MHKflyer52 Posted May 9, 2008 Share Posted May 9, 2008 Well here is my problem with my 7. My car has developed an overheating problem the last two times I have had it out and taken it above 65mph (freeway speeds) for any period of time and I can not seem to find out what is wrong with it. A little history about the car. Rebuilt engine 3 yrs ago (MGB 1800cc) and have driven it a lot since then. Ok I know it is an MGB engine. Oil pressure stays at 30lbs at idle once warm and maintains close to 60 lbs when running hard and 45 to 50 while running around. Good even compression on all cylinders. No evidence of water in the oil or oil in the water. New radiator when building the car 3 yrs ago. Have flushed the system every year as preventative maintance. Auto-X numerous times no problems and lots of hard spirited driving in between. Never over heated before the last Auto-X. Car puked about a quart of coolant at the auto-x after the second run and I replenished the coolant after it cool down. Temp prior to boil over was constant 185 degrees. Temp reached 220 degrees during the first run and cool down to normal after first run and did not boil over or at least over flow my overflow tank. Second run temp climbed to 195 degrees after stat up and stayed their through the run but at the end of the run climbed to about 225 and then cooled down to just under 200 degrees with the car idling, this is when I noticed that my overflow tank was leaking coolant in the parking area. Third run after starting the car temp climbed to 200 degrees and then pegged my gauge after the run and deposited a large quantity of coolant in my trailer. Next day serviced radiator and let car sit at idle with no overheating and temp stable at about 200 degrees by my gauge in the dash without the fan being turned on. Pulled thermostat and replaced with new one that is for 185 degrees, flushed system and checked for water in the oil (negative) and test drove around the neighbor hood with no problems, temp stayed at 185 degrees. Next day I was going to drive it into the office and headed out watching for any sign of overheating, everything seemed good till I entered the freeway and got up to the speed of the traffic (about 75 mph) noticed the temp climbing through 200 degrees so I returned home and switched cars. Later that evening I drove the car around the neighbor hood with out any over heating (temp stayed at just over 185) and the coolant level looked to be correct after returning to the garage. Today backed the 7 out of the garage and went for a nice little ride through town without any overheating (temp stayed at about 185 degrees) even in stop and go traffic in town. Headed out of town to go cruse the hills and jumped onto the freeway for about two exits or about 3 miles at speed and the temp when up between 200 and 210 so I departed the highway and hit the side roads to see if it would cool down which it did at first (about 195) so I headed for home. About two blocks from the house the temp started to climb and by the time I was able to get into the drive and put a garden hose on the radiator face it was over flowing my spill tank (temp reached 220) again and finally started to cool back down while idling and the garden hose running on the front of the radiator. Anyone have any ideas as to what is wrong before I pull the head to check for cracks. :7frog: Link to comment Share on other sites More sharing options...
slngsht Posted May 9, 2008 Share Posted May 9, 2008 interesting... just starting out with simple things, have you made sure the water pump belt has proper tension? is there a procedure for bleeding the air out of the system? Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 9, 2008 Author Share Posted May 9, 2008 Hi Mazda, Yes I have checked the fan belt and even bleed the system after replacing the thermostat and flushing of the system even replace the radiator cap with a new one. Link to comment Share on other sites More sharing options...
SkinnyG Posted May 9, 2008 Share Posted May 9, 2008 Have you checked for a leaking or blown headgasket? I would put money on this. Combustion gasses/temperature getting into the coolant at speed cannot be dissipated by ANY cooling system - yet the engine will run nice and cool at idle. Pull the rad cap off with the engine idling. As it heats up and the thermostat opens, you may see a bazillion tiny bubbles frothing through the coolant - probably overflowing out the rad filler - the head gasket is your culprit. Failing this, many shops have a dye they can use to test for the existence of combustion gasses in your coolant. G Link to comment Share on other sites More sharing options...
11Budlite Posted May 9, 2008 Share Posted May 9, 2008 I've got a '64 MGB and I was thinking the same thing as SkinnyG... Bruce :7drive: Link to comment Share on other sites More sharing options...
tnttim Posted May 9, 2008 Share Posted May 9, 2008 Failing this, many shops have a dye they can use to test for the existence of combustion gasses in your coolant. G They also have an adapter with a pressure gauge on it that they put on the radiator cap they put a few pounds on it and then let it sit. One shade tree way you MAY be able to tell is to pull the spark plugs and look into the cylinders. The color of your sparkplug may be different than the others and all the carbon will be blown off the top of your piston. (it will cleanre thanthe others). If it is a bad enough leak you may actually see water on the top of the piston if you let it sit after heating it up. I did have 2.3L Ford that i messed the ignition timing up and it overheated alot till I figured it out, but it also kinda ran funny. Tim Link to comment Share on other sites More sharing options...
southwind25 Posted May 9, 2008 Share Posted May 9, 2008 Do a leak down test instead of a compression test? And this is way obscure..but how old is the water pump?, meaning i have heard (urban myth?) that on occasion the pump impellor may come loose on the shaft then it sli[ps a bit under higher revs-hydraulic pressure.. especially if it is an aftermarket pump with the sheet metal pressed vanes. Another trick some guys do on engines that live in higher revs, is they have a larger dia pump pully to slow down the pump a bit. i had a 70's MGB some years back...with a constant overheating problem, but it turned out to be the funky MGB radiator. Link to comment Share on other sites More sharing options...
WestTexasS2K Posted May 9, 2008 Share Posted May 9, 2008 Southwind that was going to be my suggestion. I would check the water pump. I have seen impellers come completely off the shaft. If you can pull the pump and look at it. Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 9, 2008 Author Share Posted May 9, 2008 Southwind that was going to be my suggestion. I would check the water pump. I have seen impellers come completely off the shaft. If you can pull the pump and look at it. I ordered a new water pump last night and it should be at home when I get their this evening. I have also heard that the impeller on the MGB water pump can erode or even come off the shaft and still work under low RPM's but not at the higher rev's so that is the next step before pulling the head. I have checked for the radiator with the cap off to see if I had bubbles in the coolant while the engine was running and did not see any. I also checked the plugs to see if their was any dis-color and found them all to be very close to the same goldern tan color. Thanks for the ideas and I will post what I find tonight after I pull the water pump. Note; Just sitting here thinking about when I rebuilt the engine I do not think I replaced the water pump but will have to check my records but I am perty sure I did not due to it looking in good shape at that time, boy I hope it is the cause and not a cracked head or blown head gasket or some unseen blockage in the coolent system. Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 11, 2008 Author Share Posted May 11, 2008 Thanks for the ideas and I will post what I find tonight after I pull the water pump. Well replaced the old water pump with a brand new water pump. The old pump has a little more gap between the housing and the impeller but other than that they look the same. http://picasaweb.google.com/MHKflyer52/OldAndNewWaterPump Put the new pump in and and also replaced the themostat with a new one to be on the safe side (they are cheep and someone told me to try a 165 degree), filled the radiator and engine with coolant and insured that their was no air in the system. Started it up and let it warm up, it seemed to level out at about 190 degrees so I decided to go for a spin. Looks like the head needs to come off and be replaced as the temp stayed at about 190 to 195 around the neighbor hood but as soon as I was able to get up over 55mph the temp started to climb so I headed back to the garage. By the time I was able to get back to my garage the temp had climbed up to just over 220 degrees and was not showing any sign of cooling off. :banghead: :cuss: I guess the head needs to come off and be replaced. :banghead: Link to comment Share on other sites More sharing options...
slomove Posted May 11, 2008 Share Posted May 11, 2008 Sorry to hear that. But before you take radical steps you might want to measure the in and out temperatures of the engine for further clues. Since you probably don't have remote lab thermometers you could try 2 remote BBQ thermometers with the sensing tips taped to the coolant hoses (and insulated with some foam). Something is not right here (doh...) did you check if the radiator may be gummed up? Also just for fun you could completely remove the thermostat and see if that makes any difference. Gert Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 11, 2008 Author Share Posted May 11, 2008 Sorry to hear that. But before you take radical steps you might want to measure the in and out temperatures of the engine for further clues. Since you probably don't have remote lab thermometers you could try 2 remote BBQ thermometers with the sensing tips taped to the coolant hoses (and insulated with some foam). Something is not right here (doh...) did you check if the radiator may be gummed up? Also just for fun you could completely remove the thermostat and see if that makes any difference. Gert Hi Gert, I have actualy removed the radiator and presure flushed it to make sure that it is not pluged or gumed up and I have also tried running the motor with out the thermostat and the only differance is it overheats about twice as fast. One friend of mine that is into british car restoration in a big way (Wellwood Auto Restoration, Inc.) has sugested that I most likely have a crack in the head in one of the exhaust ports and as the engine heats up under higher RPM's and greater pressures then lets the exhaust due two things, one is that it can suck the coolant out of the water jacket and vaporize it so that it dose not show up in the short exhaust system that I have on my car. The other thing that he has said it could due is presurize the water jacket and cause the coolant to get superheated and not be able to cool down even with the radiator and the fan and the thermostat and water pump all working correctly. This is a good posability as my head has been ported and that makes the walls a lot thinner and prone to cracks and besides the head on my engine is 30 plus years old and I am the one who rebuilt it and did the porting back when I rebuilt the motor 3 years ago so I am thinking that is most likely the problem a crack in the head in one of the exhaust ports. Thanks for the sugestion of useing some thermal cuple probes to check the inlet an outlet temps as that is about the only thing that I have not done and will due that tommorow as I due have a Fluke Meter and at least one thermal couple that I can tape to the inlet an outlet of the engines water jacket. I due know that I will also be replacing my hoses as I noticed that they were swelling a lot under the presures that they have been seeing even though they are holding for now they sure have been stressed by excesive heat and pressure. I will post what I find as I progress with solving this problem. Just have to get one of the other cars out if I want to go for a ride. Again thanks for the sugestions as they always help in trouble shooting. Link to comment Share on other sites More sharing options...
lowflyer Posted May 11, 2008 Share Posted May 11, 2008 The fact that you said your hoses are swelling up due to pressure may be an indicator that you have too high a pressure radiator cap in place. If the cap doesn't open, or opens at too high a pressure it can keep the water from pushing out and causing a slow down in water flow through the radiator. You may also have air in the coolant system. On our Stalkers this is very common due to the height of the rad vs. the top of the thermostat housing. Try jacking the nose of the car up as far as you can, block off the radiator and run the car until it's up to around 225/230. Let it cool down and see if it draws fluid back from the overflow tank. You may even see air bubbles in the tank after it runs for a while. In addition to all the other things mentioned about cylinder heads and such, look at the simple things first. You mentioned that you rebuilt the engine, is there a possibility that when you reinstalled everything you may have turned the engine fan around on the water pump? Don't ask me how I know this, but this little "oops" will cause overheating at speed! Good luck. Link to comment Share on other sites More sharing options...
lowflyer Posted May 11, 2008 Share Posted May 11, 2008 Oh yeh, don't forget to consider that your gauge is bad !!!! Don't ask how I know that one either. Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 11, 2008 Author Share Posted May 11, 2008 Oh yeh, don't forget to consider that your gauge is bad !!!! Don't ask how I know that one either. Hi Lowflyer, Thanks for the tip on the pressure cap. I have actually replaced the old cap thinking that might be the a problem due to it being weakend from time and use. I have had the same result with both the new and the old caps, as for the fan my engine has none as it uses an electric one mounted on the radiator and I have checked it and it is working as it is suspost too. As for air in the system I actualy have though that might be a problem but have eliminated that early in the trouble shooting process. Thanks for the input as it keeps me rethinking what I have tried and provides me with other ideas to try. :7frog: Link to comment Share on other sites More sharing options...
slomove Posted May 11, 2008 Share Posted May 11, 2008 .........is there a possibility that when you reinstalled everything you may have turned the engine fan around on the water pump? Don't ask me how I know this, but this little "oops" will cause overheating at speed!...... Good point. Kind of unlikely since you built it yourself but with the old Ford Zetec ZX1 that I have many Seven installs route the serpentine belt the "wrong way" around the water pump pulley to keep the installation compact. That means you can not use the US Ford Contour water pump but need to get a Ford Escort or Fiesta pump from Europe for proper spin direction. But I have no idea if that could even happen with the MGB engine. Gert Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 11, 2008 Author Share Posted May 11, 2008 Good point. Kind of unlikely since you built it yourself but with the old Ford Zetec ZX1 that I have many Seven installs route the serpentine belt the "wrong way" around the water pump pulley to keep the installation compact. That means you can not use the US Ford Contour water pump but need to get a Ford Escort or Fiesta pump from Europe for proper spin direction. But I have no idea if that could even happen with the MGB engine. Gert Hi Gert, Good point but with the MG engine the altenator and water pump are small so no relocation is necessary and the one belt drive only goes on one way and the altenator is used to keep tension on the belt. Thanks for the thought though. Everything at this point looks like a crack in the head so later today or tommorow it is going to come off and be inspected. Now I just have to deside on a cross flow head or go with a stock head as they are about the same price for each and the cross flow head means changes, mainly new carbs and a new hood. I am seriously considering looking at a V6 as I can get a low milage engine and trans for what a new head is going to cost at this point but for now it looks like the head is coming off and then I will know better as to what direction I will be going. :7frog: Link to comment Share on other sites More sharing options...
scannon Posted May 11, 2008 Share Posted May 11, 2008 as for the fan my engine has none as it uses an electric one mounted on the radiator and I have checked it and it is working as it is suspost too. Did you just watch to see if the fan came on or did you put your hand behind it and feel the air flowing in the correct direction? Some electric fans will run in reverse if you reverse the leads. BTDT, with similar symptoms to yours. Everything was fine until the engine got hot enough to turn on the fans. Skip Link to comment Share on other sites More sharing options...
MHKflyer52 Posted May 11, 2008 Author Share Posted May 11, 2008 Did you just watch to see if the fan came on or did you put your hand behind it and feel the air flowing in the correct direction? Some electric fans will run in reverse if you reverse the leads. BTDT, with similar symptoms to yours. Everything was fine until the engine got hot enough to turn on the fans. Skip Hi Skip, First thing I checked after checking to see if the fan belt that drives the water pump was not missing. Thanks for the input. :7frog: Link to comment Share on other sites More sharing options...
slngsht Posted May 11, 2008 Share Posted May 11, 2008 I am seriously considering looking at a V6 as I can get a low milage engine and trans for what a new head is going to cost at this point but for now it looks like the head is coming off and then I will know better as to what direction I will be going. :7frog: V6 is too much engine for a seven Link to comment Share on other sites More sharing options...
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