Vexing temp issue

[Petros]

Hi all,

I am helping someone fix an '86 T4wd with an apparent overheating issue.

The car had coolant in the oil, so I replace the head gasket, made sure the head was flat, did my gasket mod and put grooves in the combustion chamber, put in a new timing belt, water pump (old one was weeping), Thermostat, new coolant and oil.

Got it back together Started it and the gauge went to red zone very fast. Odd thing is the engine did not feel hot at all, I could put my hand on the upper rad hose (very warm, but not hot). Found out the fan switch was not working so unplugged it so it stayed on, still gauge went to red zone. Swapped out gauge sensor with good one, same issue.

Engine is not loosing coolant or showing any other signs of being hot, heater does not even put out warm air. But I am spooked at driving it with the temp in the red (I do not want to replace the head gasket again!).

Next thing I am going to try on Friday is swapping out the temp gauge, and try a different radiator in case the existing one is plugged. Also I thought I would check the temp gauge wire for grounding, if it is grounded it would go strait to red zone.

I do not see any thing else that is wrong with the cooling system, anyone have any other ideas I could test.

Thanks

[ARCHINSTL]

Before going to the trouble of switching stuff - could the thermostat be nonfunctioning? Perhaps test the water temp with a candy thermometer after carefully removing the cap - that would be a clue as to whether the temp is in the range (180 degrees or so?). Maybe some temp specs are in the FSM?
Tom M.

[animeracing]

My experience so far is the radiator fan motor goes out, which in turn causes everything listed in your post.

[takza]

Sounds like the sending unit or gauge is messed up. Any kind of thermometer to pick up the coolant temp in the engine itself would tell you what's to worry about? Oven thermo might work if you insulated the tip where it picks up the heat.

Fan isn't the issue? Thermostat might be?

[danzo]

Just point your infrared pyrometer (every engineer has one) to various points on the engine/cooling system to verify any hot spots. My guess is that you won't find any - it sounds like a bad temp gauge. Run a ground wire directly from the gauge to the negative battery post (British car trick) and see if the gauge reads correctly. If not, try another gauge.

It can't be the fan if it's running constantly, and is not likely to be the t-stat but possible. You mentioned luke warm heater output - maybe your killer headgasket mod works too good.

[Highlander]

I'd bet that the rad is plugged. My '85 had cooling issues that took me so far as to replace the head gasket- no change, but when I swapped another rad in, I realized that the one I took out weighed almost 2 lbs more than the replacement ! Loads of gunk in there from being filled with pond water or some such on the ranch in Wyoming (before I bought it). Check the rad temp by putting your hand on it while the engine runs, if its only mildly warm and the lower hose is hot, then you're not getting coolant through.

[Petros]

the rad test is a good one, but would not the upper hose be the hot one (engine outlet)? lower one is inlet hose. I am going to try it, and get a spare radiator from the wrecking yard (only about $30). I also have an aftermarket mechanical temp gauge I am going to plug into the the sender location to read temp independent of factory wiring or gauge.

I swapped the stock temp sender with one I knew was good, but the gauge still maxed out. I also grounded the gauge wire and the temp gage went to full hot, and to zero when it was unplugged. This is normal test for a gauge, but it is possible I guess that the gauge just reads too high if it is internally bad.

Fan works, the fan sender switch is bad, but gauge still shows overheat with fan running.

So either the gauge or gauge wiring is bad, the new thermostat is bad (and works exactly the same way the old one removed did), or the radiator is plugged (it otherwise looks normal on the outside). The old coolant BTW, did have a lot of rust in it, and that was after the owner claimed she just flushed it. So it could be a blocked up radiator, or not. It seems that just idling should not be enough demand to overheat the engine even with a blocked radiator, it would be rare it gets so blocked up it does not cool at all. My experience is it blocks up slowly, and first shows up as partially blocked on long hills, or other high demand conditions, but not just idling. Though I suppose anything is possible.

I kind of doubt it is the thermostat; so I will try gauge first, the replacement radiator second, and perhaps just remove the t-stat last to see if runs without overheating if first two tests fail.

[dlb]

in my typical fashion, i'm not great at diagnosing this stuff but i did have a similar experience when i put my new engine in several weeks ago. the temp gauge would get up to about 3/4 very quickly, regardless of what kind of driving or even idling the car was doing, and even when the engine didn't feel hot. i knew my old rad was fine since i never had problem with the old engine though, so i did one of those coolant flush things--drain the system, put the whole bottle in, fill the rest with water, drive it for 3-6 hrs, drain and flush it, fill it with water, let the engine idle with the heater on for 10 minutes, drain and flush it again, and finally fill it once more--and after that it's been dandy, even running cooler than the old engine. the stuff only costs $7 so if the coolant looked like hell you may as well do a good flush and clean it out regardless of temp issues.

this is probably old hat to most of you but when filling the coolant the final time i took my time. i found that the fluid level would come up the rad cap spout and then slowly go down again. i used to figure that was full, but by spending an extra 5 minutes and filling it until the level stayed right at the top of the rad cap i have found that i no longer have to top up the plastic reservoir on a regular basis like i used to. i guess i always used to run the car with too little coolant, causing the system to suck everything it could get from the reservoir in an attempt to fill itself up. live and learn.

[takza]

With an older car you'd probably want to avoid a cooling system flush chemical? Heater core problems?

You need to be sure there are no leaks or plugging of the tube from the rad to the reservoir and that you have a good cap.

[dlb]

why would a cooling system flush chemical cause heater core problems?

[danzo]

First step is to confirm that the damn thing is in fact overheating. Based on what has been said and the fact that the heater doesn't even blow hot, I vote the car is not running hot. Take a temp reading with a known accurate device before throwing parts at the car. Good luck and keep us posted.

[takza]

why would a cooling system flush chemical cause heater core problems?

Because the older a car is the more likely the cooling system is corroded to some degree...sometimes the lime deposits, rust, etc. are what's keeping them from leaking. If you do a search on this forum there was a former member who ran some cleaner and wished he hadn't.

Best bet is probably to just buy the Prestone flushing kit and reverse flush it...then be sure to use the 50/50 antifreeze mix and or the regular and distilled water. Just don't put full faucet water pressure on your cooling system...leave the cap off! Also if you use the Prestone kit...don't leave the plastic T in the heater line...they can crack.

[splatterdog]

Danzo's on to something here. More data needed.

Takza is correct to a degree on chemical flushes. It can open up holes. But if it's badly needed, the heater core and everything else that holds coolant can already be considered broken. If the rad,engine, or core can't transfer heat efficiently action needs to be taken. If it's real bad inside are you going to replace the rad, core, and all hoses and at the very least disassemble the engine for a professional cleaning? Might as well re-ring or full rebuild at this point....

I've done it to every one of my T4's. They all needed it badly. None have popped any leaks(knock on wood). Even the 84 that overheated horribly at least a couple times long ago and had a heater core fire due to chewed up napkin balls. The 86 parts car I got from mickeyD and drove for a year actually ran better by the end of a long scenic drive/flush. It had a thick orange layer on everything inside. Pretty sure it was from iron rich northern Mn. well water. Had the water outlet off the head and it was scrapeable. Looked new after.

Cooling systems are frequently neglected. Especially on cars that don't break very often. That could include just about everyone here that got their car when it was 15-20+ years young and maybe still circulating factory fluid.

I would get full strength coolant and mix your own. I don't know if I trust the premix jugs to have distilled water in the mix. Our friends to the north need it thicker than 50/50 too.

The flushing tees should be checked periodicaly for softness and brittleness. Putting it in the upper heater hose also makes the perfect bleeder for filling the system back up.

[Petros]

Got is all fixed friday afternoon. Here is how it went:

I decided to take the radiator out and inspect it carefully, it did not look bad, I filled it with straight vinegar and let is sit for an hour while I did some other repairs. I put in a new instrument cluster (I got an SR5 cluster at a wrecking yard cheap, and this car is a DX, so she got a new temp gauge, and a tach too!). Put in a different used thermal fan switch I got at the JY. Fixed a few other unrelated problems as well, installed a new mechanical temp gauge at the outlet where the computer input is located so I can compare both the new dash temp gauge with the mechanical gauge. We replaced the upper and lower hoses while we were at it (they looked the the factory hoses!). When I back flushed out the vinegar I got some large corn flake looking stuff, not a lot.

It all went beck together and it started and ran, watching both gauges it came up to about 210 and the fan came on, and held steady. The new dash temp gauge showed it holding at about half way up the gauge. No over heat, it looks like it was the gauge.

I set the timing at 10 deg BTDC, and in doing so discovered ther mechanical advance in the distributor is not working. Took the cap off and put pentrating oil in it, and tried to work it loose, but to no avail. I might bring a new distrubutor from the JY to swap out next time I work on it for her.

Anyway it is all working now so she can drive it. IT will need a clutch soon. That will be for next month.