2.25 petrol overheating

[Jdnewberry]

I have been fighting an overheating problem and need some help from you guys.

I have a 3MB 2.25 petrol with 27,000 miles that over heats at highway speeds. The head has been shaved from 7:1 compression to 8:1 compression and converted to unleaded. The block has been flushed, it has a new 4-core radiator from Rovers North, new distributor, new plugs, new carb, etc... But it still overheats.

I have been over everything I can think of and I'm out of ideas. The curious part of the problem is the temp in the radiator. The coolant gets to about 210 deg after a short run at highway speeds and will be about 10 deg cooler at the bottom. The radiator is evenly warm from side to side, so it isn't blocked. The water pump is perfect, the thermostat works correctly, new radiator shroud, hoses are fine, the timing is set per specs, carb has the proper jets, but it still runs hot at speed. After a short drive at 35-40 mph, temp drops back down.

I'm lucky though. My mechanic specializes in classic European cars, graduated with honors from MIT, and loves to give free advice because it keeps his work load down.

He said something that confused me today. He said he thinks my radiator might be flowing to fast and not giving the coolant time to cool off. Is that possible? I've never heard of such a thing! If the coolant is spending less time in the radiator, wouldn't the time it's spending in the water jacket be proportionally less?

If the cooling system is not the issue, I'm out of ideas. I have run the timing everywhere from 12 deg BTDC to 6 deg ATDC, installed a new weber with new jets (165 main, 190 air corrector, 50 idle, 40 back bleed, 55 pump, F6 tube) gone 1 heat range cooler on the plugs and it still runs hot at speed. I have even changed the air corrector jet to 170 thinking that maybe it was running lean.

Any ideas on something I have missed? Is there any truth the radiator flowing too fast?

Thanks in advance.

[TravelinLight]

I cannot imagine a situation where the 2.25 with everything you have stated done would overheat.

Is the fan belt the correct one for your pulley and tight enough to spin as supposed to? The reason I ask is the issue that it is not circulating the fluid to be cooled properly? Is it slipping at higher RPMs.

Have you tried to run it without the thermostat to insure you are getting the proper flow? Even though it opens as expected I would run it without one for a trip or two to see if you can isolate?

[Jdnewberry]

The fan belt is tight and it is the correct 1050mm size. I know it's pumping at speed, because the temp in the radiator runs so high. I have not removed the thermostat yet, but since the the temp runs so high, I can't imagine it's restricting the flow.

I may try to run it without the thermostat tomorrow if the weather holds. It's been rainy here and my top is off!

[SafeAirOne]

Is your mixture too lean? Does it cool off if you enrich the mixture?

What temp rating is the installed thermostat?

[Jdnewberry]

I'm not sure about the mixture. I have asked about that, but I can't find anyone to test it for me. I do have the recommended jets for the 2.25 installed in the webber and have even gone down a size on the air corrector, but it didn't seem to make a difference.

I wonder though, because where the exhaust runs under the footwell, it'll roast your toes when your driving. I can't imagine that's normal.

The thermostat is the 74 deg and it opens early if anything. It seems to open about 70.

[darbsclt]

Silly question... but, you're sure that the thermostat installed is a "skirted" type.
I only ask because use of a non-skirted type, while appearing to function, won't channel the water properly for adequate cooling.

Cheers...

[Jdnewberry]

There's no such thing as a silly question. Yes, it is skirted. I picked it up from our hosts this spring when the weather warmed up.

[ignotus]

Where and how are you measuring the temp after running? So a 74 thermostat is equal to 165F, 100C=212F. Like darbsclt says make sure you have the correct stat ^^^^. Not sure but TeriAnn might have it on her website. http://www.expeditionlandrover.info/

[leafsprung]

A few things that would be helpful in diagnosis:

-an infrared thermometer would be helpful in determining your coolant temperature at various points in the system
-check your plug color for evidence of correct mixture (light brown ash)
-bubbles in coolant or coolant loss indicating a gasket failure or crack

[darbsclt]

I may try to run it without the thermostat tomorrow if the weather holds. It's been rainy here and my top is off!

Keep in mind... running the engine at temperature without a thermostat will simply cause the coolant to flow through the bypass port rather than the radiator (the 'stat skirt blocks this port when functioning properly). This can cause the engine to run hot.

As Ignotus referenced, Teriann has a nice write up HERE

[lumpydog]

Does your gas gauge work?

I ask because, if it doesn't, it may be that your voltage stabilizer is not working and feeding your temp gauge and gas gauge the wrong voltage... and causing both to be inaccurate. It's harder to tell something's wrong with the temp gauge, but the gas gauge - it's more obvious if it's off. If the gas gauge is not accurate, try swapping out the stabilizer.

Also, consider the temp sender... Mine recently bonked. I noticed it when, within a minute of starting the engine, the gauge showed the engine as mid gauge on the temperature gauge... Does it warm up at the expected rate?

Bottom line - maybe the engine temp is just fine... the gauge just isn't accurate due to bad voltage stabilizer, bad sender or... even a bad gauge.

[Jdnewberry]

Where and how are you measuring the temp after running? So a 74 thermostat is equal to 165F, 100C=212F. Like darbsclt says make sure you have the correct stat ^^^^. Not sure but TeriAnn might have it on her website. http://www.expeditionlandrover.info/

It is the correct stat. Temp is measured two ways: first, I found a nifty radiator cap at the parts store that has a thermometer built in and second, I have an infrared thermometer. The rad cap is graduated in both Fahrenheit and Celsius.

[Jdnewberry]

A few things that would be helpful in diagnosis:

-an infrared thermometer would be helpful in determining your coolant temperature at various points in the system
-check your plug color for evidence of correct mixture (light brown ash)
-bubbles in coolant or coolant loss indicating a gasket failure or crack

Plugs are the proper color, but may be accumulating slightly more ash than I would like to see. Not much, though. No visible bubbles in coolant, no oil in coolant, no coolant in oil, and no steam from tail pipe. I don't think it's the head gasket, but I'm not absolutely certain.

[Jdnewberry]

Keep in mind... running the engine at temperature without a thermostat will simply cause the coolant to flow through the bypass port rather than the radiator (the 'stat skirt blocks this port when functioning properly). This can cause the engine to run hot.

As Ignotus referenced, Teriann has a nice write up HERE

Thanks for the info. I wasn't aware of what the skirt actually did.

[Jdnewberry]

Does your gas gauge work?

I ask because, if it doesn't, it may be that your voltage stabilizer is not working and feeding your temp gauge and gas gauge the wrong voltage... and causing both to be inaccurate. It's harder to tell something's wrong with the temp gauge, but the gas gauge - it's more obvious if it's off. If the gas gauge is not accurate, try swapping out the stabilizer.

Also, consider the temp sender... Mine recently bonked. I noticed it when, within a minute of starting the engine, the gauge showed the engine as mid gauge on the temperature gauge... Does it warm up at the expected rate?

Bottom line - maybe the engine temp is just fine... the gauge just isn't accurate due to bad voltage stabilizer, bad sender or... even a bad gauge.

I have already been down that path. I purchased a new sender because mine didn't work when I purchased the truck. After installing, I noticed it running close to the red. The fuel was also inaccurate, so I drug out the old analog voltage meter. Stabilizer is fine. Looking deeper, I came across the radiator cap with the thermometer built in and verified the temp was high. I also pulled the fuel sender apart and found the wire windings are broken near the 'half tank' mark. That explains why it only holds 5 gallons when it hits empty!

Warm up time seems as expected. It takes 10-15 mins at idle or 2-3 mins of drive time. The gauge stays smack in the middle of 'N' indefinitely until I get up to highway speeds. The mechanic suspects the radiator, but I just can't see that too fast of a flow rate could cause this.