94 6.5TD , Without thermostat temps won't go above 130 or 140. With 3 different new t-stats the temp goes up to normal 180-190
for a while then spikes to overheating then drops back to norm. If the head gasket was blown or cracked would it not do this with or without T-stat? I have tried to eliminate any air pockets best I could.

When " Spikes to overheating".....How much?......what's the number?

If the needle is pegged I would suspect the gauge.....Do you have a scan tool to tell you that your gauge is accurate?

Louis

Sounds like you may still have some air pockets in the block. Leo

First off, Welcome to the deisel place.

There is a wealth of information and experince here. Check out the FQA and other stickies at top of the 6.5 forum.
Add the details of your truck to your signature line, so every one knows want you are talking about.


For the 6.5, 180 / 190 is normal. You need this temperature to get the best power and mileage. put the Tsat back in.
brief ventures to 210, can be a concern but I've seen the fan clutch not fully lock in until 210.
Extended 210 or higher is an alarm. get out of the power or slow down some.

To reduce ventures higher than 190, look at fan and clutch upgrade. If pre 97, their are other cooling system upgrades, see Heath's or Kenedy's web site for information. (site supporting venders)
Also wash out the radiator with a pressure washer to make sure it is clean.



This winter, running on the highway with the snow plow blade too high and blocked some air flow into the radiator. I would see 210, then hear the fan clutch lock up. The temperature would drop right away. This was in 20F air.

This is at idle and revving the engine. Has not been road tested yet . I'm in NH so outside temp was only like in the 50's yesterday. I did read the faq's and did check the clutch fan.The upper hose gets real hard too! When I release the pressure using the little bleeder screw on the t-stat cover the temp goes back down. I dont understand why this is not happening with the t-sat removed. But when I leave it out, the motor does not get up to temp so it's blowing white smoke. I'll put my Genisys on later to get more accurate temps, but it is going up way over 210.


Thanks guys!

2 ?s
When you open the little bleeder screw to relieve the pressure are you getting a lot of air, or just water?
Which brand t-stats are you using?

When the temp surges up there is air at the bleeder.

As far as brand of t-stat its been 3 different ones and the latest is a Parts Plus.

It could be that once you get all of the air out of the system your problem will be solved. However you should read this http://www.dieselplace.com/forum/showthread.php?t=227928&highlight=thermostat concerning the thermostat.
Good luck!

Thanks for the info. Would you kindly point me in the right direction as to where to find the proper procedure for getting the air out if it's not too much trouble. TIA

Does the rad hose get hard soon after starting before it's up to temp? Leo

The hose gets hard after it gets up to temp. It's been running for a little over 5 minutes and is still soft.

Thank you for replying.

Hose getting hard at about 170

OK, things seemed normal for about a half hour . Would go to around 205 then t-Stat would open and would go down to like 185. Gauge was matching Scan tool reading. Then I noticed the heat was starting to get cold and needle rose to 260 but scanner was reading 158. A minute or 2 later it started spewing out the overflow and scanner reading went up to match the gauge then .After that it went down to normal temp.:eek: I'm, so confused.

Forgot to add that now after it spewed the low coolant lite obviously came on.

Check for compresion leaks.

This thread shows a procedure to test and narrow down a leak.

http://www.dieselplace.com/forum/showthread.php?t=198698

Its quick and easy, doesn't require tearing down the motor.

You seem to describe a compression leak. Have you bleed the system more than twice?
If air keeps building while it runs, then I would say you have a leak. With the Tstat closed, the only place for air to go is build up behind the tstat or get forced through the heater core. When the air buble builds, coolant backs up into the reservoir until it get pushed out.


If your not getting new air into the system, over heating might mean a water pump issue.

Hi thanks for the reply, I've been searching here for the best way to bleed the coolant system. Could you please point me in the right direction. TIA

Please fill out your signature!
I did a quick search for "coolant system" and came up with a bunch of hits. Try these:
http://www.dieselplace.com/forum/showthread.php?t=165581
http://www.dieselplace.com/forum/showthread.php?t=205625&highlight=coolant+system
http://www.dieselplace.com/forum/showthread.php?t=165650&highlight=coolant+system

READ THE STICKIES TOO

Thanks I finally located a couple good threads a few minutes ago about it. I will fill out my sig ASAP! Thanks man.

When " Spikes to overheating".....How much?......what's the number?

If the needle is pegged I would suspect the gauge.....Do you have a scan tool to tell you that your gauge is accurate?

Louis

????

Sounds like an air pocket in the system or possibly the dreaded head gasket. If it's spewing out the overflow it's not the gauge. The gauge may be reading odd 'cause of air in the system as air dosen't conduct like the cooling fluid does. I'd bleed and bleed until your sure all the air is out, then see if the air comes back. If so, there is a compression leak somewhere. May not pressurize until it gets hot and then the crack (or gasket) expands and then compression gets by.
Don

Thanks for all your posts. I'm fairly convinced that it is a crack like daustin says. The head gaskets were replaced and no cracks visible to the naked eye were seen.

That might be one of those cracks that don't open up until the head gets up to operating temp. Had that happen to a camaro i had many years ago. A quick easy way to find a crack once the head is off is wipe it with Laquer thinner, the crack will "spider" the thinner expecially if the part is engine internal and oil soaked.
Don

Check between the a/c condensor and the rad.The fins of the rad it self could be plugged.Have seen many clogged up around the center of the rad where you can't see with road dust ect.

Just to update! From all the great info all you fine ppl have provided at this site, I decided to get an OEM t-stat and an OEM rad cap. Between that and a last ditch effort at bleeding the system , I think the prob is solved and would like to thank all that helped me out.:)

It took about five minutes after I installed the $28 t-stat to realize something was different. It has been running for a very long time and there is no spewing coolant or temp spikes. I can't road test it because the boss hasn't registered it yet but I'm hoping for the best. Once again , Thank You All