Hello everyone

I had a post on here befor about the tranny issues but I do not see it.

Well I am back here again with a new problem that is quite scary.
Out of the blue our temperature gauge start to move a lot between 160 to 250F. We replace the thermostat right away SAME problem notice we had quite a bit rust in the water, did a flush and put in rust removal and flush again then put 50/50 water and coolant in. Still same problem but less frequent. We try to check the sending unit but it a single wire so we cant check for ohms reading. We are not sure how to check the gauge and the sending unit. We are praying that it not the water pump (bad water flow) it was replace a few years ago and was doing fine till now. So we decided to remove the thermostat and ran it quite a few days and it DOSE NOT bounce around but it wont warm up to 160F on normal driving unless were on the freeway and if i am going fast 70-80mph on the i5 highway then temp will creep to 200F till the clutch on the fan engage and it rides at that temp for a long time till i slow down to like 60mph (traffic). Keep in mind it also will be random sometimes but not often 250F sometimes it stays betwen 160 to 200F. I put the stat back in to see if anything changes right off the bat it warm up to 200F and stay there if i am driving normaly when I have to give it a little gas like on the freeway i see it go to 250F I also decided it was time to turn on the heater causes i was cold.... MAJOR POOF of magic smoke FLOOD the cabin in moments and fog the windows and i coudlnt breath. Luckly I was off the freeway at the time.

So now the heater coil is busted and I am going to run a bypass to see if it was the heater coil causing the pressure and flow issues. I smell coolant befor when the heater was on but it was bareble. This heater coil leak started after I put the stat back in. IT was fine befor so my guese is the high pressure finaly push out w.e stop leak we had in there (the rust remover may had weaken it)


So what I need to know is what is the operating temp for this type of engine I live in the bay area so it almost ALWAYS cold.
How do I check the sending unit and the temp gauge.
How do I by pass the heater coil (think i can figure that one out but any tips and info will be great)

I have an H1 1995 6.5L non turbo Diesel
I should mention I tested the old and new thermostat in boiling water they both started to open at 190F...and fully open around 200F it weird causes my temp gauge always show 160F unless it have a load it gose higher especially on warmer days.
When i buy a new thermostat I was ask do I want 160F or 190F. Cuases I am use to seeing 160F I choose that and it work fine. The old one was rated for 160F (unless they are retard and gave me wrong one or there isnt a different) the old 160F actually open at 190F in boiling water. So I am really confuse

If you need info I forgot to put on here let me know hope we can solve this issues soon. Thank you for reading this.

 

Heater core bipass is easy. Check out flashoffroad.com for details and pictures on how to do it. Have you noticed much loss of coolant? Did you do a pressure test on the cooling system? It should hold 15 psi. The guages are notoriously inaccurate. Have you checked actual coolant temps?

 

Thanks for the reply. I don't have a way to check the pressure but it truly make sense why all the suddenly the temp change alot. I couldn't find the bypass on the website you gave me ,must be blind but I did find something on the internet. It was my original intent do complete bypass everything till we fix this core. Coolant loss was STUPID high, normally we loose a little bit here and there but this time when i was roaming with vaporize coolant in the cabin. I took the hose off the radiator and it did not drain I am stupid lucky i made it home without trashing my engine. She off the road now till I get this fix nothing worst having a blown engine causes of mess up cooling. I had it happen to me when a hose fell off my car on the freeway dint stand a chance causes I didn't pay attention. Now i always look at my interments panel.

Update: I ran the bypass end up cutting hoses it was dam near fuse but no biggy can get new hoses when we fix the heater.

Update2: I found this problem wile doing the bypass.
GOt a new problem it happen befor the wire from the bateries to the starter had melted....The first time this happen the orginal wireing melted and was shorting on the body causesing a dead battery in 3 days if it not in use. We fix it by trying to reroute the wire further away from the exhaust but it melted again but it not causing to much short but if it get wet it could causes a nice spark...got 2000amps behind that wire. Dose anyone have a soultion that had work well for them? such as what type of wire you use or heat shielding ? Can we rotate the solenoid on the starter so we can have the wire hook up further away from the exhaust? Thank you.