
. Driving in 3 will eventually burn out the trans, the motor,
Can you explain how it will burn out the motor and trans...
I appreciate the responses.

I figure it's the bolts, but I was curious about why higher RPM (engine working harder, assumed hotter and lots more combustion gases pushing at the gasket) made it LESS likely to lift to the point of gasket breach. I mean shifting to "2" and running 3 grand actually pulled the temps down!!

I'm going to grab that Block Test kit, but if it's single use I probably won't use it until I have another episode. My untrained "smeller" seems to indicate exhaust in the surge tank after runs-for-the-red, but not under town driving. (Though that could be the smell of these new-fangled coolants when hot.) I drove it daily for 2 or 3 weeks prior to trying the 1500 mile round overheats, no coolant loss, no "chemical-like" smells from the surge tank. That included flat highway use in "D", though I kept RPM right under 2000 on on-ramps.

I was curious about the "burn up " issue as well. I never once hit 4 grand, and was generally only turning about 2900-3100. Mileage did stink at 22 mpg though.

I just hope it continues its "around town" good behavior because I'd like to get some use out of it before another investment. With that said, is it stupid of me to assume that coolant will stay out of the oil (my main concern)? Will the "oil life indicator" drop quickly if that type of breach occurs? Sure wish the Jake fellow lived around Arkansas instead of Canada!!

Thanks for any and all help!
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Engine load is lower with higher RPMs. The same amount of work is done, but spread over more revolutions (combustion cycles). Lower cylinder pressures. This is why it stays cooler.

Send me plane tickets to Arkansaw and you've hired yourself a Northstar mechanic! I've never been to your state before.
High rpm moves one hell of a lot of coolant through the system: the Northstar system, when properly bled and pressurized, will cool a 747. The Northstar will run for years at 3,000. There is actually less combustion chamber pressure at high rpm/low load than during acceleration.

IF you ran the engine/trans at 3,000 - 3,500 all day pulling trailers up a hill, you might do some damage. I would bet that a 2000+ Northstar will run at 4,000 rpm forever, partly due to the roller cam followers. Your car has the older style "flat tappet" lifters (direct-acting) so there's a lot more scuff wear there.........but it won't be affected +/- at 3,000 rpm.........

The engine is redlined at about 6,300. (Conservative valve float precaution). It will run there all day long. It's the driven accessories that come apart. The Northstar has really no piston stroke compared to older OHV engines: The Northstar piston travel is more of a vibration in the cylinder than a stroke.......:rolleyes:

EDIT----Take Jake up on his offer - whatever the cost. Jake, hope you like good barbecue: beef and hog.
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AHHH HA!!!! (bells going off and light bulbs appearing) You guys are giving me some learnin now! I appreciate it. Work being the moving of 4000 lbs from point A to point B, divided by revs, making work per rev (thus work per cylinder fire) lower. Sweet.

I'll keep giving this thing the look-listen-feel inspection to see how much future cash I want to spend on it. Heck, I just got back from my daily commute on the Interstate at 70 mph in "D". 98% of my driving for the next year will be local, and the trusty old F150 will do the long stuff. At a minimum, I think I'll be stubborn/stupid enough to eventually order Jake's stud kit and give that a go. If I can't find the time, I might seriously consider the ticket!! And there's always the very real chance that I order the kit, get halfway through the job, then beg him to let me fly him down here to fix my mess!!

I want to thank you all again for the forum. Just the learning/hobby aspect of this will be worth a portion of the ~2 grand I let myself get rooked out of on this deal! The local-drive AC/comfort/stereo is worth a portion too.
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Can you explain how it will burn out the motor and trans...
My logic is: Much higher revs means more wear in the engine, gears turning faster in the trans, extra heat produced, also is there TC lockup in 3rd? - all bad for longevity
So, then even more revs and wasted gas and excess heat and excess wear
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