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Thread: overheating race car - stumped!

  1. #1
    Registered User cbuczesk's Avatar
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    Default overheating race car - stumped!

    I have a 1972 240Z that I race in ITS. I built a new engine and used it for a race weekend last month without any issues except for a miss that would kick in around 6400-6600 RPMs. After the race I rebuilt the carbs and took the car for a drive. The miss was still there but everything else was fine including water temp.

    I went out for qualifying Saturday morning and had the annoying miss but water temp was good. I swapped out the MSD 6 digital with the MSD 6AL that I used last year in an attempt to fix the miss. The race was Saturday afternoon and the miss was a little better but the water temp got up to almost 260 on the 6th lap so I came in. There was so much pressure in the system that the overflow hose blew out of the catch bottle! Once the car cooled I removed the thermostat.

    It was warmer Sunday and on the 3rd lap of qualifying the temp hit 240 and I came in. This time I put on a known good water pump and a new radiator cap. I ran the engine with the cap off and I could see coolant flowing in the radiator. The front carb was running lean so we adjusted it. In the race the car hit 240 on lap 3 and I backed it down. I was able to complete the race by racing 2 laps and then coasting down the front straight and short shifting a lap and repeating that process.

    I'd appreciate any ideas!

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Chuck

    A few questions. Is the miss still there? Did you break in your new engine properly? What shape is the radiator (and cap) in? I would start with the obvious, pull the plugs and see what's going on there. If you have a miss that's still there you clearly have an issue of some sort.

    Just a few suggestions
    Jan
    1976 280Z
    HLS30288273

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    Registered User madkaw's Avatar
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    You swapped out ignitions-did this change any of your timing parameters?
    Have you done a radiator pressure check to insure no HG defect?
    Do you run with a thermostat? If so, what kind?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by Pomorza View Post
    I would start with the obvious, pull the plugs and see what's going on there.
    Instead of obvious, scary might be more appropriate. Headgasket,maybe? New engine, cylinder misfire and overheating.
    1976 280Z, with some minor modifications

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    Registered User cbuczesk's Avatar
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    The miss is still there but it doesn't happen until 6700RPMs. I'm thinking that the problem is with the distributor and that the digital MSD is more sensitive than the analog that's in it now. I'll post a link to my in-car camera tonight so you can hear the miss. You might be able to read the temp gauge too.

    I broke in the engine properly. 20 over pistons, new bearings, etc. The engine has to remain mostly stock for ITS.

    Pulled the plugs before yesterday's race and 1-3 were lean. 4-6 were fine. I will pull them when I get home today.

    The radiator and cap were new last year. It's a 3-row from Champion. I used it last year and it kept the engine plenty cool.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Ideas:

    -Losing coolant? But not to the overflow? Do a leak down test for sure. Is one cylinder disposing of the coolant due to a HG failure and causing the mis-fire? Plugs might be a clue if one looks different than the rest.

    -Bad hoses, ie collapsed lower hose on the suction side.

    -Front cover damage in the impeller area causing poor pump performance. Check for chips and cavitation caused pock marks in the impeller housing area.

    -If using a thermostat, take it out and see if problem changes/improves.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

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    I didn't check the timing after swapping the MSD. I assumed that timing wouldn't change but I plan to check that tonight.

    I haven't done a pressure test but all the coolant hoses were pressurized when the engine was warm.

    I started Saturday with aa themostat but removed it for Sunday.

    I'll pull the plugs tonight and do a cold and warm compression test. I have a new leakdown tester that I can learn to use.

    Thanks for all the ideas guys!

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

  8. #8
    Registered User cbuczesk's Avatar
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    It looks like I found the problem. Here are my compression numbers from a cold engine: 157, 163, 175, 175, 165 183

    I never saw any smoke from the exhaust and it didn't smell like coolant. If it burned the coolant it didn't burn much of it because there was very little missing from the radiator.

    Now I have to figure out what caused the head gasket fail. I'm assuming that's what happened.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Nova Scotia,Canada,Earth Blue's Avatar
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    High RPM spark consistency is also affected by the meshing of the distributor drive spindle with the crank gear. There are combinations of steel and brass that are supposed to be better than stock.... I read this it in one of the datsun racing or datsun engine rebuild books.

    Maybe sunken brass seats or a valve adjust is the reason for the variance in compression.... did you baseline it after the rebuild?
    Last edited by Blue; 07-15-2013 at 06:38 PM.
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    Quote Originally Posted by cbuczesk View Post
    It looks like I found the problem. Here are my compression numbers from a cold engine: 157, 163, 175, 175, 165 183
    I only suggested the head gasket because some of the signs fit, but the signs also fit some of the other suggestions, like a collapsing hose, along with an ignition problem, for example. Those pressure numbers sure don't look good though.

    You have so many cars, and you're building your own engines, so I'm sure you know how to get good test numbers. Since it's so new and has few miles, I wonder if re-torquing the head bolts could save it? Not likely, but a re-torque would tell you if any of the bolts were loose, before you removed them to work on the gasket. If you find loose bolts, at least you'll have a possibility for the cause.
    1976 280Z, with some minor modifications

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    I had a bad HG and my numbers looked better then that, so not sure that tells all.
    The tester kit I suggested from Autozone(freebie borrowed tool) plugs into the radiator instead of the cap. You run the engine and see if the pressure rises above cap pressure. If it does, start pulling plug wires one at a time to try and diffuse the pressure. When the pressure stops rising, you found where your problem is. My symptoms were very subtle, never overheated, but I wasn't racing either. It just didn't run right, like a miss.
    That was a felpro gasket I believe, and it was giving out around #3. I'm running a Nismo gasket now.

    I also haven't read where you checked valve lash.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    At 6500 RPM's the thing that usually goes wrong is a valve starts floating. I'd pull your springs and check them all; you may have a weak one.

    As for overheating, sorry, we don't provide magic bullets here on ClassicZ but there are any number of overheating threads you can read and learn from, including this one:

    http://www.classiczcars.com/forums/h...mperature.html

    I believe that once one understands the THEORY of overheating finding the mechanical cause is fairly straighforward.

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    Registered User cbuczesk's Avatar
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    I didn't have time for a baseline after I built the engine. The head has new seats and guides and the valve springs were tested. I adjusted the valves last week before the race. I checked the head bolts and they were tight.

    I think what appeared to be a lean condition on the front 3 plugs was actually the blown head gasket. I'll pull it this week and check it for straightness. It's going to be a busy couple weeks. I also have to pull the transmission and fix a broken roll pin on 3rd gear. The joys of owning a race car! Thanks for all the help guys!

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Registered User LeonV's Avatar
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    Quote Originally Posted by Wade Nelson View Post
    At 6500 RPM's the thing that usually goes wrong is a valve starts floating.
    Do you have any corroborating data or calculations to even remotely prove this, or is the statement pure conjecture?
    2/74 260Z

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    Registered User madkaw's Avatar
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    Wade,
    Are you serious?
    "Here at ClassicZ , we don't have magic bullets" -
    --ummm, I hope you aren't speaking on my behalf with such a pompous statement.

    So I guess your car never sees redline for fear of floating valves?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Chuck

    Could you be kind enough to keep us posted on what you find, maybe post some pictures. I would really like to see that cause of that overheating if it is actually the HG. As for redlines, all cars have them and they vary depending on too many factors to list. I personally don't like approaching them - I have a hard limiter at 6500 - but I've seen Z's hit 8k before without an issue. It all depends.

    Thanks
    Jan
    1976 280Z
    HLS30288273

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    Registered User cbuczesk's Avatar
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    Jan,

    I'll post pics when I get back out to the garage. Tue-Thu nights are filled with softball playoffs, volleyball, groceries, mowing, etc. I'm off Friday so I'll work on it then and post some pictures. I'm curious to see the head gasket too.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

  18. #18
    '72 240Z(G) 3.2L
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    So our 300 hp L28 with the 44mm carbs, pistons and other nice bits from the original BSR 240 running at 13:1 CR on 110 fuel ran hot from day one.

    The 240 did real well at the VRG event last year taking 1st, 2nd (overheating on the last lap), and DNF (first lap overheated).

    We changed out radiators, hoses, timing, a new head gasket, reconfigured the cooling system, replaced the BSR E31 head, etc.

    Little bubbles became much bigger bubbles once the throttle was blipped. Current thought is a small cylinder wall crack.



    Since the only thing that didn't get changed was the block and we started to get bubbles at idle and then big bubbles at WOT.

    We figured cracked block.

    Out came the engine and all the usable stuff (8-gal custom oil pan, diesel water pump and custom front cover, a real BSR valve cover, the huey tranny oil cooler
    if a little knowledge can make you dangerous, I'm a little dangerous

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    Registered User cbuczesk's Avatar
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    Wow. I sure hope I don't have a cracked block. I had the radiator cap off while the engine ran so I could see if the coolant was flowing through the radiator. It was. I didn't notice any bubbles though. I'm anxious to get the head off this Friday.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Registered User cbuczesk's Avatar
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    I pulled the head today. Everything looks good. I was hoping to see something that didn't look right. I have another E31 head that I just picked up from the machine shop. I think I'll put it on the block and get the old head pressure checked. What do you guys think?

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Hmm that interesting

    How do the valves look on the head? Any of them burned (really lean)? How did the pistons look?

    Jan
    1976 280Z
    HLS30288273

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    Registered User cbuczesk's Avatar
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    Valves and pistons look fine...everything looks fine. #1 and #2 are a little lighter in color than #3-6 but everything looks good.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    HG fire rings all look solid, no blow by anywhere?
    On my HG , it showed up more as a discoloration of the fire ring.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by cbuczesk View Post
    Valves and pistons look fine...everything looks fine. #1 and #2 are a little lighter in color than #3-6 but everything looks good.

    Chuck
    Lighter as in cleaner then the other pistons?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Diesel water pump. Is it better than the normal petrol pump.

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    Registered User cbuczesk's Avatar
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    Lighter as in cleaner. Everything about the head gasket looks fine. I went over everything for a long time with a flashlight and magnifying lens. I checked the head with a straight edge and it looks good. Whew! I think I'll prep the other head and have this one checked by the machine shop.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    What HG were you using? Do you run just water or Glycol ?
    I asked about the cleaner pistons because maybe some water was steam cleaning your pistons . It wouldn't take much of anything to pressurize the coolant system.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Registered User cbuczesk's Avatar
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    I used a full FelPro kit. I've never had a problem with FelPro. I ran water for the first weekend of use and a mix last time. I think there was a little steam cleaning the pistons and chambers. I think it was a very small leak and the temp dropped to normal under normal loads. When I did easy laps and the cool down lap the temp dropped to normal. But after 2-3 hard laps it was 240 degrees.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Any chance the head had some warpage? Was it machined to flatness before building, or maybe at the high end of the warp limits and used as-is?

    I've never rebuilt an engine but I'm curious. I have a warped head in the garage and wonder how much is too much and what the effects are.
    1976 280Z, with some minor modifications

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    Just curious of your engine specs as far as CR?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Registered User cbuczesk's Avatar
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    The head was on an engine that I removed from a car about 20 years ago. I had the head resurfaced just to clean it and make sure it's straight. We aren't allowed to shave it to raise compression for IT racing. I have new 20 over pistons installed so compression is about 9:1...stock. Everything is stock except for +20 pistons, Hooker header, exhaust, semi-custom air cleaner, oil cooler, Taylor plug wires and MSD 6.

    Chuck
    East Coast Z Nationals held at the Carlisle Import & Kit Nationals - May 16-18, 2014 Carlisle, PA
    www.carlisleevents.com/events/import
    1969 240Z #390
    1971 Fairlady Z
    1971 240Z parts car
    1972 240Z ITS race car
    1972 240Z turbo
    1974 260Z turbo
    1975 280Z my first car
    1978 620 King Cab

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    Registered User madkaw's Avatar
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    Personally I would spend the money on a Nismo gasket. They are pricey, but I think it's worth it. 125$ at Courtesy Nissan.
    Last edited by madkaw; 07-20-2013 at 10:40 AM.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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