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| Overheating | Rating: 
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| Posted: 06-27-2005 03:36 pm |
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1st Post |
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Mitch Ware Member 
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Last year #19670 ran cool even on the hottest days. Then it was put away for the winter. Before taking it out of storage, I drained the anti-freeze and replaced it with a 50/50 mixture of distilled water and prestone green. I have noticed that the temperature guage has been reading higher on the average this year than it did last year (the first year that the car was back on the road). Yesterday, on a very warm day, the temp guage went right up to the red after about 3 miles. I nursed the car back home and let it idle in the driveway, spraying water on the front of the radiator. this brought the temp back down to where it has been reading since I took it out of storage this spring (just to the bad side of the middle). I checked the coolant level, it is fine. The thermostat seems to be opening since the radiator gets hot. The water seems to be circulating, since spraying water on the radiator cools the engine temp. The coolant level is where it is supposed to be. Both the radiator cap and the thermostat are one year old. The coolant is fresh. I blew out the radiator fins with compressed air to make sure the air was flowing, it is. I have had a shroud around the fan since I restored the car. So what gives? any ideas would be appreciated Mitch Ware 1974 JH-5 #111119670 1971 TR-6 #CC66950LO
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| Posted: 06-27-2005 05:16 pm |
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2nd Post |
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Greg Fletcher Administrator 
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I would change the thermostat before I do anything else, as that sounds like an issue in this case. They can go bad anytime. You might look for one of those FailSafe thermostats- they fail in the open position and avoid the problems of sudden overheating that convensional thermostat can cause.
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| Posted: 06-27-2005 09:49 pm |
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3rd Post |
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Judson Manning Member 
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Mitch, You might want to install an aftermaket water temp gauge. The stock water and fuel gauge run off a 9V regulator that is prone to failure resulting in higher temp readings when everything is actually fine. Judson
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| Posted: 06-28-2005 01:21 am |
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4th Post |
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Mark Rosenbaum Member 
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Before changing the thermostat, I'd check two things: 1. Correctly operating temp gauge. With a coolant temp at a measured 80^ to 85^C (the normal operating temperature for the stock 82^C thermostat), the gauge should read mid-range or a needle's width to the right. However, as Judson notes, the actual reading depends greatly on the voltage stabilizer. (a) If the stabilizer fails in the 'always off' mode the temp gauge and fuel gauge will not work. (b) If the stabilizer fails in the 'always on' mode the temp gauge will appear to operate normally at first, but will rise to, or into, the red zone as soon as the engine reaches operating temperature; simultaneously, the fuel gauge will indicate far more fuel than is actually present (which is hard to detect if the tank is full). This seems to correlate with your car's symptoms. 2. Presence of coolant in the heater core -- air can be trapped there and later transfer to the engine, causing localized internal overheating. Your car is late enough that it may have a vacuum operated valve in the hose to the heater, and these are notoriously unreliable. Of course, as Greg notes, a thermostat can fail at any time and without warning. Worse yet, they sometimes fail intermittently and seriously confuse the issue. Last edited on 06-28-2005 01:22 am by Mark Rosenbaum |
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| Posted: 06-28-2005 03:24 am |
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5th Post |
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Mitch Ware Member
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My car does indeed have the vacuum operated heater valve. The fuel guage seems to be working accurately, but I will keep a closer eye on it. One of the things that puzzles me is how quickly the engine reaches operating temperature. According to the guage, it only takes about 1 mile of driving. Of course, it has been in the mid-90's here in upstate NY this weekend, so that may be a contributing factor. I went ahead and ordered a new thermostat and gasket, might as well try the easy fix first. As always, thanks for the suggestions and insight. Mitch Ware 1974 Jensen Healey JH5 #111119670 1971 Triumph TR6 #CC66950LO Last edited on 06-28-2005 07:20 pm by Mitch Ware |
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| Posted: 06-28-2005 03:36 pm |
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6th Post |
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Mark Rosenbaum Member
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If I start my car when the air temp is 85^F, and let it idle on the driveway, it takes about seven minutes for the engine to reach the point where the thermostat opens -- in my case, a measured 185^F. This works out to a warmup rate of about 14^F per minute. It's my understanding that this is pretty typical of a 907 engine. So, if your car's temp gauge indicates overheating within a minute or two of starting from an overnight rest, I'd be very suspicious of the temp gauge. Of course, you could have a bad gauge (or voltage stabilizer), and a bad thermostat....
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| Posted: 10-16-2005 10:09 pm |
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7th Post |
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Rory Clark Member
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I wanted to revisit this temp thing. Finally got my 73 on the road. (There are still things to do with Carb adj and recheck of timing) My car runs just a few points below the red line on temp ga. and stays there (50-miles of driving). I firmly believe it is running to hot So, what other things can cause the motor to run hot??? I know: 1) Thermostat 2) Air pocket in system. 3) Water pump 4) Others??? Rory
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| Posted: 10-16-2005 11:03 pm |
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8th Post |
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Jensen Healey Super Moderator 
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Running lean 2 core radiator sediment or corrosion in block bad valves clogged oil cooler wrong timing excessive antifreeze mix no fan shroud cheap plastic fan etc. etc. etc. In other words, Everything! Last edited on 10-16-2005 11:03 pm by Jensen Healey |
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| Posted: 10-17-2005 01:50 pm |
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9th Post |
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Mitch Ware Member
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I eventually traced mine down to a failing voltage stabilizer. My fuel gauge and temperature gauge fluctuate in sync. It is on my list for things to address this winter when the car is in storage. Mitch Ware 1974 JH-5 #111119670 1971 TR-6 #CC66950LO
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| Posted: 10-17-2005 06:39 pm |
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10th Post |
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Judson Manning Member
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Actually, one thing we didn't mention is excessive blow-by. If your piston rings are shot, you'll have excessive oil temp which will cause the water temp to rise. The problem is similar to a blown head gasket where spent combustion gasses leak into the water jacket. However, a blown head gasket typically exhibits white smoke from the exhaust, as it's hard to keep pressurized water out of the combustion chamber during intake at idle (lots of vacuum). The excessive blow-by problem is hard to diagnose until you install an oil temp gauge.
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| Posted: 10-17-2005 07:03 pm |
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11th Post |
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Greg Fletcher Administrator
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Blow-by is unpleasant. I've experienced hotter temps with three cylinders that had marginal compression and one cylinder that was quite bad- the three were doing the work of all four. In that instance it was bad rings in the number four cylinder and was easy to see from the compression gauge since it was so far gone. Perhaps worth mentioning- the club store has been selling a lot of remanufactured water pumps and I've been noticing many of the cores I get back are not to spec- often the impellors are way off and not close enough to the housing. Whoever rebuilt the pumps last, didn't read the Lotus clearance recommendations in the manual. Some of these are so far off that they could conceivably effect the cooling (for the worse) on the engine, so you really need to look at everything at engine rebuild time or if you're getting a car recently that has issues.
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| Posted: 10-17-2005 10:29 pm |
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12th Post |
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Rory Clark Member
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One interesting thing that I have noticed is that the hose that runs on top of the motor to the thermostat is flattened when the car is cold once it gets up to temp and I assume the thermostat is open it goes to a full round. It is like as the motor cools down a vacuum is formed in the cooling system. Rory
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| Posted: 10-17-2005 11:23 pm |
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13th Post |
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Mark Rosenbaum Member
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Haven't noticed that sort of hose change in my car, either with the old hose or its replacment. Both were the Gates hoses that Delta provides, with the metal coil inside. I wonder if there's some relationship between what Rory reports and the (probably) defective hoses mentioned in the thread at the link below. http://www.jensenhealey.com/forums/view_topic.php?id=336&forum_id=3
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| Posted: 10-18-2005 01:35 am |
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14th Post |
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Rory Clark Member
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I will take a picture of it and post. With all the parts that I replaced, the hose are not among them. Now since the car is down for the blown exaust header gasket I guess I will order the hoses from Delta with the gasket. Rory 73-JH Here is the picture of the Flat Manifold Hose. Like I said once the car gets up to temp it takes the round shape Attachment: Rad hose flat.jpg (Downloaded 89 times) Last edited on 10-18-2005 04:05 pm by Rory Clark |
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| Posted: 11-10-2005 01:30 am |
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15th Post |
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LambandAndy Member 
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Well I drove 15223 to work today and actually arrived with the same amount of coolant that I left home with. For anyone buying a JH with unknown history I thought that I would relate some of our experience. After looking around for something a little more economical to drive than my 1977 F150 4X4 my wife suggested a Jensen Healey since I used to own one way back when. A search on the internet found a JH advertised on the JHPS website in South Carolina. A reverse look-up on the phone number showed it to be in Charleston, about 250 miles away. So after a couple of days and a couple of phone calls my wife, Lamb, and I piled on my trusty old Suzuki and headed for Charleston. The car was pretty much as the seller had told me and needed a new floor and a new top, but only had 40,000 miles on it. The title, issued in 1993, showed that the car had only covered ten miles in the last twelve years, so I believe this milage to be genuine. The seller also informed me that he had installed a new thermostat, new water temperature sender and had rebuilt the water pump. So a deal was struck and we set out for home, with Lamb driving the JH and me on the bike. Ten miles up the road Lamb pulls over with the temperature gauge in the red. Although indicating hot, the engine did not seem hot, not boiling and didn't have that 'hot smell'. So we let it cool down for a few minutes then carried on to the next gas station to investigate. After prodding around under the hood for a while I thought that maybe the guy had put neat antifreeze in, so drained some out and refilled with water. We were also getting very suspicious of the temp gauge. So we went on for a while and stopped at an auto parts store to see if they sold anything that we could verify the temperature with. After the third store we gave up on this but by then the car, and the day, had cooled off some. So to cut a long story short we made it home in fits and starts. Here are some of the cooling problems/corrective actions taken so far. 1. Installed correct thermostat (PO's new thermostat did not have the "bypass disc"). 2. Flushed cooling system. 3. Installed new hoses. 4. After reading e-mail on JHPS, noted fuel gauge and temp gauge reading high. Removed instrument panel and checked voltage stabilizer. Input was battery voltage and output seemed to fluctuate. Scratched head for a while, reassembled, and now fuel gauge and temp gauge seem to be working normally. (Bad connection?) 5. Removed piece of "spring" from previously installed flex hose from thermostat housing. 5. Removed water pump, pressed impeller on to correct clearance and reinstalled. 6. Removed radiator, re-soldered nipple for outlet to water pump and reinstalled. 7. Drove to work today and temp gauge remained at 3/4 scale. I am still suspicious of temp sender installed by PO. Infrared thermometer shows about 200F on the thermostat housing which seems about right to me. Is there a way to positively ID if this is the right sender? I cannot find any part numbers or Smith logo on it. Other work completed has been general engine tuning, changing of all fluids, correct installation of vacuum hoses (thanks Mark), replaced cam belt, replaced top (Bought a "cheapie" top from M & T Manufacturing for $177. I thought that it fitted well. Can put up pics if anyone is interested). Working on floor pan replacement. Thats it for now, Andy #15223
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| Posted: 11-10-2005 03:04 am |
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16th Post |
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John Finch Member
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Andy, I'd be interested in a pix and your opinion so far of the replacement top you purchased. Mine just ripped so I am forced into a replacement for spring driving in Minnesota. Thanks John
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| Posted: 11-10-2005 09:46 am |
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17th Post |
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Harkes Member 
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Hi Rory, give us an update on how your car is doing now... Did you tackle the hot temp? The JH with decent compression and original 2 core radiator and original thermostat should be running in the middle of the temp. gauge and could go up when stuck in traffic. have you measure the actual temp whilst the temp gauge dial is up high? My old 2.0L engine ran fine eventhough it consumed quite a bit of oil!! You could indeed switch to a different (lower temp) thermostat and add water wetter to your cooling system. This is great stuff. Also check all hoses if there is nothing clogged inside. For instance my heater hose..the long thin hose that runs from heater box via bypass to the waterpump was fully closed up..!! not a good thing. Saw the picture of your manifold hose to the waterpump. I'd swap that one AND the upper and lower radiator hoses for the Gates hoses that are wire reinforced. They are only 15$ a piece at DMS. I'm most likely going for blue silicone wired reinforced hoses. they cope with heat very well, are very strong but mostly...look good. erik
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| Posted: 11-10-2005 06:34 pm |
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18th Post |
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LambandAndy Member
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Ok, so it looks like I crowed to soon. 15223 blew out coolant on the way home, but temp gauge never went over 3/4 (about 200F). My thinking is: Not overheating + blowing out coolant = blown head gasket (or worse) Anyone got any other ideas before I tear the head off? Andy #15223
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| Posted: 11-11-2005 06:56 pm |
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19th Post |
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Rory Clark Member
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Eric, I have been to the Netherland many times what a beautiful Country (after you get out of Ampsterdam of course) My heat problem could be just a bad sender (but I do not think so) On a normal day here 29-35c it would just slowly climb to the 7/8 mark and stay there I could be driving at 55 or 110km (35-70mph) and it made no change. Bit Boy you open the hood and it sure seemed hot. Since I blew the exaust (Header Gasket) which is a no brainer to repair Just a super Pain in the A _ _. I did just as you said bought new upper/Lower hoses Plus the 74c thermostat (Jaguar PT# C28067). I have not installed hoses/thermostat (or fixed the Gasket) yet. But I will be VERY interested if this works on reducing the heat. Best Rory
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| Posted: 11-11-2005 07:10 pm |
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20th Post |
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Brett Gibson JH5 20497 Member
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Rory, getting back to your flattened hose when cold, it should'nt do that, so why is it, maybe the system becomes under vacumn, like when you fill a water bottle with warm water and then seal it and put it in the cold, you come back later and it all shrunk up, the only way your car can do that is if the Rad. cap doesnt allow the siphoning back from the overflow bottle. Just a thought.............. Brett.
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